Link Layer Discovery Protocol

Link Layer Discovery Protocol (LLDP) is a vendor-independent protocol for network devices to advertise information about their identity and capabilities. It is referred to as

Station and

Media Access Control Connectivity Discovery

, which is specified in the 802.1ab standard. With LLDP and Link Layer Discovery Protocol–Media Endpoint Discovery (LLDP-MED), network devices can learn and distribute device information about network links. With this information, the switch can quickly identify various devices, resulting in a LAN that interoperates smoothly and efficiently.

LLDP-capable devices transmit information in Type Length Value (TLV) messages to neighbor devices. Device information can include specifics such as chassis and port identification, and system name and system capabilities.

LLDP-MED goes one step further, exchanging IP-telephony messages between the switch and the IP telephone. These TLV messages provide detailed information about the

Power over Ethernet (PoE) policy. With the PoE Management TLVs, the switch ports can advertise the power level and power priority that is needed. For example, the switch can compare the power that is needed by an IP telephone that is running on a PoE interface with available resources. If the switch cannot meet the resources that are required by the IP telephone, the switch can negotiate with the telephone until a compromise on power is reached.

The switch also uses these protocols to ensure that voice traffic gets tagged and prioritized with the correct values at the source itself. For example, the 802.1p class of service (COS) and 802.1Q tag information can be sent to the IP telephone.

4.1.12 Link Layer Discovery Protocol Type Length Values (LLDP TLVs)

The basic TLVs include the following information:

Chassis identifier The MAC address that is associated with the local system.

Port identifier The port identification for the specified port in the local system.

Port description The user-configured port description. This description can be a maximum of 256 characters.

System name The user-configured name of the local system. The system name can be a maximum of 256 characters.

Chapter 4. Ethernet and system networking concepts 77

Additional 802.3 TLVs include the following details:

Power via MDI A TLV that advertises MDI power support, a Power Sourcing Equipment (PSE) power pair, and power class information.

MAC/PHY configuration status

A TLV that advertises information about the physical interface, such as auto-negotiation status, support, and MAU type. The information is not configurable, but based on the physical interface structure.

Link aggregation A TLV that advertises if the port is aggregated and its aggregated port ID.

Maximum frame size A TLV that advertises the maximum transmission unit (MTU) of the

interface that is sending LLDP frames.

Port VLAN A TLV that advertises the VLAN name that is configured on the interface.

LLDP-MED provides the following TLVs:

LLDP MED capabilities

A TLV that advertises the primary function of the port. The capability values range 0 - 15. The device class values range 0 - 255:

0 . . . Capabilities 1 . . . Network policy 2 . . . Location identification

3 . . . Extended power via MDI-PSE 4 . . . Inventory

5 through 15 . . . Reserved LLDP-MED device class values

0 . . . Class not defined 1 . . . Class 1 device 2 . . . Class 2 device 3 . . . Class 3 device

4 . . . Network connectivity device 5 through 255 . . Reserved

Network policy A TLV that advertises the port VLAN configuration and associated Layer 2 and Layer 3 attributes. Attributes include the policy identifier, application types such as voice or streaming video, 802.1Q VLAN tagging, 802.1p priority bits, and Diffserv code points.

Endpoint location A TLV that advertises the physical location of the endpoint.

Extended power via MDI

A TLV that advertises the power type, power source, power priority, and power value of the port. It is the responsibility of the PSE device (network connectivity device) to advertise the power priority on a port.

4.2 Storage area network IP networking

Now that we introduced the protocols at a high level, what are the strategic differences between them all? Do I need them all, any, or none? What are some of the benefits that these technologies can bring me? The following list provides just some of the benefits you can gain:

򐂰 Departmental isolation and resource sharing alleviation

򐂰 Technology migration and integration

򐂰 Remote replication of disk systems

򐂰 Remote access to disk and tape systems

򐂰 Low-cost connection to storage area networks (SANs)

򐂰 Inter-fabric routing

򐂰 Overcoming distance limitations

People do not want to make a large financial investment without any guarantees that there will be some form of return. However, the appeal of these protocols is that they immediately bring benefits. Because these are standards-based protocols, they allow the use of both the existing TCP/IP and FCP infrastructure, they support existing Fibre Channel devices, and enable simplification of the infrastructure by removing any SAN islands.

