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JNCIS-SEC Study Guide—Part 1. Copyright © 2010, Juniper Networks, Inc. All rights reserved. Printed in USA.
The information in this document is current as of the date listed above.
The information in this document has been carefully verified and is believed to be accurate for software Release 10.1R1.8. Juniper Networks assumes no responsibilities for any inaccuracies that may appear in this document. In no event will Juniper Networks be liable for direct, indirect, special, exemplary, incidental or consequential damages resulting from any defect or omission in this document, even if advised of the possibility of such damages.
Contents
Chapter 1:
Introduction to Junos Security Platforms . . . .1-1
Chapter 2:
Zones . . . .2-1
Chapter 3:
Security Policies . . . .3-1
Chapter 4:
Firewall User Authentication . . . .4-1
Chapter 5:
SCREEN Options. . . .5-1
Chapter 6:
Network Address Translation . . . .6-1
Chapter 7:
IPsec VPNs . . . .7-1
Chapter 8:
Introduction to Intrusion Detection and Prevention . . . .8-1
Chapter 9:
High Availability Clustering . . . .9-1
Welcome to the JNCIS-SEC Study Guide—Part 1. The purpose of this guide is to help you prepare for your JN0-332 exam and achieve your JNCIS-SEC credential. The contents of this document are based on the Junos for Security Platforms course. This study guide covers the configuration, operation, and implementation of SRX Series Services Gateways in a typical network environment. Key topics within this study guide include security technologies such as security zones, security policies, intrusion detection and prevention (IDP), Network Address Translation (NAT), and high availability clusters, as well as details pertaining to basic implementation, configuration, and management.
Agenda
Chapter 1: Introduction to Junos Security Platforms Chapter 2: Zones
Chapter 3: Security Policies
Chapter 4: Firewall User Authentication Chapter 5: SCREEN Options
Chapter 6: Network Address Translation Chapter 7: IPsec VPNs
Chapter 8: Introduction to Intrusion Detection and Prevention Chapter 9: High Availability Clustering
CLI and GUI Text
Frequently throughout this study guide, we refer to text that appears in a command-line interface (CLI) or a graphical user interface (GUI). To make the language of these documents easier to read, we distinguish GUI and CLI text from chapter text according to the following table.
Input Text Versus Output Text
You will also frequently see cases where you must enter input text yourself. Often this will be shown in the context of where you must enter it. We use bold style to distinguish text that is input versus text that is simply displayed.
Style Description Usage Example Franklin
Gothic
Normal text. Most of what you read in the Student Guide. Courier New Console text: • Screen captures • Noncommand-related syntax GUI text elements:
• Menu names • Text field entry
commit complete
Exiting configuration mode
Select File > Open, and then click Configuration.conf in the Filename text box.
Style Description Usage Example Normal CLI
Normal GUI
No distinguishing variant. Physical interface:fxp0, Enabled
View configuration history by clicking Configuration > History.
CLI Input GUI Input
Text that you must enter. lab@San_Jose> show route Select File > Save, and enter
config.ini in the Filename
Finally, this study guide distinguishes between regular text and syntax variables, and it also distinguishes between syntax variables where the value is already assigned (defined variables) and syntax variables where you must assign the value (undefined variables). Note that these styles can be combined with the input style as well.
Style Description Usage Example
CLI Variable GUI variable
Text where variable value is already
assigned. policy my-peers
Click on my-peers in the dialog.
CLI Undefined GUI Undefined
Text where the variable’s value is the user’s discretion and text where the variable’s value might differ from the value the user must input.
Type set policy
policy-name.
ping 10.0.x.y
Select File > Save, and enter
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About This Publication
The JNCIS-SEC Study Guide—Part 1 was developed and tested using software Release 10.1R1.8. Previous and later versions of software might behave differently so you should always consult the documentation and release notes for the version of code you are running before reporting errors.
This document is written and maintained by the Juniper Networks Education Services development team. Please send questions and suggestions for improvement to [email protected].
Technical Publications
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• Go to http://www.juniper.net/techpubs/.
• Locate the specific software or hardware release and title you need, and choose the format in which you want to view or print the document.
Documentation sets and CDs are available through your local Juniper Networks sales office or account representative.
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For technical support, contact Juniper Networks at http://www.juniper.net/customers/ support/, or at 1-888-314-JTAC (within the United States) or 408-745-2121 (from outside the United States).
Chapter 1: Introduction to Junos Security Platforms
This Chapter Discusses:
• Traditional routing and security implementations; • Current trends in internetworking;
• SRX Series Services Gateways;
• The Junos operating system for the SRX Series; and
• Physical and logical packet flow through SRX Series devices.
Built to Forward Packets
The primary responsibility of a router is to forward packets using Layer 3 IP addresses found in an IP packet header. To forward packets, the router must have a path determination mechanism. This mechanism could be statically assigned routes, routing protocols, or policy-based routing.
Packet Processing Is Stateless
Traditionally, routers process packets in a stateless fashion. Routers do not keep track of bidirectional sessions; they forward each packet individually based on the packet header.
Separate Broadcast Domains and Provide WAN Connectivity
Routers were originally used to separate broadcast domains. With the introduction of advanced switching technologies and the birth of virtual LAN (VLAN) standards, broadcast domains can also be separated using switches. That capability, however, does not address inter-VLAN connectivity, which still necessitates the use of routers for forwarding traffic between VLANs. Furthermore, routers provide WAN connectivity at the network edge.
Layer 3 Packet Forwarding
The graphic illustrates the transmission of packets from host 10.1.1.10 to host 10.3.3.10. Routers perform Layer 3 packet forwarding using routing table entries. Routers build routing tables based on the results of dynamic routing protocols (for example, RIP, OSPF, IS-IS, and BGP), statically entered routes, or both of these methods. Note that routers forward packets based on the longest prefix match. For example, on the graphic, Router A selects interface ge-0/0/2 to send traffic to destination 10.3.3.10 because 10.3.3.10/32 is a longer prefix match than 10.3.3.0/24. If entry 10.3.3.10/32 does not exist in the routing table, the router selects interface ge-0/0/0 as the next hop for the same packet flow.
Promiscuous Behavior of a Traditional Router
A traditional router is a promiscuous device that performs stateless packet processing. It is promiscuous because once it is configured, it immediately forwards all traffic by default (provided, of course, that some combination of static and dynamic routing is configured). Typically, a router operates only at Layer 3 and does not recognize any security threats in higher-layer protocols. Furthermore, a traditional router operates per packet, which adds to its fundamentally insecure nature, because it cannot detect malformed sessions. The network and the router itself are immediately vulnerable to all security threats.
