host-identifier and option 82

[Michal Vančo]

Hi,

I probably found a solution for this. This works for Cisco CMTS. If you need to force all unicast RENEW request to go through relay agent (to force CMTS to insert option 82), just set server-id to giaddr. This way, all unicast request will go to relay agent and it will deal with them the same way as with broadcasted requests. Just testing this on my CMTS.

regards
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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