2 x 3750 stacked + 870 for WAN

[Pawel Lenart]

Hi all,

I have a question in regards to configuration I'm planning to implement. I currently have 2 x 3750 running in a stack. I would like to add 1 x 870 router connected to both switches.

It's important for me that 870 is always available (it will only be used as a backdoor for our management network through WAN) but I don't want it to participate in any switching (including switching for management network unless it's going through this backdoor WAN). My question is:

Do I need to configure spanning tree on all switches or stack is automaticly working as a 1 logical unit?

As router is only using 100MB/s connection, how I can prevent this router from switching packets with other switches?

Any tips in regards to this setup?

Kidn regards,

Pawel

[Leo Laohoo]

If the 870 will be used for OoBM, then the WAN goes to your internet provider.

One of the four LAN links will be on the same Management VLAN as the switches.   Careful with this because the 870, if running 12.4 IOS, can only support up to 4 VLANs. 

[Pawel Lenart]

Hi leolaohoo,

I already done this part. Do you have any feedback in regards to connecting router to both switches in the same time and spanning tree?

Regards,

Pawel

[shamax_1983]

Hello Pawel,

Technically I don't see any issues connecting two interfaces from the router to each stacked switch.

As I remember, 870 routers are running STP on all it's switchports and it lets you change the Bridge priority as you like. So you will have control over where you want your the root. Once done, stp will block ports appropprately and make it loop free.

Please rate this post if helpful

Shamal

[Pawel Lenart]

Hi Shamal, OK, I will test it tomorrow. Thank you very much.

[Leo Laohoo]

If both switches are stacked, then you can configure an etherchannel, however, I'm not sure if 870 LAN ports will support Etherchannel.

[Pawel Lenart]

No STP configration was required. Thanks for your feedback.