DHCPD , dhcp relays on a large network

[Simon Hobson]

Alexandru Coseru wrote:

>The ideea is that   each switch has a subnet  attached to it..
>
>On the backbone   , I have the dhcpd server..
>
>The dhcpd server is not directly attached to the subnets , it has to go
>through a layer3 route to reach them..
>
>
>                  10.1.1.0/24                                 192.168.1.0/24
>srv1     ----------------     L3 SW  A     ------------------------- 
>subnet1

So far it's looking like a normal routed network.

>The L3 SW A  has  DHCPD relay options enabled  ,  so the DHCPD requests
>arrives   on  srv1.
>But srv1  has no knowledge  of  class 192.168.1.0/24  , and the server
>cannot be started  (Error:   No subnet declaration for 192.168.1.0/24).
>The server has only one ethernet NIC , with ip 10.1.1.1  on it..

This doesn't sound right, the server will NOT fail to start because a 
remote subnet is not defined - all that would happen is you would get 
runtime errors in response to requests for unknown subnets.

>Can you elaborate more on shared networks ?

It's a common source of confusion, but I don't think you have one. A 
shared subnet is where you have two different IP subnets on the same 
network segment (or if you are being pedantic on the same broadcast 
domain). In Linux for example, you can add additional IP addresses to 
an ethernet port, eg :

eth0 - a.b.c.d/27
eth0:0 - 192.168.0.1/24
eth0:1 - 172.16.0.0/12

In this topology, a device attached to this ethernet network could 
have an address in any one or more of the three subnets. This is 
indicated to dhcpd via the shared network construct as described in 
the man pages.


Coming back to your problem, can you post the results of 'ifconfig' 
and the contents of your dhcpd.con file ?

Simon