Switch - Switch Layer 3 connectivity

[Bab L]

Hi.

We have two switches in diffrent buidling connected via fibre.

For some reason, the design states that the switches will need to be configured with Lyaer 3 connectivity and redundnuncy.

So, at on e end we have the core switch with two interfaces configured as a port channel with an ip address.

On the other end one interface goes to one switch and one to the other.

Then, the two switches in the other end are connected with fibre.

The port channel IP is 172.16.255.249/29 in the core, 172.16.255.250/29 on one switch and 172.16.255.252/29 on the other.

We can ping 172.16.255.252 just fine, but we cant ping 172.16.255.250 from the core switch. Is this normal? We are trying to get redundancy going so if one switch fails traffic will be routed via the other.

Thank you

[Reza Sharifi]

Hi,

On the other end one interface goes to one switch and one to the other.

As long as both switches are stacked or in VSS, ping should work, if not the Portchannel will not come up and so ping does not work either.

HTH

[Jon Marshall · Accepted solution]

You can't do this ie. have a port channel interface at end but then separate interfaces on different switches with their own IPs on the other end.

The two switches in the other building, what model switch are they ?  I ask because you may be able to stack them or use some sort of virtualisation but it depends  on the models.

Alternatively don't use a port channel at all, just have two individual links each with their own addressing.

Jon

[Bab L]

Ok. What you say makes sense.

The core switch is 6807 and the other switches are 2960s.

So, what you're saying is remove the port channel from the core and just give each port an ip address connected to the other switches. Can they still be in the same subnet? Woould there be a routing loop?

[Jon Marshall]

You may be able to stack the 2960s and then terminate the etherchannel between the two switches although depends on your models and obviously how close they are to each other etc.

There is no mention of L3 etherchannels in the configuration guide that I can find but you just use a vlan and an SVI.

Or yes you could simply remove the port channel and have two separate links. You would want separate subnets per link but you only need two IPs per link.

It's not exactly clear what is routing what though ie. if the design calls for L3 connectivity what is being routed on the 2960s and do they route between each other as well as to the 6800 ?

Jon

[Bab L]

Thanks for your help everyone. Much appreciated.

I will remove the port channel and create a /30 for each interface connectivity.

Then I just use two static routes from the core using one backup static route.

[Reza Sharifi · Accepted solution]

So, what you're saying is remove the port channel from the core and just give each port an ip address connected to the other switches. Can they still be in the same subnet? Woould there be a routing loop?

If you can stack the switches, you can continue using the L-2 Portchannel with no issues.

If not  and as Jon said, you need to turn each link to a later-3 link which means you need to /30s.(one for each link).  Also, 2960s series is mainly a layer-2 switch and does not support routed interfaces, so you have to use 2  SVIs with IPs and use vlans.  Stacking them is the simplest solution.

HTH