Typical Treatment of Security
Typical Router Positioning
Enterprise customer premise applications are served by the J Series family of service routers and, in the case of larger enterprises, M Series routers. Enterprise data center applications can also be served by M Series routers. Internet service provider (ISP) networks can be served by M Series, MX Series, or T Series routers. J Series, M Series, MX Series and T Series routers support the rich routing and class-of-service (CoS) features needed by networks, and maintain value, stability, and predictably high performance.
Adding Security to the Network
Standalone routers do not provide adequate security to enterprise networks and data centers. As networks expand, network applications continue to diversify and expand, and as new methods of remote communications such as telecommuting increase, the need for added security becomes apparent. Typically, a standalone firewall is added to the network, increasing costs and maintenance.
Requirements for Firewall Devices
A firewall device must be capable of the following:
• Stateful packet processing based on contents of IP and higher-level packet information, which includes TCP/UDP and the Application Layer;
• Network Address Translation (NAT) and Port Address Translation (PAT), achieving private-to-public translations and vice versa; and
• Establishing virtual private networks (VPNs) compounded with authentication and encryption.
Additional Services
The growth in network security has resulted in additional services provided by standalone firewalls such as Secure Sockets Layer (SSL) network access, intrusion detection and prevention (IDP), application-level gateway (ALG) processing, and more.
Firewall: Stateful Packet Processing
Because the main job of a firewall is to protect networks and devices, fundamental firewall intelligence consists of the ability to make packet processing decisions based on IP packet header information, including its upper layers. Stateful packet processing involves the creation of a unidirectional flow, which consists of six elements of information—source IP address, destination IP address, source port number, destination port number, protocol number, and a session token. The session token is derived from a combination of a routing instance and a zone. The outgoing flow initiates a session table entry and the expected return flow for that packet. Both outgoing and incoming flows comprise the session and are entered into the session table. The session table enables bidirectional communication without any additional configurational steps for return traffic.
Firewall: NAT and PAT
When a security device resides at the edge of a network, it must be able to replace private, nonroutable addresses with public addresses before traffic is sent to the public network. Translation can consist of replacing the IP address, port numbers, or both, depending on the configuration. Note that NAT can be used on both source and destination addresses, and PAT can be used on both source and destination ports.
Firewall: Virtual Private Networks
You can use a firewall to build VPNs using the public network as an access medium between two private sites. As such, the firewall must be able to perform the following:
• Encapsulate the original traffic in a packet that can be transported over the public network;
• Encrypt the original packet so that it cannot be easily decoded if it is intercepted on the public network; and
• Authenticate the originating device as a member of the VPN—not a random device operating on the public network.
Firewall Positioning
The enterprise firewall device at the central site provides VPN termination and firewall protection between internal zones as well as from the Internet, and it might also provide other security services such as IDP, Web filtering, and antispam services.
Current Trends
As boundaries of networks are becoming less clear, so are the requirements of network edge devices. More and more enterprises are interconnecting themselves through an ISP’s virtual cloud by using IP. The Internet has created possibilities and opportunities for businesses and markets, and it has erased the concept of distance. With the Internet, however, came network vulnerabilities. Traditionally, routers have been positioned on the edge of an enterprise network and provided very basic network security such as stateless firewall filters. Network administrators became used to relying on separate firewall devices positioned within enterprise DMZs. The consolidation of these functions at the network edge improves costs, reduces management overhead, and increases operational simplicity.
A New Perspective
The graphic illustrates how a device with strong routing and firewall features can be positioned at network boundaries. Remote offices can deploy SRX Series branch platforms running the Junos OS to provide both routing and security features.
The SRX Series Services Gateway at the enterprise headquarters in this example also provides routing and security in a high-density, modular chassis. The Dynamic Services Architecture allows SRX Series Services Gateways to leverage new services with appropriate processing capabilities without sacrificing overall system performance. SRX Series Services Gateways are next-generation systems designed to meet the network and security requirements for the enterprise and service provider infrastructure, and facilitate data center consolidation, rapid managed services deployments, and security services aggregation.
SRX Series High-End Systems
The Juniper Networks SRX Series Services Gateways for the high end are next-generation services gateways based on a revolutionary architecture that provides market-leading scalability and service integration. These devices are ideally suited for large enterprise and service provider networks:
• Securing large enterprise data centers;
• Securing service provider and collocated data centers;
• Aggregating departmental or segmented security solutions; and • Securing managed services and core service provider infrastructure.
Based on the Dynamic Services Architecture, the SRX Series provides unrivaled scalability. Each services gateway can support almost linear scalability with each additional Services Processing Card (SPC), enabling a fully equipped SRX5800 to support more than 120 Gbps of firewall throughput. The SPCs are designed to support a wide range of services enabling future support of new capabilities without the need for service-specific hardware. Using SPCs on all services ensures that no resources are idle, based on specific services being used, maximizing the utilization of equipped hardware.
The scalability and flexibility of the SRX5000 and SRX3000 lines of services gateways are supported by equally robust interfaces. The SRX Series high-end line employs a modular approach to interfaces where the gateway can be equipped with a flexible number of input/output cards (IOCs).
With the IOCs sharing the same interface slot as the SPCs, you can configure the gateway to support the ideal balance of processing, input, and output. Hence, you can tailor each deployment of the SRX Series to specific network requirements. With this flexibility, you can configure the SRX5800 to support more than 400 gigabit ports, with choices of Gigabit Ethernet or 10-Gigabit Ethernet.
The feature integration on the SRX Series is enabled by the Junos OS. By combining the routing heritage of the Junos OS and the security heritage of ScreenOS, the SRX Series is equipped with a robust list of features that include firewall, intrusion detection and prevention (IDP), denial of service (DoS), Network Address Translation (NAT), and quality of service (QoS).
SRX Series High-End System Components
The SRX Series line of high end systems includes the following integral components:
• Input/output card (IOC): To provide the most flexible solution, the SRX Series employs the same
modular architecture for SPCs and IOCs. With the flexibility to install an IOC or an SPC on a given slot, the SRX Series can be equipped to support an ideal balance between interfaces and processing capabilities.
