Header Only - DO NOT REMOVE - Extreme Networks

Stacking effect on STP&OSPF

  • 7 January 2014
  • 3 replies

Userlevel 4
Create Date: May 14 2013 10:42PM

I'm trying to design a new network we intend on building out. The current plan is to use X460's as access switches, have redundant links Layer 2 links from each access switch to the distribution layers switches which are X480's which operate as a stack (ie only one connection from each access switch to each distribution switch). We then want to connect each X480 to a single different Cisco core router and have OSPF running between them.

So my questions are

(1) Will STP work between the access switches and distribution switches so that only one link will be up at a time?.
(2) In the future we intend on load balancing different VLAN's across the redundant links between the access and distribution layer. Will this work too?
(3) Can an OSPF connection be formed between the two X480s across the stack cable?
(4) If this OSPF connection can't be formed between the 2 X480's will the two Cisco routers see them as a single device as well or as multiple devices?

(from ekelste)

3 replies

Userlevel 4
Create Date: May 14 2013 10:51PM

Network drawing attached
(from ekelste)
Userlevel 4
Create Date: May 15 2013 2:10AM

This setup will definitely work. What I have on my network is somewhat similar, and I'll provide my take on the questions here based on my experience with Extreme gear.

1) Yes. However, for Extremes in a ring config I'd recommend going with EAPS. EAPS reconverges faster and is easy to configure.
2) Yes. You can also use LAG (or MLAG, if you have more than 2 switches participating) to get the bandwidth of both links simultaneously while maintaining redundancy.
3) No. Stacked switches are managed as a single device. This has a lot of advantages, and as the switches in this case are the same models you can configure them to be fully redundant with no loss of functionality if there's a failure.
4) The Ciscos will see the X480 stack as a single device. (from Ansley_Barnes)
Userlevel 4
Create Date: May 15 2013 2:22AM

By the way, if you plan to have single access switches (logically - stacks count as single switches for this purpose) I would recommend going with LAG instead of STP or EAPS. This will provide the bandwidth of both links and maintain redundancy. For example:

On the X460:

enable sharing 51 grouping 51,52

On the X480 stack:

enable sharing 1:1 grouping 1:1, 2:1

Connect ports 51 and 52 on the X460 to ports 1:1 and 2:1 respectively on the X480 stack. Managing the link between the switches happens by addressing config changes to the first port referenced by "enable sharing," so you add VLANs to port 51 on the X460 and port 1:1 on the X480 stack, and the VLANs are added to all the links in the LAG. To balance the load on the links, if it is lopsided, you can adjust the load-sharing algorithm. X460s and X480s have highly configurable forwarding planes, so good choice on those! If a link is severed, unplugged, or one of the X480s fails, the other link stays up and provides full connectivity (albeit with half the bandwidth, of course.) This configuration also allows more links to be added to the LAG group easily and quickly, if your bandwidth needs grow.

EAPS works well, and STP would work, but if you can, I'd start with this config - it'll save the migration later and help prevent bottlenecks. If you must start with a ring, I strongly recommend EAPS over STP. (from Ansley_Barnes)