UPDATED: Serving addresses to multiple subnets

[John Tabasz (jtabasz)]

I'm sorry I neglected to include many important points in my query. More details here:

 

The DHCP server is ISC 2.0.3 running on Solaris 2.8 on a Sun V120. The DHCP server has a single live interface on the subnet 10.1.100.0/24. 

The router interface to which this subnet is connected is part of a 8 port switch module installed in a Cisco 3725 and has a secondary subnet defined as such:

 

interface Vlan1

 

 ip address 10.1.200.2 255.255.252.0 secondary

 ip address 10.1.100.2 255.255.252.0

 ip helper-address 10.1.100.23 ß------ This is the ip address of the dhcp server.

 standby ip 10.1.100.1

 standby ip 10.1.200.1 secondary

 standby priority 240

 standby preempt

 standby track FastEthernet0/0

 

My dhcpd.conf file (/etc/dhcpd.conf) looks like this:

 

subnet 10.1.200.0 netmask 255.255.254.0 {

option routers 10.1.200.1;

  option subnet-mask 255.255.254.0;

  option domain-name-servers 192.168.199.23,192.168.201.23;

  option domain-name "mydomain.com";

deny unknown-clients;

}

 

subnet 10.1.100.0 netmask 255.255.252.0 {

option routers 10.1.100.1;

  option subnet-mask 255.255.252.0;

  option domain-name-servers 192.168.199.23,192.168.201.23;

  option domain-name "mydomain.com";

deny unknown-clients;

}

 

host fsr7.mydomain.com                   {

   hardware ethernet              0:3:ba:1f:be:f1;

   fixed-address                    10.1.200.38;

   option host-name                "fsr7";

  }

 

host gsr7a.mydomain.com                   {

   hardware ethernet              0:3:ba:3a:73:c4;

   fixed-address                    10.1.100.131;

   option host-name                 "gsr7a";

  }

 

The symptom is that hosts on the 10.1.100.0/22 subnet, which is the primary subnet on the router interface, are getting IP addresses while the hosts on the 10.1.200.0/23 subnet are not. 

Snoop run from the DHCP server tells me that the DHCP request packets are hitting the server. Snoop run on the server looking for outbound packets destined for the MAC address of the host not getting addresses shows no outbound traffic to that address. 

 

I have tried configuring the router interface with the helper address of the DHCP server with no change in results. 

 

Is there some configuration change that needs to be made to tell the DHCP server to reply to requests from a subnet that it is not directly connected to? I have subnet declarations in my config file for both subnets. 

 

Thanks,

 

John

 

 

From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of John Tabasz (jtabasz)
Sent: Wednesday, October 07, 2009 1:49 PM
To: Users of ISC DHCP
Subject: Serving addresses to multiple subnets

 

Hi,

 

I have a Cisco router with a secondary interface on one of the physical interfaces, e.g. 

 

Int fa0

   Ip address 10.1.100.0 netmask 255.255.255.0

   Ip address 10.1.200.0 netmask 255.255.255.0 secondary

 

My dhcp server is sending addresses to the primary subnet, but not to the secondary subnet.

There are subnet declarations for both subnets:

 

subnet 10.1.100.0 netmask 255.255.252.0 {

option routers 10.1.100.1;

  option subnet-mask 255.255.252.0;

  option domain-name-servers x.x.x.x;

  option domain-name "mydomain.com";

deny unknown-clients;

} 

 

 

subnet 10.1.200.0 netmask 255.255.254.0 {

option routers 10.1.200.1;

  option subnet-mask 255.255.254.0;

  option domain-name-servers x.x.x.x;

  option domain-name "mydomain.com";

deny unknown-clients;

}

 

And fixed address declarations for each of the hosts I want to serve addresses to. 

I can see the requests hitting the interface on my dhcp server via snoop, but no response is forthcoming. 

 

Any ideas?

 

Thanks,

 

John

 

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