dhcp relay - stateless

foomail123 foomail123 at yahoo.com
Wed Jul 19 22:40:41 UTC 2006

Thank you for last response.

Since dhcp relay is stateless, if there are multiple
interfaces, how does relay know which interface to
foward DHCP offer received from server ?

How does relay work in vlan case (multiple interfaces
in a vlan) ?

Also, being stateless if same host is connected to
multiple interfaces and/or vlans, how does relay
process DHCP offer packet received from server ?


--- Simon Hobson <dhcp1 at thehobsons.co.uk> wrote:

> foomail123 wrote:
> >1) For DHCP relay - where do I find documentation,
> >how to configure, debug etc. (from developer point
> >of view) ?
> Starting point would be "man dhrelay"
> >2)  Does dhcp relay maintain state of each request/
> >response between server and client ? If so, is
> there
> >tool to dump dhcp relay database ?
> No, DHCP Relay is a stateless function.
> >3) Is relay a independent daemon ? Any dependency
> on
> >server code or runtime ?
> It's a standalone package, it does not even have to
> be run on a 
> routing machine. It also is not dependant on having
> a particular 
> vendors DHCP Server.
> >4) what are steps to run dhcp relay ?
> Check the man page.
>  From memory (of reading this list, I don't use
> dhrelay myself), you 
> would want (where is the dhcp server) :
> dhrelay
> or
> dhrelay -i eth0 -i eth1 1234
> to use only specific interfaces.
> A quirk of the way implementation was done is that
> you must tell the 
> relay to listen not only on the client facing
> interface, but also on 
> the interface that replies from the server will come
> from. If you are 
> running the relay on some machine on the clients
> subnet (not a 
> router) then these are both the same interface, but
> if the machine is 
> also the router they will be different. Also related
> to this quirk is 
> that the connection towards the server cannot be a
> PPP interface.
> Simon

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