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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Locally administered address this is NOT the factory rcf Source: Retrieved May 14, Generic Routing Encapsulation over IPv4 networks. Then, the IP protocol is responsible for forwarding the packet.

Contains the version number. K 1 bit Indicates the Key Present bit. False] [Protocols in frame: The Reserved1 field is present only when the Checksum field is present that is, Checksum Present bit is set to one. GRE 47 Header checksum: Email Required, but never shown.

Ver 3 bits Contains the version number.

From Wikipedia, the free encyclopedia. False] [Frame is ignored: The rule says Router B needs to drop the packets rather than sending them back the direction from which they came.

Post was not sent – check your email addresses! Reserved1 16 bits The Reserved1 field is reserved for future use, and if present, must be transmitted as zero. Feb 25, The Sequence Number field contains an unsigned 32 bit integer which is inserted by the encapsulator. Sign up or log in Sign hre using Google.

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Indicates the Routing Present bit. A receiver must discard a packet where any of bits are non-zero, unless that receiver implements RFC It would seem that the original tunnel endpoint sending would have to have a messed up route gde not recognize itself as the destination and forward the packet over the tunnel.

Offset 16 278 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.

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Indicates the Key field. There is nothing to say that the two routing tables are in sync. Protocol Type 16 bits Contains the type of the passenger protocol.

If this bit is set to 1, then it indicates that the Sequence Number field is present. Indicates the Checksum Present bit. 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.

Currently, it must be set to 0. R 1 bit Indicates the Routing Present bit. Written by Stephen J. Such as allowing multicast traffic to traverse the tunnel providing us scalability with the use of a routing protocol.


Generic Routing Encapsulation

Bits are reserved for future use. GRE 0 Protocol Type: Pages using RFC magic links Articles needing additional references from October All articles needing additional references.

Defined in RFCthe default value is 0. 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. Retrieved from ” https: If router B does send them back, Router A is supposed to discard them, too, based on the rule.

RFC | CCIE or Null!

If the rule didn’t exist, the packets would just bounce back and forth until the TTL expired. This must be set to 0.

And for a closer at the fields within the GRE encapsulation. Contains the checksum of the GRE ggre and the payload. Indicates the Key Present bit.