options
• Is it possible to load balance between two ISP links? on page 1
• Does the ASA support PBR (Policy Based Routing)? on page 1
What other options do we have? on page 1
• SLA Route Tracking on page 1
• PBR on the router outside the firewall on page 2
• Allowing outbound via ISP1 and inbound via ISP2 on page 4
• Multiple context mode on page 5
Is it possible to load balance between two ISP
links?
Presently it is not possible to load balance traffic between two ISP links on an ASA. The reason being, there can only be one default route configured on the ASA.
Does the ASA support PBR (Policy Based
Routing)?
No, the ASA does not support PBR.
What other options do we have?
SLA Route Tracking
Refer this link: http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/ products_configuration_example09186a00806e880b.shtml
PBR on the router outside the firewall
With this method we can configure both the ISP links on the router outside the firewall. We can translate some traffic to use Primary ISP provided IP address and the rest of the traffic to use Secondary ISP provided IP address. Now, based on this source address that hits the router, we can configure the router to do policy based routing and route the traffic either via the Primary ISP or via the Secondary ISP.
Let us assume the requirement as below:
1. We would like all the users traffic translated to the ISP1 provided address 2. We would like all the servers traffic translated to the ISP2 provided address
ISP1 provided address block is 10.10.10.0/24 and ISP2 provided address block is
172.18.124.0/24. These are not routable addresses. For simplicity reasons we are using RFC 1918 address space.
ASA config:
Translation for all users to take ISP 1 nat (inside) 1 192.168.2.0 255.255.255.0 global (outside) 1 10.10.10.1
Translation for web and e-mail servers to take ISP2
static (inside,outside) 172.18.124.20 192.168.2.20 netmask 255.255.255.255 static (inside,outside) 172.18.124.30 192.168.2.30 netmask 255.255.255.255
route outside 0 0 172.16.12.2
Router config:
ip access-list ext isp1-addr
permit ip 10.10.10.0 0.0.0.255 any
ip access-list ext ips2-addr
permit ip 172.18.124.0 0.0.0.255 any
route-map ISP permit 20 match ip address isp2-addr set ip next-hop 172.18.124.2
int f0/0
ip address 172.16.12.2 255.255.255.0 ip policy route-map ISP in
Allowing outbound via ISP1 and inbound via ISP2
Let us take the same example above. We can use one ISP1 for all outbound connections and use IPS2 for all inbound connections.
Translation for all outbound connections from users and servers to take ISP 1 nat (inside) 1 192.168.2.0 255.255.255.0
global (ISP1) 1 10.10.10.1 route ISP1 0 0 10.10.10.254
Here are the translations for inbound connections to the servers: Translation for web and e-mail servers to take ISP2
In the previous case even the out bound connections made by the servers would take the ISP2 path but, in this example outbound connections from the web and e-mail servers will take ISP1. ONLY the INBOUND connections will come through ISP2 and will be responded back using ISP2.
Multiple context mode
The last option is to use multiple context mode where we can load balance on a per context basis. VPN is not supported in this mode and so are dynamic routing protocols. Please refer this link for the limitations: http://www.cisco.com/en/US/docs/security/asa/asa82/ configuration/guide/contexts.html#wp1146747
