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Two Cisco Routers in one class-c network

Hello,

i have two cisco routers, which are connected to one switch. On this switch, there are several servers connected as well.

When i connected the second cisco router, i got messages on the first router, that there is an ip address conflict. After a few minutes it seems as if the vpn tunnel on the first router breaks down because of this conflict. I'm not sure about this, but when i disconnected the second router again, the vpn tunnel could be established again. The vpn tunnel goes to another router via WAN and ends in the local class-c network, where both routers are in.

Router1

LAN 192.168.105.254 (255.255.255.0)

WAN 212.xxx.xxx.xxx

||

||

\/

Cisco Switch

/\

||

||

Router2

LAN IP 192.168.105.253 (255.255.255.0)

WAN IP 217.xxx.xxx.xxx

Router1

int fa 0/1

ip address 192.168.105.254 255.255.255.0

Router2

int fa 0/1

ip address 192.168.105.253 255.255.255.0

Could the /24 mask on the interfaces cause the conflicts?

From the servers, none has the ip 192.168.105.253 or 192.168.105.254 and if i disconnect Router2, the IP 192.168.105.253 is not reachable from any system on the switch.

So how does this ip address conflict occur?

5 REPLIES

Re: Two Cisco Routers in one class-c network

Hi Friend,

You can very well have same subnet on 2 different routers so it is not a problem.

Can you confirm if on remote end where VPN tunnel is terminating if any system has an ip 192.168.105.253 255.255.255.0.

Regards,

Ankur

New Member

Re: Two Cisco Routers in one class-c network

Hello Ankur,

thanks for your answer.

On the remote ends of the vpn tunnels are no local networks with 192.168.105.0/24.

I changed the ip of the second router to 192.168.105.252 ... 251 and 250, all unused so far. But the error messages still occured.

This evening i will try again.

Regards,

chasm

New Member

Re: Two Cisco Routers in one class-c network

hello,

can you check the router 1 log. with error message you should have a mac address

May 10 05:32:20.489: %IP-4-DUPADDR: Duplicate address 10.10.10.1 on GigabitEthernet0/1.1, sourced by 0003.oc12.a2c3

This should help you to identify host already with 192.168.105.253.

Before connecting Router 2, from Router 1 ping 192.168.105.253 and do a sh arp ?

HTH,

regards,

cisand

New Member

Re: Two Cisco Routers in one class-c network

Hello Cisand,

i will do this this evening. Tomorrow i will post the logging messages and the sh arp result.

Thanks for your answer

chasm

New Member

Re: Two Cisco Routers in one class-c network

This time, no duplicate ip error messages occured.

I dont know what was the issue last time.

But this time i got another problem, but i will do a new conversation for it, because it is not related to the issue of this conversation.

Thanks for your help

chasm

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