• Network Processing Card (NPC): To ensure maximum processing performance and flexibility, the
SRX3000 line utilizes NPCs to distribute inbound and outbound traffic to the appropriate SPCs and IOCs, to apply QoS, and to enforce DoS and distributed DoS (DDoS) protections. In the SRX5000 line, the NPC is integrated into the IOC. Note that a minimum of one NPC must be installed in platforms in the SRX3000 line to ensure proper functionality.
• Services Processing Card (SPC): SPCs are designed to process all available services on the gateway.
Without the need for dedicated hardware for specific services or capabilities, no instances exist in which a piece of hardware is taxed to the limit while other hardware is sitting idle. All the processing capabilities of the SPCs are designed to process all configured services on the gateway. Note that a minimum of one SPC must be installed in an SRX Series high-end system to ensure proper functionality. • Switch Control Board (SCB): The SCB monitors and controls system functions and provides the
interconnections to all the IOCs within a chassis through the switch fabrics integrated into the SCB. At least one SCB is required for the system to function. Two or three SCBs increase capacity or provide redundancy, depending on the specific platform.
• Routing Engine (RE): The RE is an Intel-based PC platform that runs the Junos OS. Software processes
that run on the RE maintain the routing tables, manage the routing protocols, control some chassis components, and provide the interface for system management and user access to the device.
For more information on specific SRX Series high-end system models and hardware, visit the Juniper Networks Web site for technical publications at http://www.juniper.net/techpubs.
Physical packet flow through a high-end security platform proceeds through the following sequence of steps: 1. A packet enters the security platform through the IOC.
(Step 1.5: Oversubscription control applies at the IOC.)
2. The packet traverses the switch fabric from the IOC to the NPC. (In the SRX5000 line of products, the NPC integrates with the IOC.) The NPC performs a flow lookup. If the packet belongs to an existing flow, the NPC forwards the packet to the SPC associated with the packet’s session. If the flow does not currently exist, the NPC installs a new session for the flow and assigns the flow to an SPC for processing. The NPC also performs CoS, policing, and shaping.
3. The packet traverses the switch fabric to its associated SPC, where security processing and forwarding or routing occurs.
4. The packet traverses the switch fabric back to an NPC where additional packet processing such as shaping and CoS occurs.
5. The packet traverses the switch fabric to the IOC associated with the egress interface and travels to the attached physical medium.
SRX Series Branch Devices
Juniper Networks SRX Series Services Gateways for the branch provide essential capabilities that connect, secure, and manage workforce locations sized from handfuls to hundreds of users. By consolidating fast, highly available switching, routing, security, and applications capabilities in a single device, enterprises can economically deliver new services, safe connectivity, and a satisfying end user experience.
SRX Series for the branch operates with the Junos OS, the proven operating system used by core Internet routers in all of the top 100 service providers around the world. The rigorously tested carrier-class routing features of IP version 4 (IPv4)/IP version 6 (IPv6), OSPF, BGP, and multicast have been proven in over 10 years of worldwide deployments. SRX Series Services Gateways for the branch provide perimeter security, content security, access control, and network-wide threat visibility and control. Best-in-class firewall and VPN technologies secure the perimeter with minimal configuration and consistent performance. By using zones and policies, even new network administrators can configure and deploy an SRX Series branch device quickly and securely. Policy-based VPNs support more complex security architectures that require dynamic addressing and split tunneling. For content security, SRX Series for the branch offers a complete suite of Unified Threat Management (UTM) services consisting of intrusion
Select models feature Content Security Accelerator for high-performance IPS and antivirus performance. Junos security platforms for the branch integrate with other Juniper Networks security products to deliver enterprise-wide unified access control and adaptive threat management. These capabilities give security professionals powerful tools in the fight against cybercrime and data loss.
Branch Platform System Components
The SRX Series line of Junos security platforms include the following integral components:
• Multi-core processing unit: The processing unit uses multiple hardware threads to provide data plane
services including security services and control plane services to the branch device. The SRX branch line of platforms utilizes a system-on-a-chip (SOC) multi-core processor that provides the control and data plane functions as well as additional services such as Ethernet controller technology and a cryptographic engine.
• Physical Interface Modules (PIMs): The SRX Series line of branch and enterprise devices provide various
media interfaces known at PIMs. The media support includes 10/100 Ethernet, 10/100/1000 Ethernet, Gigabit Ethernet, T1/E1, T3/E3, ISDN, serial, ADSL and G.SHDSL interfaces, depending on the model. Some SRX Series branch models also contain an ExpressCard slot for utilization with a 3G wireless card to serve as a backup for primary interfaces. Select models contain Power over Ethernet (PoE) enabled ports.
• Services and Routing Engine (SRE): The SRE, a field replacable unit in the SRX650, houses the
processing unit and provides processing power for security services; routing protocol processes; and other software processes that control the services gateway interfaces, some of the chassis
components, system management, and user access to the device.
For more information on specific Junos security platform branch models and hardware, visit the Juniper Networks Web site for technical publications at
http://www.juniper.net/techpubs.
Physical Packet Flow for Branch Security Platforms
In SRX Series branch gateways, control and data plane separation is maintained using multiple threads on multiple cores within the processor. One hardware core is used for control plane functions. Packets ingress the device through built-in ports or PIM ports and pass to an Ethernet switch, which acts as the switch fabric for the device. In SRX Series branch devices, local switching occurs at the switch so that the CPU or the NPU is not taxed with switched traffic. As a result, security services such as security policy and IDP are not available with locally switched traffic. The switch performs CoS classification and traffic policing. It then passes non-locally switched packets to the processor where security services, routing lookup, and forwarding lookup is performed. SRX branch devices then send egress
Depending on the device type, the CPU might perform hardware acceleration and cryptographic acceleration. Some branch devices are equipped with a separate regular expression (REGEX) content processor to provide
hardware-based pattern matching for IDP and antivirus acceleration.
Junos Security Platforms Versus a Traditional Router
The traditional router and a Junos security platform have completely different starting points with respect to security and traffic flow.
The traditional router begins by forwarding all traffic. Thus, the network is vulnerable to all threats. You add security policies to reduce vulnerability until you reach the ideal configuration. Because the traditional router begins as completely promiscuous and it requires that you add security policies, a greater chance exists that the network will remain vulnerable to some threats.
An SRX Series Services Gateway running the Junos OS begins by forwarding no traffic. The network is secure but not functional. You add rules to allow traffic until you reach the ideal configuration. Because a Junos security platform begins by forwarding no traffic and because you must add rules, a greater likelihood exists that the network will restrict undesirable traffic.
