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Static and default routing question

With a simple dual link connection between two sites, and configuring two static and default routes, which route will be chosen or used by router-1 for known and unknown routes (with ip classless enabled):

[router-1]

E0: 10.10.10.1 255.255.255.0

S0: 192.168.1.1 255.255.255.252

S1: 192.168.1.5 255.255.255.252

ip route 20.20.20.0 255.255.255.0 192.168.1.2

ip route 20.20.20.0 255.255.255.0 192.168.1.6

ip route 0.0.0.0 0.0.0.0 192.168.1.2

ip route 0.0.0.0 0.0.0.0 192.168.1.6

[router-2]

E0: 20.20.20.1 255.255.255.0

S0: 192.168.1.2 255.255.255.252

S1: 192.168.1.6 255.255.255.252

ip route 10.10.10.0 255.255.255.0 192.168.1.1

ip route 10.10.10.0 255.255.255.0 192.168.1.5

Thank you for any input.

1 REPLY

Re: Static and default routing question

Hi,

Since both the above routes are having same administrative distance, both routes will get installed in the table. Which route will be used, again depends on type of switching configured on the interface.

By default most interface will have Fast switching enabled, which is a per-destination load balancing. Fast switching populates a cache, which is used for switching the packets, without referring to routing table repeatedly, for the same type of traffic flow.

Fast switching switches traffic based on destination. The first packet of a traffic flow from Host A on site A to Host B on site B will choose one of the above default routes (interfaces). For all traffic flows between hosts A and B, the same interface will be used ( as long as the flow entries are there in cache). For traffic from say Host A on site A to Host C on site B, the route chosen will be the second default route. ( route selection is a randomized process) This process is repeated, for every source destination pair.

For per packet load balancing, router will alternate between the above routes.

You should be having now the first type of LB, that is Per-destination LB.

Hope that helps!

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