DHCPINFORM via a relay agent
Kan Sasaki
sasaki at fcc.ad.jp
Mon Aug 21 05:24:19 UTC 2006
From: "David W. Hankins" <David_Hankins at isc.org>
Subject: Re: DHCPINFORM via a relay agent
Date: Sun, 20 Aug 2006 15:47:13 +0000
> This is a compounded bug. Existing code that attempted to work with
> clients that specify a ciaddr of 0.0.0.0 was 'enhanced' to deal even
> better with them. In the meantime, we appear to have brkoen clients
> that specify non-zero ciaddr via relays.
>
> You will have noted from your careful reading of rfc already that
> such zero-ciaddr-DHCPINFORM clients are already not implementing
> rfc2131.
Do you mean that this is zero-ciaddr-client-handling issue?
The following scenario describes my question.
0. basis
Client has an IP Address CCC.CCC.CCC.CCC which has been assigned by
server. Relay agent has two IP Addresses, GGG.GGG.GGG.GGG (client
side) and XXX.XXX.XXX.XXX (server side). Server has an IP Addresses
SSS.SSS.SSS.SSS. Client is MS windows XP. Server and relay agent
are ISC's.
1. Client broadcasts DHCPINFORM.
ip src CCC.CCC.CCC.CCC
ip dst 255.255.255.255
ciaddr CCC.CCC.CCC.CCC
giaddr 0.0.0.0
yiaddr 0.0.0.0
2. Relay agent receives the message and relays the following to the
server.
ip src XXX.XXX.XXX.XXX
ip dst SSS.SSS.SSS.SSS
ciaddr CCC.CCC.CCC.CCC
giaddr GGG.GGG.GGG.GGG
yiaddr 0.0.0.0
3. Server receives the message and replies the following to the relay
agent.
ip src SSS.SSS.SSS.SSS
ip dst GGG.GGG.GGG.GGG
ciaddr CCC.CCC.CCC.CCC
giaddr GGG.GGG.GGG.GGG
yiaddr 0.0.0.0
The ISC dhcpd always replies to giaddr if it has giaddr. I guess
that the server should send the DHCPACK reply to the client
directly.
4. Relay agent receives the reply message and relays to the 0.0.0.0.
ip src GGG.GGG.GGG.GGG
ip dst 0.0.0.0
ciaddr CCC.CCC.CCC.CCC
giaddr GGG.GGG.GGG.GGG
yiaddr 0.0.0.0
The ISC dhcrelay always forwards the reply message to yiaddr if it
has no broadcast flag.
Is it wrong to send the DHCPACK reply to ciaddr instead of giaddr
whether the DHCPINFORM has giaddr?
--
Fusion Communications Corp.
Kan Sasaki sasaki at fcc.ad.jp
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