Nexus 5596T connecting to 3comm 5500

[rramlal]

Good Day all,

I have a query. Our customer will be changing out their 3comm core switch and placing in a nexus 5596 switch instead. There access switches will now be connecting to the 2 5596T switches that will be clustered.

Can a single 3comm switch be configured to connect two ports, one to each 5k? And will aggregating the  two ports on the 3comm end allow an active, active link to both 5ks?

Virtual port channels are supported on nexus 2ks and this can be used to connect to both nexus 5ks however will a 3comm allow this? I think it should be therethorically the 2 5ks are clustered and will be seen as one towards the 3comm.

What are your thoughts?

[Steve Fuller]

Hi,

As long as the 3Com switch supports IEEE 802.1AX (802.3ad) Link Aggregation then you're able to connect it with one link to each of a pair of Nexus 5596 configured with vPC. When running vPC the Nexus switches appear to the partner device as a single switch as it uses one Link Aggregation ID (LAGID) on both physical connections. In this way the partner device has no knowledge that it is connected to two physical devices.

The two links on the 3Com switch will be active and forwarding/receiving traffic. Traffic from the Nexus 5000 to the 3Com switch will be balanced across the two links based on the configuration of the port-channel load-balance ethernet command. Traffic from the 3COM to the Nexus will be balanced across the links based on the load-balancing algorithm available on that platform.

Hope that helps.

Regards

[rramlal]

Hi,

I finally got the nexus 5596ts and a 3com 5500. I configured vpc 12 on both nexus 5596 and connected this to the 3com switch. the port channel is not coming up on the nexus and on the 3com side when a "display stp brief" is done i am seeing one of the links as blocking and one as forwarding. this configuration didnt include port channeling on the 3com.

When port channeling is performed on the 3com end one of the links goes down.

The same steps were performed on a cisco 3560 and it worked perfectly so i am not certain whats different with the 3com. The 3com support link aggregation however runs rstp vs rapid pvst that is on the nexus. will this be a problem?

Furthermore, if both nexus are clustered then this is seen as one switch to the access switch and if two links are connected both ends will need to be port channeled to allow stp to take effect.....this is my thinking. i am certain why it is not working for the nexus and 3com, and why it is working with the nexus and cisco 3560.

any thoughts?

[Steve Fuller]

Hi,

the port channel is not coming up on the nexus and on the 3com side when a "display stp brief" is done i am seeing one of the links as blocking and one as forwarding. this configuration didnt include port channeling on the 3com.

Depends upon how the port-channel on the Nexus is configured, but I would say that's expected behaviour. If the 3COM isn't configured for link aggregation the Nexus port-channel is not receiving LACPDU so the ports would go into an Individual state. I expect if you ran the show port-channel summary command on the Nexus you would have seen the Individual (I) flag set for the two interfaces.

When port channeling is performed on the 3com end one of the links goes down. The same steps were performed on a cisco 3560 and it worked perfectly so i am not certain whats different with the 3com.

So how is the port-channel on the Nexus configured? On the physical interfaces are you using the command channel-group 12 mode active(dynamic LAG with LACP) or simply channel-group 12 (static LAG)?

Can you paste the output of a show port-channel summary, show lacp counters and show lacp neighbor? Also any log messages that are displayed on the Nexus when the link goes down would be useful.

Regards

[rramlal]

Hi

I was able to get this working. The port channeling was needed on both ends on the 3com and the nexus. Thanks much and sorry for the late reply.