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Community Member

Why tunnel key has to be same in DMVPN

Hi Everyone,

need to understand why tunnel key has to be same between all the routers in the DMVPN?

Thanks

MAhesh

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Why tunnel key has to be same in DMVPN

Tunnel key is how one demultiplexes multiple GRE tunnels.

Quoting RFC:

   The Key field contains a four octet number which was inserted by the
   encapsulator. The actual method by which this Key is obtained is
   beyond the scope of the document. The Key field is intended to be
   used for identifying an individual traffic flow within a tunnel. For
   example, packets may need to be routed based on context information
   not present in the encapsulated data.  The Key field provides this
   context and defines a logical traffic flow between encapsulator and
   decapsulator.  Packets belonging to a traffic flow are encapsulated
   using the same Key value and the decapsulating tunnel endpoint
   identifies packets belonging to a traffic flow based on the Key Field
   value.

http://tools.ietf.org/html/rfc2890

2 REPLIES
Cisco Employee

Why tunnel key has to be same in DMVPN

Tunnel key is how one demultiplexes multiple GRE tunnels.

Quoting RFC:

   The Key field contains a four octet number which was inserted by the
   encapsulator. The actual method by which this Key is obtained is
   beyond the scope of the document. The Key field is intended to be
   used for identifying an individual traffic flow within a tunnel. For
   example, packets may need to be routed based on context information
   not present in the encapsulated data.  The Key field provides this
   context and defines a logical traffic flow between encapsulator and
   decapsulator.  Packets belonging to a traffic flow are encapsulated
   using the same Key value and the decapsulating tunnel endpoint
   identifies packets belonging to a traffic flow based on the Key Field
   value.

http://tools.ietf.org/html/rfc2890

Community Member

Why tunnel key has to be same in DMVPN

Hi MArcin,

Many thanks for the useful info

Regards

MAhesh

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