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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Indicates the Key Present bit. The rule says Router B needs to drop the packets rather than sending them back the direction from which they came. This field contains the number of encapsulations of GRE packets. Key 32 bits Indicates the Key field. Unsourced material may be challenged and removed. Contains the version number. The Sequence Number field contains an unsigned 32 bit integer which is inserted by the encapsulator.
Generic Routing Encapsulation GRE is a tunneling protocol developed by Cisco Systems that can encapsulate a wide variety of network layer protocols inside virtual point-to-point links or point-to-multipoint links over an Internet Protocol network.
RFC | CCIE or Null!
K 1 bit Indicates the Key Present bit. Feb 25, Such as allowing multicast traffic to traverse the tunnel providing us scalability with the use of a routing protocol.
If this bit is set to 1, then it indicates that the Sequence Number 284 is present. It is used by the receiver to authenticate the received packet. Configuration Request 0x01 Identifier: Contains the checksum of the GRE header and the payload. Indicates the Sequence Number Present bit.
Protocol Type 16 bits Contains the type of the passenger protocol. It is recommended that this bit only be set to 1 if all of the Routing Information consists of Strict Source Routes.
Cisco’s documentation seems to demostrate that they use this exact behavior to make a keepalive work. ICMP 1 Header checksum: The tunnel source can be a physical interface or an IP address just keep in mind the tunnel bre needs to be local on the router.
Generic Routing Encapsulation
It may be used by the receiver to establish the order in which packets have been transmitted from the encapsulator to the receiver. False] [Frame is ignored: Router B could have a route to 1.
Based on the principles of protocol layering in OSI, protocol encapsulation, not specifically GRE, breaks the layering order. However, there are a few things that can be a little rough to get the hang of at first.
If the rule didn’t exist, the packets would just bounce back and forth until the TTL expired. Recur 3 bits Indicates the Recursion Control field.
Then, the IP protocol is responsible for forwarding the packet. 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. Each SRE has the form: My journey to CCIE! Does this imply that an infinite loop is possible or just that the packet will get possibly sent back one time?
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Indicates the Key field.