STP redundancy 2900 Switch

[Tippey]

Hello, 

Just a quick one as my head is getting a little confused now.

We currently have a 2900 switch with a trunk currently setup to allow a number of VLAN's to a customer maintained switch.

We are wanting to setup another trunk on our switch going to the same customer switch.

Just checking to see what the best setup would be, or would STP work this out on its own?

Thanks in advance

[Reza Sharifi]

Hi,

Once you setup the second link, stp will block one of them since you will have redundant links and if stp is enabled. The other option would be to put both links in a Portchannel, this way you can use both links and there is no blocking since both links logically become one.

Link to config guide:

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/12-2_53_se/configuration/guide/2960scg/swethchl.html

HTH

[Tippey]

Thanks for the reply, customer wants to avoid the channel route, i did believe this would probably be the better option.

I assume in regards to the STP, both trunks would have the same config ie same native and same allowed vlans applied and then STP will just work its magic?

[Reza Sharifi]

I assume in regards to the STP, both trunks would have the same config ie same native and same allowed vlans applied and then STP will just work its magic?

That is correct as long as STP is not disabled for some reason.

HTH

[Joseph W. Doherty]

As already answered by Reza, the answer is yes, i.e. STP should do it's "magic".

However, two points to consider. First if using STP, you should reconsider whether to use RSTP. Second, as you have multiple VLANs, by default, STP will block the same port on all VLANs. As Cisco supports per-VLAN STP, you have the option to "tweak" STP such that different VLANs will block different trunk ports. This allows you to configure which trunk links a VLAN will use when there are more than one.

[Martin L]

one way that makes sense is channel port (Portchannel) and perhaps best way. if one of links fails , u still have another one. I think we can have up to 8 links in Portchannel