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New Member

GRE Tunnel?

Could someone explain this concept to me?

What other types are there? And how do you configure a GRE Tunnel?


Re: GRE Tunnel?


the tunnel can be configured like this (minimal config):

interface Tunnel1

ip address

tunnel source

tunnel destination

! tunnel mode gre

! this is default and thus not really needed

The idea is to encapsulate traffic (IP and non-IP) into an IP header and to transport it to the tunnel destination, where the gre header will be removed.

This is f.e. useful, when you want to send non-IP traffic across the internet with IPSec encryption.

IPSec could not handle non-IP traffic, but with GRE, you create an IP header and thus IPSec can handle it.

Hope this helps! Please rate all posts.

Regards, Martin

New Member

Re: GRE Tunnel?

Much appreciate the response.

One quick clearification: The section:

tunnel source xx.xx.

tunnel destination xx.xx.

So if I were setting this GRE Tunnel on a router on Site A going to Site B, would the source be the IP address of the WAN interface of Router A, and the destination being the WAN interface IP of Router B?

Hall of Fame Super Silver

Re: GRE Tunnel?

The answer is that it can work correctly configured in different ways. In many cases the source and destination addresses are the WAN interfaces of the routers. But in the case where there might be two WAN interfaces it is prefereble to configure the source and destination addresses as loopback interfaces.

The GRE tunnel can work with source and destination address as WAN, as Loopback, or even as LAN. The only real requirement is that the tunnel destination address must be reachable without going through the tunnel to get to the destination.



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