From: Jelle Borsje (borsjej@yahoo.dk)
Date: Wed Apr 13 2005 - 07:31:34 GMT-3
Hej,
When it comes to the configuration, and usage, it is
almost the same. The encapsulation type on the tunnel
interface is ipinip, instead of gre.
In reality, IPinIP simply puts an IP header in front
of the original packet. The outside IP header, has
protocol type 4 and the source and destination
addresses are the tunnel endpoints. Since there is no
'customized' header, there is no field to indicate a
protocol type, unlike GRE.
The GRE header is an additional header that is placed
between a new (outside IP header) and the payload (the
original packet we want to travel through the tunnel,
which could well be an IP packet). The outside IP
header contains source and destination IP addresses of
the tunnel endpoints. The GRE header contains a number
of fields, interestingly a protocol type field. This
means the payload could be many different types of
protocols, not just IP. This means that we can tunnel
other protocols in GRE tunnels, not only IP. IPinIP
tunnels can only tunnel IP traffic as far as I know.
I think you would have a hard time getting ISIS (since
it uses CLNS) to work over IPinIP encapsulated
tunnels, while it works over GRE. IPX can also be
transported in a GRE tunnel.
When it is just IP traffic you are looking at, the
difference between them is probably not striking...
when you want to run other protocols than IP through
the tunnel, it becomes more appearant.
Hope this helps a little.
Greetz
Jelle
--- stephen skinner <stephenski@gmail.com> wrote:
> hello ,
>
> i was recently doing the NMC self-assessment .and
> there was one topic
> on there that i don`t know and i have tried in vain
> to find out some
> info .
>
> what is the difference between IPinIP and GRE
> tunnels
>
> TIA
>
> Steve
>
>
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