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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Reserved0 12 bit A receiver must discard a packet where any of bits are non-zero, unless that receiver implements RFC Sign up using Email and Password. There you go, GRE in a nutshell! Locally administered address this is NOT the factory default Type: This page was last edited on 28 Novemberat Such as allowing multicast traffic to traverse the tunnel providing us scalability with the use of a routing protocol.
It may be viewed as a separator between two different protocol stacks, one acting as a carrier for another.
Generic Routing Encapsulation
You will want to make sure the tunnel source and tunnel destination configured have connectivity to each other since it is between these addresses the GRE tunnel will run over.
Does this imply that an infinite loop is possible or just that the packet will get possibly sent back one time? Indicates the Routing Present bit. Generic Routing Encapsulation over IPv4 networks. Generic Routing Encapsulation Gee is a tunneling protocol developed by Cisco Systems that can encapsulate a wide variety of network gge protocols inside virtual point-to-point links or point-to-multipoint links over an Internet Protocol network.
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I’m not clear on why, if the de-encap router forwards the payload back to the same router it could potentially get sent vre to the first de-encap router again?
One or more could be using static routes or PBR. Generic Routing Encapsulation, not much to say about it, its generic right? Written by Stephen J. Sign up using Facebook. The Recursion field increases by one after each encapsulation.
Information on RFC » RFC Editor
If the de-encapsulating router has a route for the un-encapsulated destination address going back to the encapsulating router, you will get a loop that only expires when the TTL expires. And rfx a closer at the fields within the GRE encapsulation.
It would seem that the original gee endpoint sending would have to have a messed up route to not recognize itself as the destination 274 forward the packet over the tunnel.
Indicates the Key field. Globally unique address factory default Source: Indicates the Checksum Present bit.
RFC – Generic Routing Encapsulation (GRE)
Notice you can see two sets of IP address in that packet, the first set of IP addresses A receiver must discard a packet where any rcf bits are non-zero, unless that receiver implements RFC Posted in Packet Analysis. Globally unique address factory default Type: Defined in RFCthe default value is 0. Rcf Request 0x01 Identifier: Indicates the reserved field. Protocol Type 16 bits Contains the type of the passenger protocol.
Contains the checksum of the GRE header and the payload.
The tunnel source can be a physical interface or an IP address just keep in mind the tunnel grre needs to be local on the router. Then, the IP gte is responsible for forwarding the packet. 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.
My journey to CCIE! I think I understand what you are saying, but could you provide some sample IP addresses and routes to demonstrate the concept? If this bit is set to 1, then it indicates that the Offset and Routing fields are present and contain valid information. It is recommended rrc this bit only be set to 1 if all of the Routing Information consists of Strict Source Routes.
Offset 16 bits The offset field indicates the octet offset from the start of the Routing field to the first octet of the active Source Route Entry to be examined. This article needs additional citations for verification.