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Community Member

Is duplicate ip addresses possible?

Hello

I have 2 routers. Looking at the first one I have a Cisco 2500 with E0/0 ip 10.240.240.16 and s0/0 10.0.30.66 When I ask it where I am routing 196.37.102.101 & .102 it shows me these 2 are routed to 10.0.30.66. SO I telnet to this 10.0.30.66 and am asked for a password. So far so good.

After having logged in by typing in the password I discover I am on a new router. Interfaces: E0 10.30.17.1 & S0 10.0.30.66. This router is a Cisco 2600! And there are no 2 users. It shows there's only 1 user on it. Then I ask this router where does it route the 2 196 addresses as mentioned above and it shows me they are routed to the E0 interface.

Looking at the configs on both routers they have plain vanilla configs. A few ACL's and route statements and nothing more. The scariest part is the 2 ip addresses are accessible from the LAN in front of the first router (Cisco 2500).

Yet there are no ip conflicts on the LAN. None captured in the log files on the routers. So how is this possible? What am I missing?

2 REPLIES
Hall of Fame Super Bronze

Re: Is duplicate ip addresses possible?

The LAN won't report IP conflict since these devices' IP it's on the WAN side.

They won't know about each other, unless you advertise each of their serial interfaces via static or dynamic routing *and* even then - you won't see any ip conflict reported in the LAN.

It would be up to the dynamic or static routing implemented sourcing from the LAN as to which device you will connect when requesting services from/to 10.0.30.66

Community Member

Re: Is duplicate ip addresses possible?

I think in IPv6 we can have two hosts have the same IPv6 address.it serves like a multicast feature. you send a packet to that IP and both of them receives it.

Srinath.M

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