The Junos OS for Security Platforms Merges Routing and Security
The new features of the Junos OS for security platforms bring new core security capabilities to the Junos OS. Because the forwarding algorithm is session-based, security features are tightly integrated into the forwarding plane, improving security performance. Session-based forwarding and stateful firewall features derive from Juniper Networks ScreenOS software.
Junos security platforms incorporate ALG functionality, IPsec VPNs, and screen protection in a flowd module within the Junos OS. Juniper Networks world-class IDP technology is also fully integrated into the Junos OS for security platforms. We discuss these features later in this material.
Junos Elements
SRX Series Services Gateways use the Junos OS as their base operating system. As such, these devices deploy all the industry-proven processes of the Junos OS, such as the routing process, management process, device control process, and others. Another building element of the Junos OS for security platforms is session-based forwarding, thereby resulting in a strong suite of security features.
Packet-Based Junos Forwarding
The Junos OS basic control plane, routing protocol process implementation, per-packet stateless filters, policers, and CoS functions are all packet based. Furthermore, other nonsecurity-related features, such as all interface
encapsulations and de-encapsulations, use the industry-proven Junos OS. You can configure SRX Series Services Gateways using either the CLI or J-Web—the Junos OS-based graphical user interface (GUI).
Session-Based Forwarding
The Junos OS for security platforms leverages ScreenOS software’s security features as well as its flow-based nature. The first packet entering the device follows a series of path and policy determination schemes. The Junos OS caches the session information, the creation of which is triggered by the first packet of the flow. The cached session is used by subsequent packets of that same flow and the reverse flow of that session. Using the flow module, which is integrated into the forwarding path, the hardware performs data-plane packet forwarding. Because the Junos OS for security platforms is security-based, all IPv4 packets entering the services gateway on an interface associate with an incoming zone. Likewise, all IPv4 packets exiting the device on an interface associate with an outgoing zone. The Junos OS for security platforms adds a bundle of high-security features to the regular features of a router, including stateful firewall, VPNs, NAT, ALGs, and IDP.
Control Plane
The control plane on a Junos security platform is implemented using the Routing Engine. The control plane consists of the Junos kernel, various processes, chassis management, user interface, routing protocols and some security features. Many of the security features resemble ScreenOS features, including the network security process, the VPN process, the authentication process, and Dynamic Host Configuration Protocol (DHCP). For its control plane, the Junos OS for security platforms deploys these features along with well-known, traditional Junos features.
Data Plane
The data plane on Junos security platforms, implemented on IOCs, NPCs, and SPCs for high-end devices and on CPU cores and PIMs for branch devices, consists of Junos OS packet-handling modules compounded with a flow engine and session management like that of the ScreenOS software. Intelligent packet processing ensures that one single thread exists for packet flow processing associated with a single flow. Real-time processes enable the Junos OS to perform session-based packet forwarding.
Logical Packet Flow Details
Security platforms running the Junos OS handle an incoming packet as follows:
1. The software applies stateless policing filters and CoS classification to the packet at the ingress. 2. If the packet does not drop, the software performs a session lookup to determine whether the packet
belongs to an existing session. The Junos OS matches on six elements of traffic information for this determination—source IP address, destination IP address, source port number, destination port number, protocol number, and a session token.
3. If the packet does not match an existing session, the software creates a new session for it. This process is referred to as the first-packet path. If the packet matches a session, the software performs fast-path processing.
The first packet of a flow is subject to first-packet-path processing. The software takes the following steps during first-packet-path processing:
1. Based on the protocol used and its session layer (TCP or UDP), the software starts a session timer. For TCP sessions, the default timeout is 30 minutes. For UDP sessions, the default timeout is 1 minute. These values are the defaults, and you can change them.
2. The software applies firewall SCREEN options.
3. If destination NAT is used, the software performs address allocation.
4. Next, the software performs the route lookup. If a route exists for the destination prefix, the software takes the next step. Otherwise, it drops the packet.
5. The software determines the packet’s incoming zone by the interface through which it arrives. The software also determines the packet’s outgoing zone by the forwarding lookup.
6. Based on incoming and outgoing zones, the corresponding security policy is determined and a security policy lookup takes place. The software checks the packet against defined policies to determine how to treat the packet.
7. If source NAT is used, the software performs address allocation. 8. The software sets up the ALG service vector.
9. The software creates and installs the session. Furthermore, the software caches the decisions made for the first packet into a flow table, which subsequent packets of that flow use.
10. The packet now enters the fast-path processing.
Subsequent packets of a flow are all subject to fast-path processing. The software takes the following steps during fast-path processing:
1. The software applies firewall SCREEN options. 2. The software performs TCP checks.
3. The software applies NAT. 4. The software applies an ALG.
5. The software applies packet forwarding features, which include the following: a. Stateless packet filters;
b. Traffic shaping by packet; and
c. Packet encapsulation and transmission.
Session Maintenance
When a packet enters the system and does not match any existing sessions, the Junos OS creates a new session based on routing and security policy information. Once this new session is created, the software puts it into a session hash table for further packet matching and processing. Depending on the protocol and service (TCP or UDP), the session is programmed with a default timeout. The default TCP timeout is 30 minutes and the UDP default timeout is 1 minute.
Session Cleanup
If no traffic matches the session during the service timeout, the Junos OS ages out the session and frees it to a common resource pool for a later reuse.
Session Run-Time Changes Propagation
The flow module is responsible for propagating any run-time changes that happen during the lifetime of the session. This propagation allows new packets that match the session to forward using up-to-date information. Routing run-time changes always propagate into the session. Security policy run-time changes might propagate into the session in progress, based on the corresponding security policy configuration.
Packet Flow Example: Part 1
We now apply the described decision process to a specific example. As the graphic shows, Host-B at 10.1.20.5 wants to initiate an HTTP session with the Web server at 200.5.5.5. The traffic passes through an SRX Series Services Gateway and is therefore subject to the decision process.
Packet Flow Example: Part 2
The graphic shows the packet as received by the SRX Series Services Gateway on interface ge-0/0/1. Following the flowchart, you can track the progress of the packet through the services gateway:
1. Based on a lookup in the session table, the Junos OS determines that this session is not an existing session.
Packet Flow Example: Part 3
The following is a continuation of the list from the previous page:
4. The packet is from host 10.1.20.5 and is an HTTP packet. This packet matches the policy statement on the graphic. The action for this particular type of traffic is to permit it.
