OSPF and ASA 5500

brukerbiospin · ‎06-10-2009

I have an ASA 5500 connected to two routers on an MPLS network (T1 on each router). We have configured the ASA to use OSPF to distribute the traffic over the MPLS network. This seems to be working fine for data, but we also want to use this network for VoIP. One item we are having a difficult time tracking down is how the ASA handles OSPF is it per packet or per session? The MPLS network is designed as a per session.

Giuseppe Larosa · ‎06-10-2009

Hello Ed,

your question could be restated in the following manner:

does the ASA perfom per flow load balancing or per packet load balancing ?

As in a router OSPF duties finish with the discovery of two equal cost paths to an IP destination.

How the two paths are used is a different matter and depends from the switching strategy.

It should be flow based in an ASA because it is a stateful firewall.

See the section

Next Hop selection process

in

http://www.cisco.com/en/US/docs/security/asa/asa80/configuration/guide/ip.html#wp1118250

load balancing works if both next-hops are out the same interface.

Hope to help

Giuseppe