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Author Topic: What Happens when the ports on the IST go down  (Read 1989 times)

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Offline millendr

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What Happens when the ports on the IST go down
« on: April 18, 2015, 05:45:50 AM »
I was wondering what would happen if all the ports on the IST went down.  I understand that would cause all the SMLTs to go down.  I was wondering what would the end users experience?  Would everything be down or as long as everything was dual attached would everything work normally.

Offline Telair

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Re: What Happens when the ports on the IST go down
« Reply #1 on: April 20, 2015, 12:26:14 PM »
An IST link failure should not happen since you should be running at least 3 IST links between chassis in your core.  But for sake of argument, if the IST's all went down you get what's called a split-brain scenario where the two parts of the cluster are running, but no longer talking to each other.  Neither side knows who's doing what, who's routing, the ARP and routing tables fall out of sync.  General chaos.  Most of the time this leads to your user complaining the network is down.  Dual attached doesn't help as both links have to go to the core to get anywhere and the core is what's not working any more.