5. The SRX Series Services Gateway adds the flow information to the session table. At the same time a return flow is automatically created and also adds to the session table.
6. The SRX Series Services Gateway then forwards the packet out
interface ge-1/0/0 (as determined by the destination lookup). The Junos OS allows traffic in both directions for this particular session to pass without any subsequent policy evaluation.
Answers
1.
Traditionally, routers process packets on a per-packet basis. 2.
Traditionally, firewalls process packets based on stateful flows. 3.
Junos OS for security platforms uses session-based packet forwarding and by default does not allow traffic to pass, whereas the traditional Junos OS uses packet-based forwarding and by default allows all traffic to pass.
4.
Chapter 2: Zones
This Chapter Discusses:
• Zones and their purpose; • Types of zones;
• Application of zones; • Configuring zones; and • Monitoring zones.
Zone Definition
A zone is a collection of one or more network segments sharing identical security requirements. To group network segments within a zone, you must assign logical interfaces from the device to a zone.
Traffic Regulation Through a Junos Security Platform
Zones enable network security segregation. Security policies are applied between zones to regulate traffic through the security platform running the Junos operating system. By default, all network interfaces belong to the
system-defined Null Zone. All traffic to or from the Null Zone is dropped. Special interfaces including the fxp0 management ethernet interface present in some SRX Series platforms, chassis cluster fabric interfaces, and internal system em0 interfaces cannot be assigned to a zone.
Review: Packet Flow
Recall the packet flow through a Junos security platform. Specifically, once the packet enters a flow module, the device examines it to determine whether it belongs to an already established session. Recall that the Junos OS matches on six elements of traffic information to identify a session—source IP address, destination IP address, source port number, destination port number, protocol number, and a session token.
This material focuses on defining, configuring, and monitoring zones.
Zones and Interfaces
You can assign one or more logical interfaces to a zone. You can also assign one or more logical interfaces to a routing instance. You cannot assign a logical interface to multiple zones or multiple routing instances. You must also ensure that all of a zone’s logical interfaces are in a single routing instance. Violating any of these restrictions results in a configuration error as shown in the following examples:
[edit]
user@host# commit check
[edit security zones security-zone trust] 'interfaces ge-0/0/2.0'
Interface ge-0/0/2.0 already assigned to another zone error: configuration check-out failed
[edit]
lab@host# commit check
[edit routing-instances A interface] 'ge-0/0/0.0'
RT Instance: Interface ge-0/0/0.0 already configured under instance B [edit routing-instances B]
'interface'
Interface ge-0/0/0.0 is in more than one routing instance (latest A) error: dcd_config_read fails to set parsing options
error: configuration check-out failed [edit]
'interfaces ge-0/0/2.0'
Interface ge-0/0/2.0 must be in the same routing instance as other interfaces in the zone
error: configuration check-out failed
One exception to the rule exists when all interfaces are assigned to one zone using the interface all configuration option. In this case, interfaces can belong to multiple routing instances.
Interfaces, Zones, and Routing Instances
The graphic summarizes logical relationships between interfaces, zones, and routing instances.
Logical interfaces are connections to specific subnets. Zones are logical groupings of logical interfaces with a common security requirement, and a logical interface can belong to only one zone. Zone configuration can be as simple as a two-zone setup, where all interfaces connected to internal networks are in one zone, and all interfaces connected to the external world are in a different zone. A more complicated configuration might divide interfaces based on internal department or function in addition to external and demilitarized zone (DMZ) connections. A physical device can be broken up into multiple routing instances. A routing instance is a logical routing construct within a platform running the Junos OS. Each routing instance maintains its own routing table and forwarding table. A routing instance can contain one or more zones, which cannot be shared with other routing instances.
The zones within the Junos OS can be subdivided into two categories—user-defined and system-defined. You can configure user-defined zones, but you cannot configure system-defined zones. You can subdivide the user-defined category into security and functional zones. We cover user-defined and system-defined zones in detail on the next few pages.
Security Zones
Security zones are a collection of one or more network segments requiring regulation of inbound and outbound traffic through the use of policies. Security zones apply to transit traffic as well as traffic destined to any interfaces belonging to the security zone. You need one or more security policies to regulate intrazone and interzone traffic. Note that the Junos OS does not have any default security zones, and you cannot share a security zone between routing instances.
Functional Zones
Functional zones are special-purpose zones that cannot be specified in security policies. Note that transit traffic does not use functional zones. While the fxp0 management ethernet interface is out-of-band by default, the Management Zone allows you to assign other network interfaces the same behavior of isolating management traffic from transit traffic.
Null Zone
Currently there is only one system-defined zone, the Null Zone. By default, an interface belongs to the Null Zone. You cannot configure the Null Zone. When you delete an interface from a zone, the software assigns it back to the Null Zone. The Junos OS rejects all traffic to and from interfaces belonging to the Null Zone.
Branch Platforms
Junos security platforms for the branch ship from the factory with a template configuration that includes security zones. SRX Series high-end platforms do not contain zones in the factory-default template configuration and, therefore, you must configure required zones manually.
Factory-Default Configuration
In branch devices’ factory-default configuration, two security zones are defined—trust and untrust. In the template configuration, vlan.0 belongs to the trust zone. In addition, the factory-default configuration file has a security policy permitting all transit traffic within the trust zone and from the trust zone to the untrust zone. The security policy prohibits any traffic from the untrust zone to the trust zone. We discuss security policy in further detail in subsequent material. The zone names trust and untrust have no system-defined meaning. Like any zones defined in the configuration, you can modify or delete them. You can revert a Junos platform to its
factory-default configuration by entering the load factory-default command from the top of the configuration hierarchy.
Zone Configuration Procedure
Zone configuration involves the following steps: • Define a security or a functional zone; • Add logical interfaces to the zone; and
• Optionally, identify some combination of system services and protocols allowed into the device through the interfaces belonging to the zone. If you omit this step, all traffic entering through the zone’s interfaces destined for the device is blocked.
Configuration Mode
To define a zone you must enter configuration mode, as illustrated on the graphic.
Defining a Zone Type
Once you enter the configuration mode, you can define a zone type. Recall that you can configure only two types of zones—functional, which is used for device management only (no transit traffic is permitted), and security. You define zones under the security configuration stanza. Note that user-defined zone names are case sensitive and can contain any standard characters, like any other variable name in the Junos OS.
Functional Zone Specifics
The following are two important configuration characteristics of the functional zone: 1. You can define only one type of functional zone—management; and 2. The functional zone does not have a user-defined name.
