Same ip address in two different serial link

[kamlesh.sharma]

Hi all

two routers are connected via two serial port R1=====R2

i configured both the serial port s0 and s1 with ip add 192.168.1.1/24 on R1 and ip add 192.168.1.2/24 on R2. It was working and load balancing was also working.

can somebody guess what is happening here really it is load balancing or what though i know that each interface should have different ip address in route

please Help.

Thanks in advance

[Richard Burts]

I think that you have encountered one of the subtlties of the behavior of IOS. IOS is very careful with interface addresses and subinterface on LAN interfaces and will not allow two LAN interfaces to have IP addresses in the same subnet (much less the same IP address on the interfaces). But on serial interfaces it does not do the same checking. I have configured serial interfaces before where both serial interfaces were in the same subnet (I do not remember that I have ever configured the same address on both interfaces). I found that the serial interfaces worked ok with two interfaces in the same logical subnet.

I have never been sure of why the behavior was different. But I have rationalized the difference in terms of the fact that on LAN interfaces where there are multiple other stations, it is necessary to resolve the layer 2 address via ARP (or similar techniques) and duplicate addresses (or two addresses within the same subnet) would break that. But on serial (point to point) there is no ambiguity about who the neighbor is and no need to resolve the layer 2 address, it does not break anything if two interfaces are in the same subnet (or duuplicated addresses).

I believe that it is really load balancing. Whether you are running a dynamic routing protocol or using static routes, on point to point interfaces the next hop is not dependent on resolving the layer 2 address of the neighbor and is dependent on sending out the proper interface. So load balancing would work ok in this circumstance.

HTH

Rick

[kamlesh.sharma]

Thanks a lot for your reply.

Address resolution protocol works on broadcast media where gratitutous arp works to register mac address of host to switch.i was thinking about frame-relay inverse-arp which use to map DLCI to remote ip address so other end of router must be having to same entry in show frame-relay pvc.

Thanks in advance again.