dhcrelay

dhcrelay

[Dr. Lars Hanke]

Hi,

google told me that dhcrelay has been discussed quite a couple of times on 
this list. However,I could not find a solution to my problem.

I want to set up a router, which distributes the DHCP configuration service to 
all subnets attached (well currently only one subnet at eth0, 172.16.2.1). 
Reading the dhcrelay man page
#> dhcrelay -i eth0 adept.mgr

should do exactly that. In practice - almost:

dhcrelay gets the request, asks the dhcp server, gets a reply, but never sends 
it to the requesting device:

#> tcpdump -i any port bootpc or port bootps
09:42:09.996479 172.16.1.12.bootpc > 255.255.255.255.bootps: xid:0x960f0000 
flags:0x8000 [|bootp] 
09:42:09.997009 surtur.mgr.bootps > adept.mgr.bootps: (request) xid:0x960f0000 
flags:0x8000 G:172.16.2.1 ether 0:9:5b:68:19:fb [|bootp] (DF) 
09:42:09.997603 adept.mgr.bootps > 172.16.2.1.bootps: (reply) xid:0x960f0000 
flags:0x8000 Y:ymir.mgr S:adept.mgr G:172.16.2.1 ether 0:9:5b:68:19:fb [|
bootp] (DF) 

... but something like the following never appears (line taken from DHCP 
exchange from server installed on router, alternatively):

09:59:38.780364 172.16.2.1.bootps > 255.255.255.255.bootpc: xid:0x960f0000 
flags:0x8000 Y:ymir.mgr S:172.16.2.1 [|bootp] [tos 0x10] 

Therefore, ymir never gets his IP! 

netfilter policies were set to ACCEPT and all tables were flushed (including 
nat and mangle). I can ping all NIC from anywhere, ymir of course only if it 
is configured!

The system is Debian Woody with 2.4.26-grsec Kernel from backports. grsec 
stuff is not activated by gradm.

Any help appreciated,
 - lars.

Re: [OT] dhcrelay

[Jason Opperisano]

On Tue, Feb 15, 2005 at 09:58:27PM +0100, Dr. Lars Hanke wrote:
> Hi,
> 
> google told me that dhcrelay has been discussed quite a couple of times on 
> this list. However,I could not find a solution to my problem.
> 
> I want to set up a router, which distributes the DHCP configuration service to 
> all subnets attached (well currently only one subnet at eth0, 172.16.2.1). 
> Reading the dhcrelay man page
> #> dhcrelay -i eth0 adept.mgr

from man 8 dhcrelay:

       The -i flag can be used to specify the network interfaces on which
       the relay agent should listen.   In general, it must listen  not
       only  on those  network  interfaces  to which clients are attached,
       but also on those network interfaces to which  the  server  (or
       the  router that reaches  the  server)  is attached.

you only specified one interface--i'm guessing the one that the client
is on.  try using simply:

  dhcrelay adept.mgr

unless you have a reason to exclude some interfaces.

also--what does this have to do with netfilter?

-j

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