How to get 192.168.3.2 to successfully ping 192.168.2.3

Question

With the layout described below, the following is true:

• either router can ping any host on either subnet
• 192.168.2.0/25 hosts can ping (and ssh to) 192.168.3.0/24 hosts

but

• 192.168.3.0/24 hosts cannot ping hosts on 192.168.2.0/25

What'd I do wrong?

---

I have the following layout:

Linux Router ip route:

192.168.2.0/25 dev bond0  proto kernel  scope link  src 192.168.2.1 
a.b.c.d/24 dev eth0  proto kernel  scope link  src a.b.c.e  ### Internet upstream
192.168.3.0/24 via 192.168.2.63 dev bond0 
169.254.0.0/16 dev eth0  scope link 
default via a.b.c.d dev eth0 

Cisco Router show ip route:

router-2600#show ip route

     192.168.2.0/25 is subnetted, 1 subnets
C       192.168.2.0 is directly connected, FastEthernet0/0
C    192.168.3.0/24 is directly connected, FastEthernet1/0
S*   0.0.0.0/0 [1/0] via 192.168.2.1

(An iptables firewall is configured on the Linux router but the failure continues whether the firewall is active or not)

Solution

Routing occurs at layer 3. When a host on the 192.168.2.0/25 network pings a host on the 192.168.3.0/24 network it should send the traffic to 192.168.2.1 (assuming that all hosts on the 192.168.2.0/25 network have 192.168.2.1 configured as their Default Gateway and that they don't have a specific route in their routing table for the 192.168.3.0/24 network via 192.168.2.63). 192.168.2.1 then should issue an ICMP redirect (since it has a specific route to 192.168.3.0 via 192.168.2.63) which then sends that traffic to 192.168.2.63. 192.168.2.63 then sends the traffic to the appropriate host on 192.168.3.0/24 (after ARPing for the host). The host on 192.168.3.0/24 then responds to the traffic by sending the response to it's Default Gateway (which is 192.168.3.1) and the traffic travels back to the 192.168.2.0/25 network. If the hosts on the 192.168.3.0/24 network weren't configured with the correct DG and if the Cisco router wasn't configured correctly then the return traffic to the ping initiated by the 192.168.2.0/25 host would never make it back, which leaves me stumped as to why it doesn't work for pings initiated by the 192.168.3.0/24 hosts. The Default Gateway on the Cisco router shouldn't come into play since it's directly connected to both networks and therefore knows how to route traffic to and from both networks.

What do you have set for the DG on the 192.168.3.0/24 hosts? What about the 192.168.2.0/25 hosts?

Can you post the routing table from one of the hosts on each network?

What do you get if you run a trace route from a 192.168.3.0/24 host to a 192.168.2.0/25 host?

How about the reverse?

Comments

[NickW]

who is 192.168.2.63?

[Lorin S.]

.63 is the Cisco Router's f0/0 interface

[NickW]

2.0/24 is directly connected to both? Which of the two boxes is the default gateway?

[Lorin S.]

The 192.168.2.1 is

[Lorin S.]

The physical layout is not set in stone either.. I am attempting to segment a portion of traffic and am laying out the hardware how I believe it should be. Comments and feedback on layout are greatly welcomed.

[NickW]

If the linux box is the GW for the 2.0 network, the cisco needs to know that and route through it accordingly. For the moment, traffic can come from either the cisco or the linux box from the 3.0 network, but will then be sent back through the linux box. This isn't a good idea, and will quite probably cause problems. How you resolve this is up to you, but you need to make one of the two into the default that the other uses to access the network.

[Lorin S.]

I've noticed long delays accessing the 192.168.3.0 hosts. This is probably due to what you described.

[Lorin S.]

So I am attempting to do what you suggested by putting the following default route on the Cisco router: ip route 0.0.0.0 0.0.0.0 192.168.2.1 .... How should I accurately describe the 192.168.2.1 default gateway there?

[NickW]

The problem is primarily that both the cisco and the linux box are in the 2.0/25 network. Unfortunately, the proxy I'm behind won't allow me to see your network diagram, so I can't see what you intend these networks to do. 1 solution might be to set up a 192.168.4.0/29 between the cisco and the linux network, then the cisco would control 3.0/24 traffic, the linux one would control 2.0/25. The cisco could be 192.168.4.1, the linux box 192.4.2, the linux box would have a route 19.168.3.0/24 via 192.168.4.1, the cisco 192.168.2.0/25 via 192.168.4.2 and 0.0.0.0 via 192.168.4.2. HTH