Re: DHCP / BOOTP problems when geting IP from ISP (Telia)

  • From: "Jim Harrison" <jim@xxxxxxxxxxxx>
  • To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
  • Date: Mon, 1 Apr 2002 20:23:57 -0800

For those reading in the wings, DHCP works like this:
The client and the server normally send and receive DHCP messages in the
following order:

** new lease (all broadcast traffic) **
Client  ( Discover ) --> Server
Server ( Offer      ) --> Client
Client  ( Request  ) --> Server
Server ( Ack       ) --> Client
** client has a new IP! **

** lease renewal (normal IP traffic) **
Client  ( Request  ) --> Server
Server ( Ack       ) --> Client
** client has the same IP! **

What typically happens (in the few traces I've been sent, anyway) is that
the client tries to renew its IP with a DHCP "Request", but is answered by a
DHCP "Nak" from the server, causing it to start the lease process from
scratch.
Since ISA doesn't allow broadcast traffic at the external (RED, North)
interface, the DHCP Offer is never seen by the ISA's DHCP client service and
the lease attempt fails.

..just a theory, you understand...

Jim Harrison
MCP(NT4, W2K), A+, Network+, PCG
http://isaserver.org/authors/harrison/
Read the books!
----- Original Message -----
From: "David" <david_agner@xxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Monday, April 01, 2002 9:17 AM
Subject: [isalist] Re: DHCP / BOOTP problems when geting IP from ISP (Telia)


http://www.ISAserver.org


DHCP works if I connect the "RED" interface to my local DHCP server and
the filters are ok. I had this problem earlyer when using a Linux FW "
floppyFW" any one familyar wiht this problem ?

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