DISCOVER at wrong port

[Glenn Satchell]

Ok, so what you should see on the server is:

% netstat -an | grep 67
       *.67                                Idle

This means the server is listening on port 67. The dhclient should be 
listening on port 68 for replies. The client may or may not use port 68 
as the source port. Likewise the server may or may nor use port 67 as 
the source port.

The relay is kind of special, it needs to listen on port 68 for 
broadcast messages from clients. dhcp server send packets to the relay 
using unicast (as opposed to broadcast). It then re-transmits those 
packets to the client using a broadcast. The unicast communications 
follows normal conventions - the relay transmits from a random port 
 >1023 with destination port 67. The responses should come back as 
source port 67 and destination the random high port on the relay.

Are you seeing something different to this? Your description doesn't 
help work out what is wrong, so can you post dhcp logs and packet dumps 
using tcpdump? Should only need to see a couple to packets. dhcpd.conf 
and the command line used to start the relay would also be helpful.

regards,
-glenn

On 06/08/11 20:10, neeraj jain wrote:
> Hi Glenn,
>
> Thank you so much for the reply. I have checked the configuration on the
> /etc/services and it is same as you have given.
>
> My problem is that DHCP server is always replying on the 67 port which
> against the protocol. I am not able to find a clue why this is happening?
>
> Please help.
>
> Thanks in advance.
> Neeraj Jain
>
> --- On *Tue, 7/6/11, Glenn Satchell /<glenn.satchell at uniq.com.au>/* wrote:
>
>
>     From: Glenn Satchell <glenn.satchell at uniq.com.au>
>     Subject: Re: DISCOVER at wrong port
>     To: "Users of ISC DHCP" <dhcp-users at lists.isc.org>
>     Date: Tuesday, 7 June, 2011, 5:23 PM
>
>     On 06/07/11 21:39, neeraj jain wrote:
>      > Hi all,
>      > I am facing problem while giving offer to the discovery request. I am
>      > seeing that my relay agent is sending the disocver request at prot 68
>      > and Dhcp server is sending offer at 67 port.
>      > Because of that relay agent is not forwording the response to the
>     client
>      > machine. I am not sure if I can change any thing in the DHCP server
>      > side. Or it is relay agent issue???
>      > Please assis.
>      > Thanks in advance,
>      > Neeraj Jain
>      >
>
>
>     Those port numbers are quite normal, see the entries from
>     /etc/services. Don't get confused by source and destination ports...
>
>     $ grep bootp /etc/services
>     bootps 67/udp # BOOTP/DHCP server
>     bootpc 68/udp # BOOTP/DHCP client
>
>     There must be something else wrong. What messages are in the dhcp
>     server logs?
>
>     -- regards,
>     -glenn
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>