Canonical URL: ; File formats: Plain Text PDF; Status: PROPOSED STANDARD; Updated by: RFC ; Authors: D. Generic Routing Encapsulation (GRE) is a tunneling protocol developed by Cisco Systems that can encapsulate a wide variety of network layer protocols inside. If the de-encapsulating router has a route for the un-encapsulated destination address going back to the encapsulating router, you will get a.

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You will want to make sure the tunnel source and tunnel destination configured have connectivity to each other since it is between these addresses grd GRE tunnel will run over. Then, the IP protocol is responsible for forwarding the packet.

RFC | CCIE or Null!

Defined in RFCno anomaly occurs when rf values of the Recursion field on the sender and receiver are different. If this bit is set to 1, then the Checksum field is present in the GRE header; if this is set to 0, then the GRE header does not contain the Checksum field.

These bits must be sent as zero and must be ignored on receipt. Please help improve this article by adding citations to reliable sources.


Globally unique address factory default Source: Retrieved from ” https: I’m not clear on why, if the de-encap router forwards the payload back to the same router it could potentially get sent back to the first de-encap router again? Cisco’s documentation gree to demostrate that they use this exact behavior to make a keepalive work.

This field is used to prevent the packet from being encapsulated all the time. Views Read Edit View rfd. This article needs additional citations for verification.

Sequence Number 32 bits The Sequence Number field contains an unsigned 32 bit integer which is inserted by the encapsulator. Unsourced material may be challenged and removed.

In this case, the packet MUST be discarded. Protocol Type 16 bits Contains the type of yre passenger protocol. Reserved0 12 bit A receiver must discard a packet where any of bits are non-zero, unless that receiver implements RFC This field contains the number of encapsulations of GRE packets.

Offset 16 bits The offset field indicates the grd offset from the start of the Routing field to the first octet of the active Source Route Entry to be examined. By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.


GRE 47 Header checksum: Occhiogrosso February 6, at 7: Contains the type of the passenger protocol. Feb 25, Indicates the Recursion Control field.

Configuration Request 0x01 Identifier: Care should be taken when forwarding such a packet, since if the destination address of the payload packet is the encapsulator of the packet i. The Recursion field increases by one after each encapsulation.

Generic Routing Encapsulation

False] [Protocols in frame: Post as a guest Name. Each SRE has the form: It is recommended that this bit only be set to 1 if rvc of the Routing Information consists of Strict Source Routes. Currently, it must be set to 0. Indicates the Routing Present bit.

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