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GRE, importance of IP address for tunnel interface

Hi All,

Setup is as follows

Net1 Router Our glob network Router Net2

40.40.40.0/24 |Router1| 10.203.118.0/24 |Router2| 40.40.41.0/24

I was trying to establish a tunnel between Net1 to Net2 In Router2(Cisco) I need to give totally 3 addresses Tunnel src=10.203.118.181 Tunnel.dst=10.203.118.182 and tunnel.IP=40.40.41.12/24 If I give the tunnel Ip mentioned it gives error saying it overlaps with the interface connected to Net2 network, obviously it overlaps, but how to get out of this error? what IP I need to configure? What sense it makes when we have already tunnel source and destination addresses(because GRE needs only those two addresses)?

Earlier reply would really help.

Thanks and Regards, Prasanna.

Reply to
Prasanna
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A tunnel /creates/ a new interface and it needs an address. You also need to specify the tunnel soure and destination addresses so that the tunnel (GRE) traffic can flow.

You can typically use /any/ addresses for the tunnel interfaces themselves as long as there is no conflict with existing addresses in your net.

Router1# interface Tunnel200 ip address 192.168.3.133 255.255.255.252 tunnel source FastEthernet0/0 tunnel destination 7.24.241.226

interface FastEthernet0/0 description Internet Facing Link ip address 8.50.7.34 255.255.255.224

Router2# interface Tunnel2 ip address 192.168.3.134 255.255.255.252 tunnel source BVI1 tunnel destination 8.50.7.34

interface BVI1 description Internet Facing Link ip address 7.24.241.226 255.255.255.0

I find this quite confusing, draw pictures.

Reply to
Bod43

Thanks Bod,

I have found the answer in other way

Router1(Proprietary): interface Tunnel1 Source:10.203.118.181 destination: 10.203.118.182 Route entry:

40.40.41.0/24 tunnel1

Interface1 ethernet ip address 40.40.40.1 255.255.255.0

Interface2 ip address 10.203.118.181 255.255.255.0

Router2(cisco)# interface Tunnel1 ip address 40.40.40.12 255.255.255.0 tunnel source FastEthernet0/0 tunnel destination 10.203.118.181

interface FastEthernet0/0 description Internet Facing Link ip address 10.203.118.182 255.255.255.0

interface FastEthernet0/1 ip address 40.40.41.1 255.255.255.0

In Cisco whatever the address we configure that subnet packets are directed to that tunnel. Eg. If we configure tunnel ip address as

40.40.40.13 255.255.255.0 then route entry 40.40.40.0 255.255.255.0 tunnel1, will be created in the routing table dynamically. Thats why it was not allowing to assign IP address falling in any subnet of the existing interfaces. After configuring IP address which falls in destination network, it started working.

Regards, Prasanna.

Reply to
Prasanna

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