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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The Routing field is optional and is present only if the Routing Present bit is set to 1.

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Retrieved from ” https: Locally administered address this is NOT the factory default Source: If the rule didn’t exist, the packets would just bounce back and forth until the TTL expired.

It would seem that the original tunnel endpoint sending would have to have a messed up route to not recognize itself as the destination and forward the packet over the tunnel. Indicates the Routing Present bit.

Locally administered address this is NOT the factory default Type: Retrieved May 14, Sign fre using Email and Password.

Generic Routing Encapsulation – Wikipedia

Then, the IP protocol is responsible for forwarding the packet. Router B could have a route to 1. Such as allowing multicast traffic to traverse the tunnel providing us scalability with the use of a routing protocol.

You will want to make sure the tunnel source and tunnel destination configured have connectivity to each other since it is between these addresses 27884 GRE tunnel will run over. Email Required, but never rcc. GRE 47 Header checksum: Reserved1 16 bits The Reserved1 field is reserved for future use, and if present, must be transmitted as zero. Defined in RFCthe default value is 0. R 1 bit Indicates the Routing Present bit.


Generic Routing Encapsulation

ICMP 1 Header checksum: If the number of encapsulations is greater than 3, the packet is discarded. Please help improve this article by adding citations to reliable sources. Ver 3 bits Contains the version number. The Recursion field increases by one after each encapsulation.

Indicates the Checksum Present bit. Sequence Number 32 bits The Sequence Number field contains an unsigned 32 bit integer which is inserted by the encapsulator. Pages using RFC magic links Articles needing additional references from October All articles needing additional references. Bits are reserved for future use. Generic Routing Encapsulation GRE is a tunneling protocol developed by Cisco Systems that can encapsulate a wide variety of network layer protocols inside virtual point-to-point links or point-to-multipoint links over an Internet Protocol network.

These bits must be sent as zero and must be ignored on receipt. 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.

RFC | CCIE or Null!

However, there are a few things that can be a little rough to get the hang of at first. False] [Frame is ignored: This must be set to 0. Sign up gree Facebook.


By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Configuration Request 0x01 Identifier: GRE 0 Protocol Type: It may be used by the receiver to establish the order in which packets have been transmitted from the encapsulator to the receiver.

There is nothing to say that the two routers are running a routing protocol between them, so they could have entirely different ideas of which way to send a packet. This page was last edited on 28 Novemberat This article needs additional citations for verification.

Occhiogrosso February 6, at 7: Contains the version number. This field is present if the Routing Present or the Checksum Present bit is set to 1, and contains valid information only if the Routing Present bit is set to 1.

Protocol Type 16 bits Contains the type of the passenger protocol. Indicates the reserved field. This is an entirely plausible scenario if the rule is not followed. If this bit is set to 1, then it indicates that the Offset and Routing fields are present and contain valid information. Globally unique address factory default Source: 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?

There you go, GRE in a nutshell!