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Forum Replies

  1. That would be a good idea. I’ll write something soon.

  2. Dear Rene,

    1. Can you please tell why did you used:

    tunnel source fastEthernet 0/0

    and not:

    tunnel source 192.168.12.1

    instead? What would be the difference ?

    1. Now, this might sound silly but anyway … Given the below config:
    HQ(config)#interface tunnel 1
    HQ(config-if)#tunnel source fastEthernet 0/0
    HQ(config-if)#tunnel destination 192.168.23.3
    HQ(config-if)#ip address 192.168.13.1 255.255.255.0
    

    what I still cannot understand (I have read a couple of articles on GRE) and seems very strange to me is how the ip address of the tunnel is 192.168.13.1 and the source

    ... Continue reading in our forum

  3. Hi Adrian,

    When you use the tunnel source command, you can define an interface or an IP address. When you use the interface, the router will check for the IP address on the interface and use that so the end result is the same.

    The tunnel source and destination addresses are only used to build the tunnel, that’s it. When you use this to tunnel something over the Internet, we typically use the public IP address on the outside interfaces for this.

    You can use loopbacks as the source addresses if you want redundancy. Let’s say we have two routers that are connected

    ... Continue reading in our forum

  4. Hi Adrian,

    Once the GRE tunnel is up, it acts like a regular interface. With normal interfaces we also don’t see the next hop IP address within the IP packet.

    Here’s the logic of the router:

    1. When HQ sends a packet with destination 172.16.3.3 it has to check its routing table for a match:
    HQ#show ip route eigrp 
    
          172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
    D        172.16.3.0/24 [90/27008000] via 192.168.13.3, 00:00:07, Tunnel1
    
    1. Above you can see that the next hop is the remote IP address of the tunnel. Now it has to do another lookup to fig
    ... Continue reading in our forum

  5. Hi Vitaly,

    The loopbacks won’t affect your neighbor adjacency whatsoever. The neighbor adjacency is established on the tunnel interface so any other interfaces don’t have any effect on it. It won’t matter if you use a /24 or /32 on the loopback interfaces :slight_smile:

    Do you still have your config with the /24s on the loopback that is not working?

    Rene

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