topic Route selection behavior of multiple default static routes in ExtremeSwitching (EXOS/Switch Engine)

Route selection behavior of multiple default static routes

KevinR — Wed, 08 May 2024 23:47:22 GMT

In EXOS, if you have multiple default routes with the same metric, then how is traffic split between them?

For example if you have the following

configure iproute add default 10.10.11.1
configure iproute add default 10.10.12.1

How will it choose a route for a connection? I'm assuming it's based on some hash of either/all source IP, destination IP and port. Is there a way to specify the hashing method? For example, based on source IP only, so a source IP will always use the same route?

I'm trying to share the load between two low bandwidth default routes. My concern is client sessions breaking if an application creates a connection to one IP and it uses default route 1, then client application creates another connection to different IP and it uses default route 2.

Or do I need to use PBR?

Re: Route selection behavior of multiple default static routes

Gabriel_G — Thu, 09 May 2024 15:52:24 GMT

Regarding the route selection process when there are multiple default routes:
1) The default route with the lowest metric is used.
2) If the metrics are equal, the default route with the lowest next hop IP is used.

If you want to load balance between multiple routes, you'd need to enable ECMP (enable iproute sharing). This allows routes of the same type with the same metric/cost to be installed simultaneously (as indicated by the 'f' flag in 'show iproute'). You can further configure the hashing algorithm with 'configure iproute sharing ...' commands.

You can read more on ECMP in the user guide, page 1492 and 1512.

https://documentation.extremenetworks.com/exos_31.7/downloads/EXOS_User_Guide_31.7.pdf