Why do partially failed/failing switches fail to pass DHCP?

Posted by David Mackintosh on Server Fault See other posts from Server Fault or by David Mackintosh
Published on 2010-05-11T21:53:46Z Indexed on 2010/05/11 22:04 UTC
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Filed under:

dhcp

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switches

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ethernet

I've noticed this several times: a switch starts to behave oddly. Usually if the switch doesn't fail outright, what tends to get noticed is that DHCP doesn't work.

We had a Linksys SRW-224P fail today. Systems which were still connected worked properly, until it came time to renew their DHCP lease. Once the lease expired, they stopped working, but up until then we couldn't detect a failure. This includes PoE VoIP phones -- they work fine until their lease is up, at which point they're done.

I've noticed this on the above-mentioned Linksys, three varieties of 3Com, and possibly half a dozen dumb switches.

What is it about DHCP that makes it sensitive to failing switches?

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