Before I respond let me encourage you to post any furture questions/follow-ups on the forums; http://forums.networkinfrastructure.info/nortel-ethernet-switching/.

You can most certainly run Spanning Tree in an MLT configuration. You cannot run Spanning Tree in an SMLT configuration. I’ve made the personal decision to avoid using Spanning Tree where ever possible and instead rely on Layer 3 routing and Nortel’s proprietary IST/SMLT technology.

With respect to your specific configuration you can certainly enable and run STP between your closets and your core switch (you didn’t say what switch you had in the core). You only need to be mindful of how Nortel’s proprietary Spanning Tree works, unless you configure all your switches for RSTP or MSTP (you’ll need to make sure that your running a software version that supports RSTP and/or MSTP on both your core and edge switches). In short you need to align the ports in your MLT from the lowest ifNum to the highest ifNum. Example; port 1/48 on the 5520 connects to port 1/8 on the core while port 2/48 connects to port 2/8 on the core. If you were to cross those ports using Nortel’s proprietary Spanning Tree you would probably experience issues since Nortel only broadcasts BPDUs on one port (the lowest ifNum in the MLT) while other vendors like Cisco broadcast BPDUs on all ports in the EtherChannel (MLT).

You would definitely need to-do your homework though and make sure that you set the root bridge priority on your core switch properly. You might also need to tweak the STP path costs to make sure that the interconnects between your edge switches are the ports that go into blocking and not your MLT uplinks.

I’ve avoided such configuration because I believe it leads to overly complex networks that often tend to fail on their own or through some unforeseen circumstances. As an alternative you could also have ports configured and cables ready (just unplugged) such that if you had an actual disaster you could quickly wire up the ports to an alternate edge switch. It would require manually connecting the patch cables but it would restore you to service much faster than waiting for the cabling vendor to re-splice your fiber pairs.

Cheers!

Now if I would disable stp on the mlt ports, I would imagine it would create a loop and down the network goes…. anywho, i did my best to explain this…. hope it makes sense. let me know your thoughts when you have time.

Thanks!
Todd

I really appreciate the comment and I’m happy to hear that you found the information useful.

Cheers!

I just found your site today and have already forwarded it off to probably 10 people.

Thanks in advance for any solutions your provide me, I’ll be sure to give credit where credit is due!

In an SMLT configuration it’s best practice to enable SLPP on the edge ports at the core switch (not the edge switch).

I have an article that describes SLPP here;
http://blog.michaelfmcnamara.com/2007/12/simple-loop-prevention-protocol-slpp/

While SLPP is applicable it doesn’t get configured on the edge ERS5520 itself but rather on the core switch.

If you are running any of the ERS 5500 series switches in a Layer 3 configuration with the Advanced Routing License then those switches themselves can act as core switches as opposed to just being a Layer 2 edge switch.

Thanks for the comment!

I had thought I replied to your post (perhaps you posted in the forums?) but I see you have a reply here without any response… sorry for that.

I’m guessing that when you enable the Access Policy your not making allowances in the policy for the server/desktop running MRTG to be allowed to perform SNMP queries against the switch.

Have a look at this post for an example of how to configure an Access Policy; http://blog.michaelfmcnamara.com/2008/01/ers-8600-access-policy/

Good Luck!

Very interesting… thanks for the post!

Mike