DHCP Relay agent - Duplicating messages
Gero Palacio
gero.palacio at gmail.com
Mon Jun 29 22:12:56 UTC 2015
Hi All,
I found a weird behavior on the DHCP relay agent which is duplicating the
outgoing messages from the client when it's not supposed to.
This is the set up:
[client] <-> (192.168.1.1) [relay_agent] (10.0.0.1) <-> [pair of failover
servers](10.0.1.10 & 10.0.1.11)
*What I found is this:*
*No. Source Destination Info*
-- We're good here. Relay agent duplicate the discovery messages
-- to send to both pair of servers
*44* 10.0.0.1 10.0.1.11 DHCP Discover - Transaction ID
0xd2728f7c
*45* 10.0.0.1 10.0.1.10 DHCP Discover - Transaction ID
0xd2728f7c
-- Receives only 1 response from 1 of the servers. So far, so good.
*47* 10.0.1.10 192.168.1.1 DHCP Offer - Transaction ID
0xd2728f7c
-- This bit is also okay. Client broadcasts the request message
-- relay agent sends 2 messages (one to each server)
-- receives only 1 response (good).
*48* 10.0.0.1 10.0.1.11 DHCP Request - Transaction ID
0xd2728f7c
*49* 10.0.0.1 10.0.1.10 DHCP Request - Transaction ID
0xd2728f7c
*50* 10.0.1.10 192.168.1.1 DHCP ACK - Transaction ID
0xd2728f7c
-- This is the part where it gets weird.
-- Client sends 1 requst (WireShark on the client confirms this, not shown)
-- This message contains:
-- Relay agent IP address: 0.0.0.0 (0.0.0.0)
*52* 192.168.1.60 10.0.1.10 DHCP Request - Transaction ID
0xd2728f7c
-- Relay agent (source 10.0.0.1) makes 4 messages!! I dont get this part
-- These 2 messages contains:
-- Relay agent IP address: 192.168.1.1 (192.168.1.1) ???
*53* 10.0.0.1 10.0.1.11 DHCP Request - Transaction ID
0xd2728f7c
*54* 10.0.0.1 10.0.1.10 DHCP Request - Transaction ID
0xd2728f7c
-- These 2:
-- Relay agent IP address: 10.0.0.1 (10.0.0.1) ???
*55* 10.0.0.1 10.0.1.11 DHCP Request - Transaction ID
0xd2728f7c
*56* 10.0.0.1 10.0.1.10 DHCP Request - Transaction ID
0xd2728f7c
-- The response are received with the client ip and with
-- the relay agent ip that's facing the client
*57* 10.0.1.11 192.168.1.1 DHCP ACK - Transaction ID
0xd2728f7c
*58* 10.0.1.10 192.168.1.60 DHCP ACK - Transaction ID
0xd2728f7c
*59* 10.0.1.10 192.168.1.1 DHCP ACK - Transaction ID
0xd2728f7c
Why is this happening? Why is the DHCP Relay Agent IP is changing in the
DHCP message?
I've read the DHCP Handbook chapters discussing relay agents (Ch 7 and 9)
and also the chapter that describes the ISC relay agent but it doesn't seem
to behave in that way.
I'm using version 4.2.8
Thanks for your help.
Gero.
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