Edit an existing PortChannel group to add more ports

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Nov 5th, 2009
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I am planning on increasing the bandwidth on an existing PortChannel group this coming Weekend.

Although, I have done this on a couple of occasions earlier in prior versions of SANOS, but we are at a newer version of SANOS (3.3.2) now and hopefully it remains same procedure.

I will be using the following steps.

1. Verify the new ports identified for PC are shut (down)on both swicthes.

2. Update these new ports to the following on both the switches:

a. Mode Admin as "E"

b. Speed Admin as "4Gb" (these are MDS directors with SANOS)

c. Rate Mode as "Dedicated"

d. Port VSAN as "1"

3. Add these new ports to the existing PortChannel on both the switches.

4. And bring up (no shut) one port at a time.

Please let me know if I am missing anything to make this a non-disruptive upgrade?

Appreciate your feedbacks at the earliest.

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Overall Rating: 5 (1 ratings)
stephen2615 Fri, 11/06/2009 - 01:05
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I generally get the ISL up and running and then add it to the Port Channel. I have the ports up as they need to be seen by each other. The ISL ports probably should be in the VSANs that you have allowed to use the Port Channel. I don't trunk unwanted VSAN traffic across the ISL's/Port Channels.

I would rather have the ISL's functional before I would add anything to the Port Channels. I don't understand why you have the ports turned off in the first place. How do you intend to add the ports to the port channels? I use the Port Channel GUI in Fabric Manager and it works a treat.

I expect that there may be a bit of traffic disruption as there normally is in any change. If there is, it shouldn't be too much and any traffic will be resent anyway. Expect some events anyway.. Thats the reason these changes are made in change windows isn't it?

Michael Brown Fri, 11/06/2009 - 07:16
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Adding links to a port channel is designed to be non-disruptive. Once the new link is added, it is added into the hashing algorithm of available links. Since the MDS uses only 1 link for an entire exchange, there should be no impact to existing traffic when adding, or removing a link from a port channel. As was suggested, I would ensure the link is up as an ISL, then add it to port channel.


pavanksharma Mon, 11/09/2009 - 07:37
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Both of your procedures may be applied if there are two existing ISLs and you want them to be part of a new PortChannel.

I followed my procedure.

My intent is to add more NEW ports to an existing PortChannel and which is also as laid out in the MDSCook 3.1 Book (page 5-9).

Appreciate your feedbacks, though.

metzger_jon Mon, 11/16/2009 - 05:50
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When removing a link from a port channel, doesn't the FSPF cost change requiring an FSPF recalculation for all VSANs which are trunked across the channel?

Michael Brown Fri, 11/20/2009 - 12:37
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Actually, the design of the port channel is such that removing or adding a link will not cause an FSPF recalculation...unless the reduction is more than 50%.  So if you have 3 four gig links...creating a 12 gig port channel, and you losed 1...your bandwidth drops to 8, but the MDS will not recalculate the FSPC link cost.  If you lose 2 of the 3, then it will.

Hope this helps,



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