Re: DHCP and routing across subnets
- From: "Bill Grant" <not.available@online>
- Date: Thu, 30 Jun 2005 16:10:14 +1000
You cannot fix this problem by changing things in DHCP or on the RRAS
server. The default gateway settings should point to the DSL routers only
(ie the router option in DHCP should be to the DSL router). This gives both
subnets access to the Internet. The gateway setting to the RRAS server does
nothing useful, so remove it.
All traffic (including that for the other local subnet) goes to the
default gateway (the DSL router) by default. What you need to do is add a
static route to each DSL router to redirect the local traffic to the RRAS
router. For the router at 192.168.1.1 , add a static route
192.168.2.0 255.255.255.0 192.168.1.16
And a corresponding route on the other router at 192.168.2.1
192.168.1.0 255.255.255.0 192.168.2.16
If you cannot add routes to the routers, you will need to add the extra
route to each client to get traffic for the "other" local subnet to the
internal router.
Eric Nutt wrote:
> I'm having a devil of a time setting up DHCP to support the following
> configuration using 2 DSL routers and a Windows 2000 Server running
> RRAS.
>
> Internet <-> 68.x.x.x [DSL Router] 192.168.1.1 <Subnet 1> 192.168.1.16
> [DHCP/RRAS Server] 192.168.2.16 <Subnet 2> 192.168.2.1 [DSL Router]
> 65.x.x.x <-> Internet
>
> The DHCP server is configured with 2 scopes, 192.168.1.0 and
> 192.168.2.0 Scope ...1.0 (Subnet 1) has 003 Router option set to
> 192.168.1.1, 192.168.1.16 Scope ...2.0 (Subnet 2) has 003 Router
> option set to 192.168.2.1, 192.168.2.16
>
> The normal options for DNS and WINS are set on both Scopes.
>
> RRAS is set up for LAN routing only with default settings.
>
> What works:
> - The clients on Subnet 1 and Subnet 2 both get the appropriate DHCP
> addresses and settings applicable to their scope.
> - The clients on both subnets are able to route to the internet over
> their respective internet connections (verified using tracert)
> - The clients on both subnets are able to access the services and
> resources on the DHCP/RRAS server
>
> What does not work:
> - The clients on Subnet 1 cannot send/receive traffic to/from Subnet
> 2 and vice versa.
> - Clients on Subnet 1 cannot ping ...2.16 and clients on Subnet 2
> cannot
> ping ...1.16
>
> Resolution steps so far:
> - Checked routing table on RRAS server, routes exist for both subnets
> and their interfaces.
> - Successfully pinged clients on both subnets from the RRAS server.
> - Checked client routing tables ... Subnet 1 clients have no
> pre-defined route for Subnet 2 and vice versa.
> - Added 033 Static Route option for Subnet 2: 192.168.1.16,
> 192.168.2.16, which allowed me to ping the ...1.16 interface from
> clients on Subnet 2. - Modified 033 Static Route option for Subnet 2:
> 192.168.1.16, 192.168.2.16, 192.168.1.0, 192.168.1.16, which allows
> me to continue pinging ...1.16, but does not allow me to ping
> anything else on Subnet 1 (e.g. ...1.1). - Checked the routing table
> for the clients and the subnet mask for the ...1.0 entry is set to
> 255.255.255.255.
>
> I can't seem to find a way to alter the subnet mask in the routing
> table as part of the DHCP options.
>
> Any suggestions on how to resolve this issue?
.
- References:
- DHCP and routing across subnets
- From: Eric Nutt
- DHCP and routing across subnets
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