ip helper-address behavior

If I have multiple DHCP servers, and in turn, multiple ip helper- address lines in my router, how does the router handle this? Does it round robin the requests between the two entries?

Reply to
Terry D
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It sends it to all servers. When we studied our network, we noticed that routers convert DHCP request to unicast, and sends to all configured DHCP servers. So, you cannot control which server will accept and give IP address.

Good luck,

Mike

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Reply to
headsetadapter.com

Interesting. What's best practice? So, both servers could respond with an ip address but the client only accepts one? Isn't this wasteful?

Reply to
Terry D

Hi,

the IP "refused" by the client is not wasted; actually only one IP in the pool is used.

For High-Availability of DHCP serve I suggest you to use a cluster or the classical 80/20 config.

Regards, Gabriele

"Terry D" ha scritto nel messaggio news: snipped-for-privacy@h3g2000cwc.googlegroups.com...

Reply to
Gabriele Beltrame

It's handled by the protocol: client broadcasts request, servers make offers, client broadcasts acceptance of one of the offers (it's broadcast so other servers know they've been declined), accepted server ACKs (or NAKs and the whole thing starts again). So only one address is used per client.

If you're using dynamic pools then you have to make sure your servers' pools don't overlap or that they have a way of synchronising their pools (rare). With statically assigned addresses it doesn't matter - multiple servers are just for redundancy.

Sam

Reply to
Sam Wilson

You can also purchase a DHCP system that offers redundancy without having to use multiple pools. Many of the IP address management systems offer this capability.

Scott

Reply to
Thrill5

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