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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Does this imply that an infinite loop is possible or just that the packet will get possibly sent back one time?

Generic Routing Encapsulation

Locally administered address this is NOT the factory default Source: Please help improve this article by adding citations to reliable sources. Indicates the Routing Present grw. Currently, it must be set to 0. Post Your Answer Discard 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.

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RFC – Generic Routing Encapsulation (GRE)

If router B does send them back, Router A is supposed to discard them, too, based on the rule. It may be used by the receiver to establish the order in which packets have been transmitted from the encapsulator to the receiver. This is an entirely plausible scenario if the rule is not followed. Notice you can see two sets of IP address in that packet, the first set of IP addresses Not set Fragment offset: Protocol Type 16 bits Contains the type of the passenger protocol.


Post was not sent – check your email addresses! 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. The rule says Router B needs to drop the packets rather than sending them back the direction from which they came.

The Reserved1 field is present only when the Checksum field is present that is, Checksum Present grw is set to one. Occhiogrosso February 6, at 7: 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.

From Wikipedia, the free encyclopedia. Generic Routing Encapsulation over IPv4 networks.

One or more could be using static routes or PBR. Views Read Edit View history.

Such as allowing multicast traffic to traverse the tunnel providing us scalability with the use of a routing protocol. GRE 47 Header checksum: If this bit is set to 1, then it indicates that vre Sequence Number field is present. There you go, GRE in a nutshell! Globally unique address factory default Source: The Recursion field increases by one after each encapsulation.


Retrieved from ” https: If this bit is set to 1, then it indicates that the Offset and Routing fields are present and contain valid information. If the rule didn’t rtc, the packets would just bounce back and forth until the TTL expired.

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However, there are a few things that can be a little rough to get the hang of at first. Indicates the Key Present bit.

Reserved0 12 bit A receiver must discard a packet where any of bits are non-zero, unless that receiver implements RFC False] [Frame is ignored: Each SRE has the form: K 1 bit Indicates the Key Present bit.