Adding Logical Interfaces to the Zone
Now you are ready to add logical interfaces to the zone. The graphic illustrates two variations. The first example illustrates adding interface ge-0/0/1.0 to the security zone, called HR, and the second example illustrates adding interface ge-0/0/1.100 to the functional management zone. If you omit the specification of the logical unit of the interface, the Junos OS assumes unit 0. Also, you can assign all interfaces to a zone by using the keyword all. Should you choose to assign all interfaces to a zone, you will not be able to assign any interfaces to a different zone.
Specifying Types of Traffic Permitted into the Device: Part 1
Specifying Types of Traffic Permitted into the Device: Part 2
When specifying types of traffic permitted into a Junos security platform, you use some combination of
system-services and protocols configuration options. The Junos OS provides you with the ability to refer to
all system services and protocols and respective ports with the help of the all keyword. To open all ports for all services, use the any-service keyword. In addition, you can isolate any exceptions to the referred list of protocols or system services with the help of the except keyword. The examples on the following pages illustrate the use of this keyword.
You can specify any of the following system services: [edit security zones]
user@host# set security-zone HR host-inbound-traffic system-services ? Possible completions:
all All system services
any-service Enable services on entire port range dns DNS and DNS-proxy service
finger Finger service ftp FTP
http Web management service using HTTP
https Web management service using HTTP secured by SSL ident-reset Send back TCP RST to IDENT request for port 113 ike Internet Key Exchange
lsping Label Switched Path ping service netconf NETCONF service
ntp Network Time Protocol service
ping Internet Control Message Protocol echo requests reverse-ssh Reverse SSH service
reverse-telnet Reverse telnet service rlogin Rlogin service
rpm Real-time performance monitoring rsh Rsh service
sip Enable Session Initiation Protocol service snmp Simple Network Management Protocol service snmp-trap Simple Network Management Protocol traps ssh SSH service
telnet Telnet service tftp TFTP
traceroute Traceroute service
xnm-clear-text JUNOScript API for unencrypted traffic over TCP xnm-ssl JUNOScript API service over SSL
You can specify any of the following protocols: [edit security zones]
user@host# set security-zone HR host-inbound-traffic protocols ? Possible completions:
all All protocols
bfd Bidirectional Forwarding Detection bgp Border Gateway Protocol
dvmrp Distance Vector Multicast Routing Protocol igmp Internet Group Management Protocol
ldp Label Distribution Protocol
msdp Multicast Source Discovery Protocol nhrp Next Hop Resolution Protocol
rip Routing Information Protocol router-discovery Router Discovery
rsvp Resource Reservation Protocol sap Session Announcement Protocol vrrp Virtual Router Redundancy Protocol
Specifying Types of Traffic Permitted into the Device: Part 3
You can specify allowed traffic either at the zone level of configuration or the interface level within a zone. As with any configuration in the Junos OS, the precedence rule of more specific configuration applies here as well. In other words, interface-level configuration (as it is more specific) overrides the zone-level configuration. In the examples on the graphic, only HTTP system services are allowed into interface ge-0/0/1, which is part of the HR Zone. All other interfaces associated with the HR Zone can accept all system services.
Check Your Knowledge: Part 1
The graphic shows an example of zone configuration. What types of traffic are allowed into the specified zone and interfaces?
Check Your Knowledge: Part 3
The graphic shows the third example in this series. What does this configuration do?
Monitoring Zones
The graphic illustrates the show security zones command, which is useful for zone monitoring. The command provides information on the zone type and name along with the number and names of interfaces bound to the zone.
Using the show interfaces interface-name extensive command enables you to view zone specifics. The command displays information on permitted protocols and system services allowed into the device through the corresponding interfaces. In addition, the command provides information on flow statistics through the interface.
Monitoring Traffic Permitted Into Interfaces: Part 2
The graphic provides the continuation of the output from the previous page.
Review Questions
Answers
1.
A zone is a collection of one or more network segments sharing identical security requirements. 2.
Overall, there are two types of zones in the Junos OS—user-defined and system-defined zones. User-defined zones include security and functional zones, both of which you can configure. The Null Zone is a system-defined zone that you cannot configure. The security zone facilitates transit packets and packets to the device itself. The functional zone facilitates only management traffic. The Null Zone is a placeholder for interfaces that do not belong to any zone. All interfaces belonging to the Null Zone drop all packets.
3.
To configure a zone, you must perform the following steps: (1) Define a security zone or a functional zone; (2) Add logical interfaces to the zone; and (3) Optionally, add services and protocols that must be permitted into the device.
4.
Chapter 3: Security Policies
This Chapter Discusses:
• Security policy functionality; • Components of a security policy;
• Verification and monitoring of security policies; and • Configuring a security policy.
What Is a Security Policy?
A security policy is a set of statements that controls traffic from a specified source to a specified destination using a specified service. If a packet arrives that matches those specifications, the SRX Series device performs the action specified in the policy.
Network security policies are highly valuable for secure network functionality. Network security policies outline all network resources within a business and the required security level for each resource. The Junos operating system provides a set of tools to implement a network security policy within your organization. Security policies enforce a set of rules for transit traffic, identifying which traffic can pass through the firewall and the actions taken on the traffic as it passes through the firewall.
Review: Packet Flow
The graphic reviews packet flow through the flow module of a Junos security platform.
When the device examines the first packet of a flow, based on incoming and outgoing zones, it determines the corresponding security policy, and it performs a security policy lookup. The system checks the packet against defined policies to determine how to treat the packet.
In this material, we focus on the security policies portion of the Junos OS.
Transit Traffic Examination
The Junos OS for security platforms always examines transit traffic by using security policies. As illustrated on the graphic, should no match exist in the security policy, the default security policy applies to the packet. We highlight the default security policy in a subsequent graphic.
host-inbound-traffic Examination
If the destination of traffic is the device’s incoming interface, security policies are not applicable. The only examination that takes place is the list of services and protocols allowed into that interface using the
host-inbound-traffic statement within a zone definition.
The Junos OS examines security policies if the traffic destination is any interface other than the incoming interface. This process is true regardless of whether the incoming interface and the destination interface are in the same zone (intrazone traffic) or in different zones (interzone traffic).
The flowchart on the graphic illustrates the order of packet examination. When the device receives traffic destined to itself, it first examines whether the destination of the traffic is the incoming interface. If so, it skips the policy examination. Otherwise, the corresponding security policies evaluate the traffic. If no policy match exists for the traffic, the default policy action applies. We discuss the default security policy next. If traffic matches a security policy that permits it, the device then examines the list of services and protocols allowed into the destination interface within the corresponding zone, and applies the corresponding action.
