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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 the GRE tunnel will run over. Unsourced material may be hre and removed.

The Reserved1 field is present only when the Checksum field is present that is, Checksum Present bit is set to one. Not set Fragment offset: A receiver must discard a packet where any of rc are non-zero, unless that receiver implements RFC There is nothing to say that the two routing tables are in sync. Reserved1 16 bits The Reserved1 field is reserved for future use, grw if present, must be transmitted as zero.

K 1 bit Indicates the Key Present bit. Please help improve this article by adding citations to reliable sources.


RFC – Generic Routing Encapsulation (GRE)

Locally administered address this is NOT the factory default Source: The tunnel destination is going to the address of the remote router you are terminating the tunnel to. It is recommended that this bit only be set to 1 if all of the Routing Information consists of Strict Source Routes. 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.

Sequence Number 32 bits The Sequence Number field contains an unsigned 32 bit integer which is inserted by the encapsulator.

Such as allowing multicast traffic to traverse the tunnel providing us scalability with the use of a routing protocol. The Reserved1 rfcc is reserved for future use, and if present, must be transmitted as zero. Post as a guest Name.

Generic Routing Encapsulation

However, there are a few things that can be a little rough to get the hang of at first. Then, the IP protocol is responsible for forwarding the packet.

Key 32 bits Indicates the Key field. ICMP 1 Header checksum: The first thing unlike physical interface you can declare tunnel interfaces from configuration mode and you can start at any number.


There is nothing to say that the two routers are running a routing protocol between fre, so they could have entirely different ideas gte which way to send a packet. Bits are reserved for future use. Flags 5 bits Indicates the reserved field. Generic Routing Encapsulation, not much to say about it, its generic right?

There you go, GRE in a nutshell! False] [Protocols in frame: The rule says Router B needs to drop the packets rather than sending them back the direction from which they came.

Generic Routing Encapsulation – Wikipedia

Indicates the Key field. Protocol Type 16 bits Contains the type of the passenger protocol. Thanks for the answer.

Indicates the Recursion Control field. Home Questions Tags Users Unanswered. Indicates the Checksum Present bit.

The tunnel source can be a physical interface or an IP address just keep in mind the tunnel source needs to be local on the router. Reserved0 12 bit A receiver must discard a packet where any of bits are non-zero, unless that receiver implements RFC