Cisco – Overlapping with Serial0/0/0

ciscointerfaceping

I have tried configuring the serial interfaces and it is working for two devices which is my HQ1 and HQ2:

  • HQ1 – IP address 120.244.121.136 on Serial0/0/0
  • HQ2 – IP address 120.244.121.139 on Serial0/0/0

The above two do ping, however, when I do the bottom two, they are not pinging, and I am getting an error regarding overlaps with serial0/0/0:

  • RM1 – IP address 120.244.121.140 on Serial0/0/0
  • HQ1 – IP address 120.244.121.143 on Serial0/1/1

Each has a subnet mask of 255.255.255.0.

Does anyone have any suggestions?

Best Answer

Your problem is that, on the HQ1 router, you are attempting to put the same network on multiple routed interfaces. I think you mean these serial interfaces to be for point-to-point links. You should use a network (/31 or, if you are more traditional, /30) for your point-to-point links. You would then have two usable addresses for the links, and one of the two addresses goes on one end of the link, and the other address goes on the other end of the link.

Alternatively, you could use any other network size, but you need to use separate networks on the two interfaces in the same router.

Routers route between networks; they don't route from one network to the same network. How will the routing table know to which of the two interfaces in the same network it should forward packets for that network?

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