Secure DHCP?

Daniel Senie dts at
Sun Jul 25 02:45:39 UTC 1999

Nicholas Bastin wrote:
> (I felt this message had enough operational relevance to post on this list.  If
> any feels otherwise, please let me know.)
> After having experienced a rather malicious attack on our corporate network by
> someone running a rogue DHCP server, I'm wondering if there's any way to
> prevent this from happening again?

You don't specify whether this was a corporate network or a production
(e.g. cable) network. The short answer (especially if a corporate
network): get him fired, or worse. (I.e. take some sort of legal
action). If a public, network, such as a cable modem system, that'd be
fairly nasty...

>  The perpetrator basically managed to
> renumber most of an entire subnet (into an entirely different IP block) of our
> network, causing a major denail of service.  I've read the RFC's and checked
> all the network reference books I can find, and none of them indicate any way
> to prevent this from happening again.  Am I missing something here, or is it
> time to start writing RFC's?  Thanks in advance.

Well, the problem that comes up, is how does the workstation figure out
who to trust? The DHCP client basically knows nothing about the IP
addressing of the network (which is why it's asking a DHCP server). It's
not desirable to have it know anything, because that'd limit the ability
to have your DHCP client be portable. The best thing about DHCP is the
ability to plug into any LAN anywhere that supports DHCP, and be able to

There may well be some ways to authenticate a legitimate DHCP server
from an illegitimate one, but discussion of that is probably off-topic
for NANOG. I'd be happy to discuss the matter further off this list, or
on an appropriate list, however, and would like to hear more details of
the situation in your case.


Daniel Senie                                        dts at
Amaranth Networks Inc.  

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