Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

enter image description here


In this scenario there is point -to point serial connection between R6 and R7 , there is router R10 whose interface F0/0 is having ip address of and there is a host machine (R9) with ip address which is running an application, My problem is that Application on R9 will only work when it will get its Gateway as which is of router (R10) , is there any way i can make R6 and R7 transparent for R9 and R10, Or any type of routing using GRE / Route-map or any other way.

Thanks in advace

share|improve this question
Admittedly I don't work with routing equipment very often and it's been a very long time since I've done anything like this but I think that using Integrated Routing and Bridging (IRB) might do the trick here. – joeqwerty Nov 11 '12 at 16:51

There's nothing fancy required here - set up bridge-groups on each router that include f0 and s0 and allow the routers to bridge traffic across the point-to-point link. This link is absolutely ancient but the commands haven't really changed and it will get you started.

share|improve this answer
hi I had created BVI and configure IRB on both point to point router but i am able to ping R9 to R10 , Can you help me in this. – user1389735 Nov 12 '12 at 11:41
Hi Rnxrx , i tried it but not able to route the packet form one network to another network . – user1389735 Nov 12 '12 at 13:48
Post the relevant parts of your configuration. The models of the router in question might also be helpful. – rnxrx Nov 13 '12 at 22:53
Thanks in advance Rnxrx , We have cisco 1841 router , and remaining configuration will going to post soon . – user1389735 Nov 14 '12 at 7:56
thanks Rmxrx , yes it is working , now i want make serial as sub interface and use bridge group and BVi is it possible to use it subinterface . – user1389735 Nov 15 '12 at 5:59

Double-NAT is another option. My first thought was GRE which was already mentioned. R9 treats the network on R10's side as a different network and vice versa. R6 source NATs anything from 10.1.1/24 to, say, 10.1.100/24. R7 source NATs anything from 1.1.2/24 to 10.1.200/24.

To access the app on the R9 from R10's network, you'll go to The return traffic from R9 heads back to 10.1.200. R6 and R7 NAT addresses back to the original ones when going back into their respective networks.

No need to add any routes on R9 (host) if default gateway leads back to R6. The only changes are on R6 and R7 for NAT. Imagine if R6 and R7 were firewalls with the PTP link between them as the Internet. Neither side talks directly to the other side's private addresses. Each side talks to the public addresses of the other. In my example, someone sniffing traffic on the PTP link (if they could) would see a conversation between and 10.1.200.x.

share|improve this answer
but in NAT i think I will not able to add route on the server R9 that and cant make as gateway .. – user1389735 Nov 14 '12 at 13:26

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.