dhcrelay is setting the relay ip address wrong

Ihsan Dogan ihsan at dogan.ch
Thu Sep 8 13:36:34 PDT 2005


On Wednesday, 07 Sep 2005 16:27 +0200, Ihsan Dogan wrote:

> > The relay agent is acting exactly the way it should.  When it gets a
> > DHCP request in from a client, it uses its own address ON THE CLIENT'S
> > NETWORK for the relay agent address.  This way, the DHCP server can
> > tell which network the client is on, and thus which set of addresses
> > to use for assigning an address to the client.  
> > 
> > What is the problem?  
> 
> Perhaps I've sent this e-mail too early. I did some further
> investigation and saw that:
> select(7,{4 5 6},{},{},0x0)                      = 2 (0x2)
> gettimeofday({1126033610 52754},0x0)             = 0 (0x0)
> read(0x6,0x806e000,0x1000)                       = 360 (0x168)
> sendto(0x4,0xbfbfd950,0,0x0,{ AF_INET 213.144.141.146:67 },0x10) = 300 (0x12c)
> write(2,0x8066cc0,62)                            = 62 (0x3e)
> write(2,0x80620b8,1)                             = 1 (0x1)
> recvfrom(0x4,0xbfbfe3a0,0,0x0,{ AF_INET 0.0.0.0:68 },0xbfbfe38c) = 300 (0x12c)
> select(7,{4 5 6},{},{},0x0)                      = 1 (0x1)
> gettimeofday({1126033610 72933},0x0)             = 0 (0x0)
> recvfrom(0x4,0xbfbfe3a0,0,0x0,{ AF_INET 213.144.141.146:67 },0xbfbfe38c) = 300 (0x12c)
> 
> The dhcrelay is forwarding the request from the client correctly
> to the server, but it does not forward the reply from the server
> to the client.

I've asked also on the ISC's dhcp server list and this is the
answer I've got:
----------------------------------------------------------------
No, input from this socket is dropped.

See 'fallback_discard' in common/socket.c.


You're railing against a very commonly reported problem.  The IO system
was designed for the server and client (mostly for the server).  It is
poorly suited to the relay.

Enhancements are on the wishlist for 3.1.
----------------------------------------------------------------



Ihsan...

-- 
ihsan at dogan.ch          http://ihsan.dogan.ch/


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