Configuring static routes at the network edge

[eshah]

We have some Cisco 1750 routers at the edge of our network which are running RIP. We were advised to use static routes on the router, since there was only one route (across a WAN link) for traffic to go from the hub connected to the router, as RIP would only waste the limited bandwidth to the router. We posted this problem previously and got a response which stated :You could set up a default static route on your edge router, run RIP on your internal routers in order to propagate the default, but block the RIP to the outside.

On your edge router, make a default route to your external link. Keep RIP running as before, but add the line redistribute static in your rip configuration. That will get the default route propagated.

Now to stop the RIP on the external interface: If the link is on a different major IP network to your internal network, you can simply not include it in the network commands under rip. But if it is in the same network, then RIP will be enabled on the interface, so you will have to add passive-interface xxxxx, where xxxxx refers to the interface carrying your external link,

Alternatively, you could define your default route using the ip default-network command. This will get propagated automatically into the RIP even without the redistribute command.

We tried it, the problem is that the router is unreachable, via the serial or Ethernet, although if connected to the router via console port, with the configuration screen , you are able to ping external locations, and are able to telnet into the router, but he PC's on the Ethernet side of the router cant see the network.

Assistance\Advice requested.

attached you wll find , the actual reply , and a copy of some info from our work file.

[Georg Pauwen]

Hello,

can you post the configuration of your edge and of your hub router ?

Regards,

GP

[eshah]

Yes , I can post the configuration and i will do so as soon as possible, I made one mistake we are able to connect to the router via the serial port , but not the ethernet port.

[Richard Burts]

I have read the file with your original question and the response from Kevin. I have also read the file with the comments on what you have attempted but I am not sure that I fully understand the situation. Could you supply some information to clarify: I assume that Salvage is the remote 1750 and the connected router is Passport? Could you give information about what is the connected LAN(s) on Salvage and the addresses of the serial interfaces.

I also find it a little confusing what changes were made on which machine. As I understand it what should have happened is that the remote router at the edge of the network should have configured a static default route pointing to the central router. The remote edge router should not be running RIP. The central router should have a static route for the subnet(s) of the edge router, should redistribute static into RIP, and should have passive-interface for the WAN interface connecting the central router to the edge router. Is this what was done, or was it done differently?

If you help us understand the environment better we will be more able to find answers to assist you in resolving this.

HTH

Rick

[eshah]

The work Salvage refers to a location, at this location (building) we have a 1750series router.This router is the remote edger router.The 1750 series router at Salvage is connected via its serial port (172.20.2.2) to a Cisco 3640 router (172.20.1.4).

The ip address at the ethernet side of the 1750series Router at Salvage is 172.20.27.1.

So what did as specified by Kevin was:

Changed configuration on 1750 router at Salvage as follows:

1. Set up a default route on the router, using “ ip route 0.0.0.0 0.0.0.0 172.20.1.4

2. Entered the “Redistribute static “ command in the RIP configuration, so that the default route can be propagated

3. Stop the RIP on the external interface: Since the link is on the same IPnetwork as the internal network, then RIP will be enabled on the interface , so the command “ passive-interface xxxxx “ is added to the RIP configuration, where xxxxx refers to the interface carrying the external link, thus in this case the command used was “passive-interface s0” .

On completing these steps, we were able to telnet into the 1750 series router at the salvage, but was unable to communicate with the ethernet interface of the same 1750 series router .

When a pc was connected via its serial port to the console port of the router , using hyperterminal to access the configuration, we were able to ping external locations easily.

Hence the issue really lies with respect to communication via the ethernet port (LAN) of the 1750 series router at the salvage .

Hence , we can communicate via the serial port but not the ethernet port of the 1750series Router at the salvage.

Hope this clears it up somewhat?

I have attached a copy of the configuration of the 1750series router at the salvage.

[Richard Burts]

Ernie

I have looked at the config that you posted and I see several issues. The serial interface on Salvage is 172.20.2.2. Your message indicates that it is connected via serial to a 3640 which your message seems to indicate is 172.20.1.4. But that makes the 3640 on a different subnet. Connections over a serial link should be in the same subnet on both ends. (The exception to that is when you are using the ip unnumbered feature - which you are not). I suspect that part of your problem is that the routers do not see themselves on a connected subnet. When you run RIP over the link it can compensate for that to some degree. But when you stop RIP the problem has impact.

Also I see that you have a static default route as Kevin suggested. And in RIP you have redistribute static. But there is no default metric defined. To redistribute into RIP you need a default metric. Another aspect of the problem with the default route is that the next hop for the default route is 172.20.1.4, but without RIP running I believe that Salvage has no idea how to get to that address. You can confirm this by doing show ip route 172.20.1.4 on Salvage. I suspect that you will get an error about route not in table.

Beyond these issues I believe that there is a larger problem of misunderstanding. When I look at your original post in this thread it talks about not running RIP over the serial link. And when I read Kevin's response the first paragraph is describing not running RIP over the serial interface when it says do static default on your edge router and run RIP on your internal router. If you are not running RIP over the serial interface then I see no reason to run RIP on Salvage at all. There is one piece of this that Kevin did not address. If you do not run RIP over the serial link then how does the 3640 know about the Ethernet subnet at Salvage. I believe that the answer is that the 3640 needs to configure a static route to 172.20.27.0 with the 1750 serial interface as the next hop. And if there are other routers that the 3640 communicates with via RIP then the 3640 needs to redistribute static into RIP (remembering to have a default metric).

If you address these issues I believe that you will have connectivity from the central network to the remote subnet on Salvage.

HTH

Rick

[eshah]

Here is the configuration, hope it helps ?

[amit-singh]

Are you able to ping the Ethernet interface of the salvage router, if you have a PC connected to it ???

What does " show int fa 0" says on your 1750 router. I see that you have passive-interface S0 configured on 1750 so this interface will not participate in sending and receiving of routing updates from another RIP neighbor.

As pointed out by Rick in his last post, its not the configuration that should be on your 1750.

The following configuration changes should be made at 1750.

1.Take the RIP config out of 1750 i.e your edge router.

2. Just have a default route pointing to your 3640 router.

3.Your 3640 i.e central router should run rip and it should have static routes poinintg to the subnets of 1750 and those should be redistributed as static.

4. The serial interface of the 3640 should be configured as passive-interface for RIP.

Once this is done you will be able to achieve the desired results and also the appropriate design.

Please revert in case of any issues.

regards,

-amit singh