Route overlap

[mbillilester]

I am running into an issue on cisco NCS (probably not an issue and is the intended behaviour)

I have multiple /24s that are all used for a cloud cluster and the vm inside the cluster uses .1 of each /24 for gateway, so i have made a BVI and have added the first ip (.1) with /24 subnet to the BVI.

But we have also taken some more specific prefixes out of these /24s such as /31s, /29s that we have allocated to bare metal users over vlan sub interfaces (i assign the first ip on the vlan interface on the router side that the client nodes use for gateway).

This setup is working perfectly fine on our DPDK based router but now we are planning to move to cisco, when i bring up the subinterfaces, the “show route” doesnt include the /24 route for BVI 1. If the subinterfaces (that have the ips with less specific subnets assigned) are in a down state the /24s on the BVI works perfectly.

It is not practical for me to change the routing scheme for the end users since there are thousand of users (VMs are Bare metals) on the network with these settings configured.

[Harold Ritter]

Hi @mbillilester ,

It would definitely help to have some kind of diagram and also the configuration you are trying to implement on the NCS.

[Joshqun Ismayilov]

Hi @mbillilester 

I think it is happened becuase Routing always uses longest prefix match. If the router has directly connected /29 or /31 interfaces it will install more specific connected routes / I hope it will be solution - make the subinterfaces L2 and let the BVI be the single gateway or another way force the /24 into the RIB with a static route.

Thanks !

[MHM Cisco World]

What you need is partition the /24 

Then extract /31 and /29 

The remaining subnet /x you can use it for BVI

MHM

[srimal99]

Worth checking for ip conflict, could be the reason to BVI and subinterface are down or vice versa.