4.2.1 The multiprotocol environment

As with any technology, it comes with its unique jargon and terminology. Typically it is borrowed from the networking world, but might have a different meaning. It is not our intent to cover every unique description. However, we do make some distinctions that we believe are important for a basic introduction to routing in an IP SAN.

4.2.2 Fibre Channel switching

A Fibre Channel

switch

filters and forwards packets between Fibre Channel connections on the

same

fabric, but it cannot transmit packets between fabrics. As soon as you join two switches together, you merge the two fabrics into a single fabric with one set of fabric services.

4.2.3 Fibre Channel routing

A

router

forwards data packets

between

two or more fabrics. Routers use headers and forwarding tables to determine the best path for forwarding the packets.

Separate fabrics each have their own addressing schemes. When they are joined by a router, there must be a way to translate the addresses between the two fabrics. This mechanism is called

network address translation

(NAT) and is inherent in all the IBM System Storage multiprotocol switch/router products. NAT is sometimes referred to as

FC-NAT

to differentiate

Chapter 4. Ethernet and system networking concepts 79

4.2.5 Routers and gateways

When a Fibre Channel router needs to provide protocol conversion or tunneling services, it is a

gateway

rather than a router. However, it is common usage to broaden the term

router

to include these functions. FCIP is an example of tunneling, while Internet Small Computer System Interface (iSCSI) and Internet Fibre Channel Protocol (iFCP) are examples of protocol conversion.

4.2.6 Internet Storage Name Service

The Internet Storage Name Service (iSNS) protocol facilitates automated discovery, management, and configuration of iSCSI and Fibre Channel devices that exist on an

IP network. iSNS provides storage discovery and management services comparable to those that are found in Fibre Channel networks. What this means is that the IP network seems to operate in a similar capacity as a SAN. Coupling this capability with its ability to emulate Fibre Channel fabric services, iSNS allows for a transparent integration of IP and Fibre Channel networks. This integration is possible because it can manage both iSCSI and Fibre Channel devices.

4.3 Delving deeper into the protocols

We introduced all of the protocols at a high level. Now, in greater depth, we show the method of what they do with the Fibre Channel traffic.

4.3.1 Fibre Channel over Internet Protocol (FCIP)

FCIP is a method for tunneling Fibre Channel packets through an IP network. FCIP

encapsulates Fibre Channel block data and transports it over a TCP socket, or tunnel. TCP/IP services are used to establish connectivity between remote devices. The Fibre Channel packets are not altered in any way. They are simply encapsulated in IP and transmitted. Figure 4-10 shows FCIP tunneling, assuming that the Fibre Channel packet is small enough to fit inside a single IP packet.

Figure 4-10 FCIP encapsulates the Fibre Channel frame into IP packets

IP payload (FC frame)

IP

Hdr

CRC

SOF

_HdrFC

SCSI data

CRC EOF

Fibre Channel frame

The main advantage of FCIP is that it overcomes the distance limitations of basic Fibre Channel. It also enables geographically distributed devices to be linked by using the existing IP infrastructure, while it keeps the fabric services intact.

The architecture of FCIP is outlined in the Internet Engineering Task Force (IETF) Request for Comments (RFC) 3821, “Fibre Channel over TCP/IP (FCIP)”, available at this website:

http://ietf.org/rfc/rfc3821.txt

Because FCIP simply tunnels Fibre Channel, creating an FCIP link is like creating an ISL. And, the two fabrics at either end are merged into a single fabric. This merge creates issues in situations where you do not want to merge the two fabrics for business reasons, or where the link connection is prone to occasional fluctuations.

Many corporate IP links are robust, but it can be difficult to be sure because traditional IP-based applications tend to be retry-tolerant. Fibre Channel fabric services are not as retry-tolerant. Each time the link disappears or reappears, the switches renegotiate and the fabric is reconfigured.

By combining FCIP with FC-FC routing, the two fabrics can be left “unmerged”, each with its own separate Fibre Channel services.

In document Introduction to Storage Area Networks (Page 96-100)