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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It is recommended that this bit only be set to 1 if all of the Routing Information consists of Strict Source Routes. Posted in Packet Analysis. Defined in RFCno anomaly occurs when the values of the Recursion field on the sender and receiver are different.
The rule says Router B needs to drop the packets rather than sending them back the direction from which they came. Not set Fragment offset: S 1 bit Indicates the Sequence Number Present bit.
Generic Routing Encapsulation
GRE 47 Header checksum: Based on the principles of protocol layering in OSI, protocol encapsulation, not specifically GRE, breaks the layering order. Sign up or log in Sign up using Google.
This page was last edited on 28 Novemberat My journey to CCIE! K 1 bit Indicates the Key Present bit. 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. After receiving a certain network layer protocol such as IPX packet that needs to be encapsulated and routed, the system adds a GRE header to the packet, and then encapsulates the packet into another protocol such as IP.
R 1 bit Indicates the Routing Present bit. It is used by the receiver to authenticate the received packet.
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Such as allowing multicast traffic to traverse the tunnel providing us scalability with the use of a routing protocol. Indicates the Strict Source Route bit. This is an entirely plausible scenario if the rule is not followed. This article needs additional citations for verification.
Indicates the reserved field. These bits must be sent as zero and must be ignored on receipt. Globally unique address factory default Source: It may be viewed as a separator between two different protocol stacks, one acting as a carrier for another.
Written by Stephen J.
RFC | CCIE or Null!
Reserved0 12 bit A receiver must discard a packet where any of bits are non-zero, unless that receiver implements RFC However, there are a few things that can be a little rough to get the hang of at first.
Notice you can see two sets of IP address in that packet, the first set of IP addresses The tunnel destination is going to the address of the remote router you are terminating the tunnel to.
Key 32 bits Indicates the Key field. The Reserved1 field is reserved for future use, and if present, must be transmitted as zero. Views Read Edit View history. If the number of encapsulations is greater than 3, the packet is discarded. Sequence Number 32 bits The Sequence Number field contains an unsigned 32 gte integer which is inserted by the encapsulator.