Unable to establishing link between two routers with different subnet

[kasulasaiganesh]

I have two ISR 4351 routers and I'm trying to  esatliblising connectivity between 2 routers with serial interface. Is it possible to connect with different subnets?

R1# serial 0/0/0 

ip address 192.168.1.1/24

encapsulation ppp

R2# serial 0/0/0

ip address 192.168.2.1/24

encapsulation ppp

[Joseph W. Doherty]

It should work with a default routes.

In lieu of the static route statements you have on R1 and R2, have you tried something like:

ip route 0.0.0.0 0.0.0.0 serial0/0/0

on each R1 and R2?

[kasulasaiganesh]

Yes! I tried default route also

# ip route 0.0.0.0 0.0.0.0 serial0/0/0  on both routers.

[Joseph W. Doherty]

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@kasulasaiganesh wrote:

Yes! I tried default route also

# ip route 0.0.0.0 0.0.0.0 serial0/0/0  on both routers.

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And it didn't work?

Curious.  Besides @DaviRocK! noting it worked for him, I just setup a similar environment in PT (attached).

Of course, PT results are not always accurate, but it worked just fine (one PC could ping the other) using just one static route on each router, a static default route.

I've used the subnets/IPs and PPP as you showed in your most recent reply with its exhibited topology.  (Didn't add the additional switches, as not needed for the routing across the topology test.)

You might want to examine the attachment, and compare to what you've been trying.  The attachment's config, is much "simpler" then using FR DLCIs, etc.

BTW, what I've done is what I had in mind for my earlier reply, but perhaps I should have provided a more elaborate explanation.

[DaviRocK!]

Yes, you can establish connectivity between two ISR 4351 routers with serial interfaces using different subnets. To do this, each router needs to be configured with an IP address that is part of a different subnet.

• Assign IP Addresses to Interfaces: Configure the serial interfaces on each router with IP addresses that belong to different subnets. For example, you could use 192.168.1.1/24 for the serial interface of Router 1 and 192.168.2.1/24 for the serial interface of Router 2.

• Configure Routing: Ensure that each router has a route to the other's subnet. This can be done using static routes or a dynamic routing protocol.

Assume the following setup:

• Router 1 has a serial interface labeled Serial0/0/0 with IP address 192.168.1.1/24.
• Router 2 has a serial interface labeled Serial0/0/0 with IP address 192.168.2.1/24.

Here's a basic configuration for each router:

! Configure the hostname
hostname Router1

! Enable the serial interface and assign an IP address
interface Serial0/0/0
ip address 192.168.1.1 255.255.255.0
no shutdown

! Configure a static route to the subnet on Router 2
ip route 192.168.2.0 255.255.255.0 Serial0/0/0

! Configure the hostname
hostname Router2

! Enable the serial interface and assign an IP address
interface Serial0/0/0
ip address 192.168.2.1 255.255.255.0
no shutdown

! Configure a static route to the subnet on Router 1
ip route 192.168.1.0 255.255.255.0 Serial0/0/0

Notes:

• Replace Serial0/0/0 with the correct interface labels for your routers.
• The no shutdown command is used to enable the interface.
• Static routes are used here for simplicity. They tell each router how to reach the subnet connected to the other router.
• This configuration assumes direct connectivity between the two routers via their serial interfaces.

Ensure you're in privileged EXEC mode (enable mode) to enter these configurations and use the configure terminal command to enter global configuration mode on each router. After configuring, you can verify connectivity with the ping command from one router to the IP address of the other router's serial interface.

Best regards

[Joseph W. Doherty]

A variation of what I was alluding to using default routes, but OP never provided actual static routes they were using.

Have you, @DaviRocK! , actually test this?

[DaviRocK!]

Hi Joseph, yes i've test this on 4331

[Joseph W. Doherty]

Great!

Would it be possible for you to replace the far side subnet with a static route like:

Ip route 0.0.0.0 0.0.0.0 serial#

[DaviRocK!]

Sure!

[Joseph W. Doherty]

Thank you.