GRE encapsulation

[mnaveen]

Hi,

I just wanted to know the significance of having different IP address for the GRE tunnel source and the GRE tunnel interface IP address ? What will be the source and destination IP addresses of a GRE packet in this case.

All pointers are welcome.

Naveen.

[dnagarajachary]

The tunnel ip address is the ip address u specify as in any other interface. Each interface should have an ip address to communicate.

Now the tunnel source address can be the same as tunnel ip address or it can be different ip address. When you give the tunnel source as the tunnel ip address, then the traffic till or from the tunnel ip address are encapsulated to protect the traffic.

When you give the tunnel source , a different ip address, as is the usual case, for example, the inside local ethernet ip address or ethernet interface itself, the traffic from or till the ethernet interface is protected.

-Deepu

[mnaveen]

Hi Deepu,

Thanks for the reply. But I couldn't get a scenario where in I can use tunnel source address different from that of the tunnel ip address. Do you know one ?

Moreover, any use doing this ? Because anyway the LAN packets will never be protected (the tunnel ends at the LAN interface itself !)

Thanks,

Naveen.

[dnagarajachary]

You can refer this site

http://www.cisco.com/warp/public/707/multiroute.html#intro

where the tunnel source is the fastethernet

By doing this you are ensuring that the packet is protected till the LAN end.

-Deepu