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Occasional Contributor
Posts: 5
Registered: ‎05-16-2018

Ring Topology only using one path..?

Hello,

 

we have 2 fabrics, recently configured into a ring network via two DWDM ISP Paths. Check this thread.

 

Both Fabric A and B travel down 2 ISP paths between our DC and Edge office, but currently, data is only travelling down on path, as you can see from the attached BNA fabric topology graphic.

 

I've had a look through the historical logs and that's confirmed. Traffic did travel down the other path for a short period of time - couple of days, but now all travells down the the path you see in blue.

 

We're not maxing out the ISL bandwidth, occassionally we jump into yellow - between 40-80%, but not that often.

 

Is this the expected behavior for a ring topology? Would the alternative path light up if we push too much traffic down the live path?

 

The path that isn't currently used is the original path, so no configuration has changed on the two switches that make up that ISP ISL Trunk.

 

 

Frequent Contributor
Posts: 134
Registered: ‎03-20-2018

Re: Ring Topology only using one path..?

This could be expected behavior. Fabric Shortest Path First (FSPF) could be in play here.

Occasional Contributor
Posts: 5
Registered: ‎05-16-2018

Re: Ring Topology only using one path..?

Thanks for the reply, I did think that, but the active path is 5km longer! Very peculiar.

 

If the ISL on the active path went over say 80%, would you expect the load to be balanced?

 

Should we just stick all Fabric A down one ISP path and Fabric B down the other? With no loop completed?

Frequent Contributor
Posts: 88
Registered: ‎01-19-2018

Re: Ring Topology only using one path..?

FSPF doesn't know anything about the length of the links. All the links have the same cost unless you would manually change some of them.

Frequent Contributor
Posts: 134
Registered: ‎03-20-2018

Re: Ring Topology only using one path..?

I think more clarity is needed.

 

In Fabric A

 

Red group = Ring

Blue group = Star

Black group = Line

 

Black to Red = Line

Black to Blue = Completes a ring

 

Where is your issue? The yellow and blue line connecting Blue and Red? If so, I don't see a ring, unless there is some additional connection to Fabric B.

 

Fabric B is similar, except that Red group is a Star, and Black group is a Star.

Occasional Contributor
Posts: 10
Registered: ‎07-11-2018

Re: Ring Topology only using one path..?

Yes, this is expected behaviour, and no, your other link will not get used if the primary gets clogged. FOS will always prefer a path with 2 hops to a path with 3 hops. You can see which path is used with the command "topologyshow".

Consider connecting switch_10_pvl to the 6510 instead of the 5100.
Regular Contributor
Posts: 209
Registered: ‎04-04-2018

Re: Ring Topology only using one path..?

Hello,

you may play with link cost to make preferred path with 3 hops.

Please mark this response as "Accept as Solution" if it answers your question.

Marian Bezeg

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