System-Default Security Policy
By default, the Junos OS denies all traffic through an SRX Series device. In fact, an implicit default security policy exists that denies all packets. You can change this behavior by configuring a standard security policy that permits certain types of traffic, or by configuring the default policy to permit all traffic as shown in the following screen capture.
[edit security policies]
user@host# set default-policy permit-all [edit security policies]
user@host#
Factory-Default Security Policies
The factory-default template configuration file in branch security platforms has three preconfigured security policies (not to be confused with the system-default security policy discussed in the previous paragraph):
1. Trust-to-trust zone policy: Permits all intrazone traffic within the trust zone;
2. Trust-to-untrust zone policy: Permits all traffic from the trust zone to the untrust zone; and
Security Policy Conceptual Example
We now examine an example of a packet flow through a Junos security platform.
The device’s interfaces are separated into three security zones—private, external, and public. The business
requirement calls for an SSH application to be allowed from Host B, located in the private zone, to Host D, located in the external zone. To meet the requirement, we created the security policy illustrated on the graphic.
The following is the sequence of events that takes place: 1. Host B initiates the SSH session to Host D.
2. The Junos security device receives traffic and examines it using its security policy from the private zone to the external zone. The security policy permits that traffic.
3. The Host B-to-Host D flow triggers the creation of the reverse flow from Host D to Host B. The graphic identifies the contents of this newly formed session. It consists of two flows—source to destination and destination to source.
4. Host D sends the return traffic, from Host D to Host B. The device, using a pre-created session, permits the return traffic through to Host B.
Policy Ordering
Because policies execute in the order of their appearance in the configuration file, you should be aware of the following:
• Policy order is important.
• New policies go to the end of the policy list.
Editing Security Configurations
Like any other Junos configuration stanza, you can delete, deactivate, activate, insert, annotate, and
copy security policies.
Security Policy Contexts
When defining a policy, you must associate it with a source zone, or incoming zone—named the from-zone. Also, you must define a destination zone, or an outgoing zone—named the to-zone. Within a direction of source and
destination zones, you can define more than one policy, referred to as an ordered set of policies, which the Junos OS executes in the order of their configuration.
Recall that a zone is a collection of multiple logical interfaces with identical security requirements. The Junos OS always checks all transit traffic—intrazone and interzone—through the use of security policies.
Security Policy Components
Within the defined context title, each policy is labeled with a user-defined name. Under the user-defined name is a list of matching criteria and specified actions, similar to a Junos routing policy. One major difference is that each security policy must contain a matching source address, destination address, and application. Actions for traffic matching the specified criteria include permit, deny, reject, log, or count.
The Junos OS also uses policy to invoke the use of Intrusion Detection and Prevention (IDP) policies, the Unified Thread Management (UTM) feature for branch devices, and firewall authentication.
Policy Match Criteria
Each of the defined policies must include the following matching criteria:
• Source addresses: This criterion can be in the form of address sets or individual addresses. You can
group individual addresses into address sets.
• Destination addresses: This criterion can be in the form of an address sets or individual addresses. You
can group individual addresses into address sets.
• Applications or application sets: This criterion can be user-defined or system-defined. The Junos OS
supports system-crafted default applications and application sets, referred to using the format junos-application, where application is the name of the actual application. You can also define your own applications.
You must specify all matching components. If you omit any of these components, the Junos OS will not allow you to commit the configuration.
Creating Address Book Entries
The graphic illustrates the syntax that you must use when creating address book entries. An address book within a zone can consist of individual addresses or address sets. An address set is a set of one or more addresses defined within an address book. Address sets are useful when you must refer to a group of addresses more than once. If the matching criteria needs no specific address, no address book entry is necessary. In this case, you can specify the configuration option any as the source or destination address in a security policy.
Defining Custom Applications
The Junos OS has many built-in applications, such as junos-rsh, junos-sip, junos-bgp, and so forth. You can customize the list of predefined applications (thus expanding the overall list), which gives you the capability to support complex applications.
user@host> top show groups junos-defaults | match application | match junos application junos-ftp {
application junos-ssh { application junos-telnet { ...
To configure a custom application, define the application name, associate the application with a protocol and ports. Use the application-protocol configuration option to associate the custom application with an
application-level gateway (ALG). A user-configured application has a timeout value associated with it. The Junos OS applies the timeout value to the created session. Once the timeout expires, the software clears the session from the session table. You can modify the timeout value for a specific application. Note that the new timeout value applies only to new sessions—not to existing ones.
Creating Policy Match Entries
You enter all policies under the from-zone...to-zone stanza for that particular traffic direction. The
from-zone...to-zone stanza associates the policies under it with a source zone and a destination zone. Under a specific zone direction, each security policy contains a name, match criteria, and an action. This example focuses on match criteria. The system executes all policies in the order of their appearance within a configuration file.
Basic Policy Actions
Each policy has a list of basic and advanced actions associated with it. The basic actions are the following: • permit: Allows traffic flow;
• deny: Results in a silent packet drop; and
• reject: Results in a packet drop and the sending of an Internet Control Message Protocol (ICMP) unreachable message for UDP traffic and a TCP reset register suppression time (RST) message for TCP traffic.
Log and Count Traffic
For each of these actions, you can configure the Junos OS to log and count traffic as well. To view counters, use the
show security policies detail operational mode command.
Advanced Permit Settings
Among the policy actions mentioned on the previous section, the following advanced permit settings exist: • Firewall authentication;
• IDP; and • UTM features.
Firewall authentication enables you to restrict and permit users accessing protected resources that could be located in different zones. The Junos OS offers two methods of firewall authentication:
• Pass-through: Firewall users that are using FTP, Telnet, or the Hypertext Transfer Protocol (HTTP) to
access protected resources across the device receive authentication through a username and password. The Junos security platform intercepts the session and then performs user authentication. • Web authentication: Firewall users use HTTP or HTTP over Secure Sockets Layer (HTTPS) to access an
IP address of the Junos security device, instead of the protected resource. The device acts as a proxy, authenticating the user with a username and password and caches the information.
We discuss firewall authentication in more detail in “Firewall User Authentication.”
