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TAO
Occasional Contributor
Posts: 18
Registered: ‎11-23-2011
Accepted Solution

Is changing the linkcost on a trunked ISL disruptive?

Hi,

 

I'm going to increase the costs of the trunked ISLs on my edge switches:

 

  1. Does changing the cost using the linkcost command disrupt the ISL?
  2. Do I change this just on the edge switch ISL ports, or on the core switch ISL ports where the edge switch ISL connects in to, or both?

Thanks

Valued Contributor
Posts: 531
Registered: ‎03-20-2011

Re: Is changing the linkcost on a trunked ISL disruptive?

1. No. Even if you're setting very high cost to effectively disable the ISL, the packets that are already in flight over this ISL will get to the destination.
2. It's a "duplex" setting. If you have a link between A and B, the cost from A to B which is set on A, could be different than the cost from B to A which is set on B.
TAO
Occasional Contributor
Posts: 18
Registered: ‎11-23-2011

Re: Is changing the linkcost on a trunked ISL disruptive?

Thanks Alexey.

Re point 1, so if I have a 4 port trunked ISL, the ISL will stay functional even if for a moment the ISL ports are configured with different link costs?

Valued Contributor
Posts: 531
Registered: ‎03-20-2011

Re: Is changing the linkcost on a trunked ISL disruptive?

FYI: the cost of trunked ISL is based on the cost set to the trunk master. You will need to set the same cost on all the trunk members though, but that will only matter if the trunk master will get changed over time due to some link reset events etc...

TAO
Occasional Contributor
Posts: 18
Registered: ‎11-23-2011

Re: Is changing the linkcost on a trunked ISL disruptive?

Thanks very much Alexey, appreciate you taking the time to respond.

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