Routing

Hi Experts

Attached is the topology,

One thing, I am facing and I am unable to solve it yet. The subnet 10.100.0.8/30 which is in between R4 and R1 and it is directly connected route of R4. When I leaked this subnet in to the L1 level using route leak policy on R4. I observed the below:

1- On R8 (other route leaking router), the subnet 10.100.0.8/30 is learned via L2 level and optimal route to reach this subnet should be R8-R4
2- On R8, the subnet 10.100.0.8/30 is also learned via L1 level and route to reach this subnet is R8-R5-R4 (which is suboptimal as compared to above one)

R8 just showing the route via L1 level because L1 routes are more preferred to L2 routes. So it is leading to suboptimal routing. Also same true for the subnet 10.100.0.4/30  which is in between R8 and R2 and R8 is leaking this directly connected routes in to L1 Level.

Appreciated your help.

Thanks

Attachment(s)

ISIS route leak .pdf   82 KB 1 version

Better make the link between R4-R8 to be L1/L2, and it'll solve the problem.

Thanks for the reply. There is no other solution like some knob of ISIS when leak this direct connected route from L2 to L1 level?

There's another solution to this problem although it may create other problems (even bigger).

You can change the router preference for the L1 on the R8:

set protocols isis level 1 preference 19

Thanks but I think it is creating suboptimal routing for more subnets 🙂 .....so I believe its the behaviour of ISIS when we leak routes from L2 level in to L1 level using two distributuion routers.