If a policy associates with a preconfigured IPsec VPN tunnel, the tunnel creation occurs dynamically upon the receipt of the first packet that matches such a policy. The policy-based IPsec VPN can be one of two types—IKE or manual. We discuss IPsec VPNs in more detail in “IPsec VPNs.”
A policy can associate with an IDP policy. IDP policies inspect traffic and enforce various attack detection and prevention techniques. We discuss IDP in more detail in “Introduction to IDP”.
In branch devices only, a policy can also associate traffic with UTM features such as antivirus, content filtering, and Web filtering.
Policy Components Summary
The following is a summary of the policy components:
• A security policy is positioned within the from-zone and the to-zone direction of traffic within configuration;
• Each policy has a set of matching conditions;
Control Plane Logging
The Junos OS logs control plane events either locally or to an external syslog device. Locally stored logs are stored on the Routing Engine under the /var/log directory; you can view them by using the show log log-name operational mode command. To configure logs to be sent to an external syslog server, use the host configuration option. The example on the graphic shows the control plane logging statements present in a factory-default configuration.
Branch Device Data Plane Logging
Data plane logging in Junos security platforms for the branch can be stored locally or on an external system log (syslog) server. Use the session-close and session-init configuration options within a security policy to log the start and close of sessions matching a policy. We suggest to use only session-close on production devices. Logging both session-close and session-init will cause high CPU utilization on some SRX Series devices for the branch.
The graphic illustrates a sample log file configuration for branch devices. Logs are stored locally in the /var/log directory when designated with a filename. To send logs to an external device, use the host IP address configuration option.
The default facility and severity for data plane session logging is user info. To enable a Network and Security Manager (NSM) device to be able to retrieve logs, name the log file default-log-messages, as shown on the graphic, and include the structured-data configuration option.
High-End SRX Series Data Plane Logging
Data plane logging in high-end SRX Series devices can go to an external syslog device. The Junos OS supports limited local data plane logging because of the high volume of session handling that a high-end SRX Series device supports. The graphic illustrates the configuration of data plane logging for high-end SRX Series devices.
Currently, the Junos OS supports one stream of logging traffic. Supported collection devices include UNIX syslogd-based servers and the Juniper Networks Series Security Threat Response Manager (STRM).
Logging Sessions in Security Policy
Use the session-close and session-init configuration options to log the start and close of sessions matching a policy. The graphic illustrates the configuration of the policy log action.
Collecting Security Policy Statistics
Use the count security policy action to collect statistics and make them available using operational show commands. The count security policy action is not necessary to enable statistics collection in security policy logs. Logs containing session-close messages contain statistics by default.
Operational Monitoring Commands
Various show commands are available for monitoring the application of security policy. The show security
policies command allows you to view details about an applied policy such as the policy index number, policy
matching conditions, and policy actions. Use the detail command option to view statistics associated with policy counters.
The show security flow session command displays active sessions on the device and each session’s associated security policy. Note that this command output is categorized per Services Processing Unit (SPU) application-specific integrated circuit (ASIC). The following output is from a services gateway containing two services processing cards (SPCs) and therefore, four total SPUs. Only one session is active on the services gateway:
user@host> show security flow session 0 sessions displayed
0 sessions displayed 0 sessions displayed
Session ID: 210000935, Policy name: permit-ftp/5, Timeout: 1768 In: 10.100.0.2/50054 --> 10.200.1.2/21;tcp, If: ge-1/2/1.10 Out: 10.200.1.2/21 --> 10.100.0.2/50054;tcp, If: ge-1/0/1.40 1 sessions displayed
Tracing Security Policy
The configuration shown on the graphic enables the tracing of security policy evaluation and sessions on a Junos security platform. Use the packet-filter configuration option to log only details concerning selected sessions. Note that because of the architectural design of Juniper Networks security and routing platforms, you can enable reasonably detailed tracing in a production network without negative impact on overall performance or packet forwarding. However, a good practice would be to deactivate traceoptions when not troubleshooting the device to reduce the impact on system resources.
Policy Scheduling
A policy scheduler is a method for scheduling a policy execution for a specified duration or a set of durations. A policy scheduler is optional. A scheduler supports system time updates either through manual configuration or through the Network Time Protocol (NTP) by synchronizing itself with the time changes.
Rules for Scheduling
The following rules apply to policy scheduling:
• An individual policy can have only one scheduler applied; • Multiple policies can use the same scheduler; and
• A scheduler must be referenced in a policy to become active. Without a defined scheduler within a policy, the policy is always active.
Security Policy Scheduler Components
A security policy scheduler provides you with the flexibility to identify the start date and time and stop date and time for policy enforcement. In particular, the scheduler components include the following:
• Slot schedule: This component consists of the start date and time and the stop date and time of policy
enforcement; and
• Daily schedule: This component consists of the start time, the stop time, the all-day option, and the
exclude option.
Policy Scheduler Details
A policy scheduler turns on recurrently or once at the specified time. Recall that a policy scheduler activates and deactivates a policy according to the scheduled time, which you configure. Once you create the scheduler, you must apply it to a policy. The default behavior of a policy is to execute at all times.
Optionally Applying the policy-rematch Statement
The default behavior of the Junos OS is to not disturb sessions in progress when you make configuration changes to security policies. For example, you can modify an address field or modify the actions of a policy used for session examination. By default, because a session was pre-established, it continues to be operational without any
interruptions. You can change that default behavior by enabling the policy-rematch statement. Once you enable the statement, every time a configuration change to a policy occurs, it reflects in the sessions in progress.
Configuration changes, such as source addresses, destination addresses, and application changes, cause policy re-evaluation as the system performs a policy lookup. If the newly matched policy is not the policy referred to by the session, the session clears. If an IPsec VPN change occurs, the Junos security platform clears the session.
The following list explains the actions that the Junos OS performs on impacted sessions in progress based on whether the policy-rematch flag is enabled or disabled.
• When the policy-rematch flag is enabled: – The software inserts a policy: no impact;
– The software modifies the action field of a policy from permit to either deny or reject: all existing sessions are dropped; and
– The software modifies some combination of source address, destination addresses, and applications fields: the Junos OS re-evaluates policy lookup.
• When the policy-rematch flag is disabled (default behavior): – The software inserts a policy: no impact;
– The software modifies the action field of a policy from permit to either deny or reject: all existing sessions continue; and
– The software modifies some combination of source address, destination addresses, and applications fields: all existing sessions continue unchanged.
Note that irrespective of the value of policy-rematch policy flag, deletion of the policy causes the device to drop all impacted existing sessions.
