host-identifier and option 82

[Michal Vančo]

This exact behavior you will get with Cisco CMTS (my case). Only broadcasted DHCP packets are relayed by CMTS (because cable helper-address is only interested in broadcasted UDP packets). All other DHCP packets go straight to server without any CMTS intervention (no DHCP snooping - no opt 82 insertion).

What I'm trying to figure out now is, whether it will work the way I described in my previous post (i.e. client will try (unsuccessfully) to renew its IP address from T1 to T2 and then, after T2 passes, will issue a broadcast DHCPREQUEST with properly inserted opt 82 and finally rebinds its IP address.

michal

On 27.1.2012, at 13:30, Simon Hobson wrote:

> Michal Vanão wrote:
> 
>> The only problem I've seen so far is that the client fails to renew its IP after T1 passes (because RENEWING DHCPREQUEST is sent directly to server bypassing agent relay). If I understand the RFC correctly, client should "succeed" in REBIND (after T2 passes) because REBINDING DHCPREQUEST is broadcasted hence seen by relay agent. Relay agent shall add opt 82 into DHCPREQUEST in this stage. With properly inserted opt 82, server should be able to match static host decl again.
>> 
>> Is this the way it is supposed to work?
> 
> I suspect it's one of those "grey areas" ! If a relay agent only adds Option 82 to packets it picks up through "normal" operation, then what you've observed is correct.
> 
> While it's not something I've used myself, from comments on this list I get the impression that some equipment will snoop traffic and still add Option 82 to non-broadcast DHCP packets. That does of course require that the relay agent is in the same path as the normal unicast packets - ie a unicast DHCP packet will pass through the same interface, and thus get the same Option 82 value as it would if broadcast.
> 
> -- 
> Simon Hobson
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