dhcpd sending on the same IP it receives on

Jared Gillis jared at sonic.net
Tue Feb 5 21:09:33 UTC 2008

Jeffrey Hutzelman wrote:
> --On Tuesday, February 05, 2008 11:16:13 AM -0800 Jared Gillis 
> <jared at sonic.net> wrote:
>> Scott Baker wrote:
>>> That seems like a semi-complex setup for just one server. Wouldn't it be
>>> easier to just run two different (physical) servers for that odd corner
>>> case you're running in to?
>> Sure, but this configuration is replicated for nearly 30 routers. 15
>> servers serving 30 routers is far better for datacenter space, power,
>> cooling and just financially than running 30 servers.
> Even better would be to serve all 30 routers from one server (well, two 
> or three, for redundancy).  Unless there is something weird about your 
> network topology, there is no reason the DHCP server needs to be 
> directly connected to the router.
Indeed, and we have considered that, but re-building our entire DHCP infrastructure to fix a relatively minor problem that might be worked around/patched quickly.

> Failing that, you could also configure the DHCP server's routing table 
> such that traffic to each subnet goes to the appropriate router, such 
> that the kernel will select the appropriate source address.
That is another option, but the routers are serving many different subnets, so static route configuration is problematic to manage, running a routing protocol on the server is another option, but obviously not ideal.

> It would be nice if the DHCP server were to respond to unicast requests 
> using the address to which the request was sent, but if I recall 
> correctly that's not quite as trivial a code change as one might hope.

It's sounding like there's no easy fix for this, I'll submit a bug and maybe it'll be resolved in future releases. Proper TCP/IP behavior is something that should be aimed for. =)

> -- Jeffrey T. Hutzelman (N3NHS) <jhutz+ at cmu.edu>
>   Carnegie Mellon University - Pittsburgh, PA

Jared Gillis - jared at corp.sonic.net       Sonic.net, Inc.
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