Recommended Method of Connecting Single Switch to vIST pair of switches (SMLT/MLT?)

[cemcjk]

Hello, 

I'm new to VOSS/Fabric Engine and having some trouble understanding the way to uplink a single switch to multiple switches (redundant physical links, single logical link). I have 4 VSP7432 switches interconnected, two pairs of vISTs.

Just focusing on a single pair though, I'm trying to figure out how to connect a 5520 running VOSS using it's QSFP ports to one port on each of the 7432s. I have 1/25-1/26 on the 5520 configured in an MLT, with isis/spbm enabled, on the VSP side, initially I created an MLT on both of the VSPs and put each interface connecting to the 5520 in the MLT (though I'll admit this doesn't seem right because there's a single interface on each 7432 in an MLT). What happens with this is that the ISIS adjacency continually flaps when both interfaces are up on the 5520, shutting one of them down stabilizes the adjacency, but obviously only to the switch with the active link. I tried switching the MLT to an SMLT on the 5520, but then you can't enable ISIS on an SMLT. 

I can post a diagram and configurations, but I figured to start with this because I'm probably doing something that's clearly wrong and I'm hoping I was descriptive enough. Has anyone found in how to configure redundant fabric uplinks like this in any of the admin guides? 

Thanks!

[TQU · Accepted solution]

Hi cemcjk,

Let the fabric handle the topology !

First, draw your network diagram as you want it, don't care about loop, clusters or full mesh issue you can match which SMLT etc.

Then, check if you have more than one link between to device. If you found some, you need a MLT on them and ISIS need to be configured on the MLT. For all other interfaces, isis will create an adjacency with the remote node. That all ! ISIS will handle the topology.

If you want to priorise links to another, define the spbm l1-metric on both side of link.

About the adjacence flapping on your setup. One ISIS interface for one adjacency ! MLT is one ISIS interface. Both VSP7400 are trying to form adjacency with 5520, on the same ISIS interface. It can't work.

You have to delete the MLT and configure two ISIS interface on each port membre. No MLT is needed here.

regards,

TQU

[EXTR_Paul]

SMLT isn't supported in SPBm because SPBm doesn't support multipoint to Multipoint. 

in this scenario you would just use single link SPBm NNIs between the 5520 and the vist VSP core.

You wouldn't configure any MLT on the 5520 and no SMLT/MLT on the 7400s.   The SPBM NNI's make the MLT/SMLT configuration redundant because SPBm is already topology aware.

If you had a 5520 with a 4 port VIM and two VSP7400-48Ys and you wanted to send two 5520 links to VSP7K One and two links to VSP7k Two, you would just create two MLT groups on each switch. But you wouldn't need to enable it for SMLT on the core.  And it won't let you even if you tried.