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Topic: Generic Routing Encapsulation

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	GRE: Generic Routing Encapsulation
		Generic Routing Encapsulation is a protocol for encapsulation of an arbitrary network layer protocol over another arbitrary network layer protocol.
		When a tunnel endpoint decapsulates a GRE packet which has an IPv4 packet as the payload, the destination address in the IPv4 payload packet header must be used to forward the packet and the TTL of the payload packet MUST be decremented.
		GRE is defined by IETF (http://www.ietf.org) in RFC 2784.
	www.networkdictionary.com /protocols/gre.php (350 words)

	RFC 2784 (rfc2784) - Generic Routing Encapsulation (GRE)
		In the most general case, a system has a packet that needs to be encapsulated and delivered to some destination.
		GRE version number 1 is used by PPTP [RFC2637].
		Additional GRE version numbers are assigned by IETF Consensus as defined in RFC 2434 [RFC2434].
	www.faqs.org /rfcs/rfc2784.html (1791 words)

	RFC 2784 (Site not responding. Last check: 2007-10-12)
		RFC 2784 Generic Routing Encapsulation March 2000 In the most general case, a system has a packet that needs to be encapsulated and delivered to some destination.
		Forwarding Decapsulated IPv4 Payload Packets When a tunnel endpoint decapsulates a GRE packet which has an IPv4 packet as the payload, the destination address in the IPv4 payload packet header MUST be used to forward the packet and the TTL of the payload packet MUST be decremented.
		Security Considerations Security in a network using GRE should be relatively similar to security in a normal IPv4 network, as routing using GRE follows the same routing that IPv4 uses natively.
	www.armware.dk /RFC/rfc/rfc2784.html (1817 words)

	Generic Routing Encapsulation on the Cisco CMTS
		Therefore, if you define a specific GRE policy on a device group, both the hub and the spoke must be descendants of that device group and there must be no overriding policy on a lower level that changes the GRE policy on either the peering hub or spoke.
		GRE includes information on what type of packet you are encapsulating and information about the connection between the client and server.
		GRE Tunneling is a protocol for transporting an arbitrary network layer protocol (the payload) over another arbitrary network layer protocol (the delivery).
	www.cisco.com /univercd/cc/td/doc/product/software/ios123/123newft/123limit/123b/ubr_gre.htm (2527 words)

	RFC 4023 - Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE). T. Worster, Y. Rekhter, E. Rosen, Ed.. (Site not responding. Last check: 2007-10-12)
		Encapsulation in GRE The MPLS-in-GRE encapsulation encapsulates an MPLS packet in GRE [RFC2784].
		RFC 4023 Encapsulating MPLS in IP or GRE March 2005 Whether such modifications are made, and the details of how they are made, will depend on the configuration of the tunnel tail and the tunnel head.
		RFC 4023 Encapsulating MPLS in IP or GRE March 2005 so presupposes that there is effective destination-based (or a combination of source-based and destination-based) filtering at the boundaries.
	rfc.sunsite.dk /rfc/rfc4023.html (3877 words)

	[No title]
		The GRE key field is not needed for demultiplexing, as the top MPLS label of the encapsulated packet is used for that purpose.
		The GRE key field is sometimes considered a security feature, functioning as a 32-bit cleartext password, but this is an extremely weak form of security.
		Similarly, at the tunnel tail, the DS field of the encapsulating IPv4 or IPv6 header MAY be used to determine the Behavior Aggregate of the encapsulated MPLS packet.
	www.isi.edu /in-notes/rfc4023.txt (3917 words)

	RFC 1701 (rfc1701) - Generic Routing Encapsulation (GRE)
		In the most general case, a system has a packet that needs to be encapsulated and routed.
		Routing Present (bit 1) If the Routing Present bit is set to 1, then it indicates that the Offset and Routing fields are present and contain valid information.
		The exact algorithms for the generation of the Sequence Number and the semantics of their reception is outside of the scope of this document.
	www.faqs.org /rfcs/rfc1701.html (1590 words)

	QNX Developer Support
		GRE (Generic Routing Encapsulation) or IP tunneling (IP encapsulation) is a technique that encapsulates IP datagrams within IP datagrams.
		GRE is a technique that allows datagrams to be encapsulated into IP packets and then redirected to an intermediate host.
		Outgoing datagrams are encapsulated by an IP header of protocol type 47, and a GRE header specifying the type of the encapsulated datagram (currently only IP).
	www.qnx.com /developers/docs/momentics_nc_docs/neutrino/technotes/gre.html?printable=1 (601 words)

	[No title]
		GRE is already commonly used to tunnel CLNP PDUs over IP and so using GRE to tunnel IP over CLNS gives a common approach to tunnelling and may simplify software within network elements that initiate and terminate tunnels.
		It is suggested that GRE should be transported over CLNS at the lowest layer possible, which is as a transport layer protocol over the network layer.
		The originator of the packet that is inside the GRE packet will not have visibility of the packet loss or the reason for the packet loss, and a fl hole may form.
	www.isi.edu /in-notes/rfc3147.txt (1465 words)

	RFC1701 (Site not responding. Last check: 2007-10-12)
		RFC 1701 Generic Routing Encapsulation (GRE) October 1994 The Routing field is a list of Source Route Entries (SREs).
		RFC 1701 Generic Routing Encapsulation (GRE) October 1994 is set to 1, then the Address Family field should be checked to determine the semantics and use of the SRE Length, SRE Offset and Routing Information fields.
		RFC 1701 Generic Routing Encapsulation (GRE) October 1994 Acknowledgements The authors would like to acknowledge Yakov Rekhter (IBM) and Deborah Estrin (USC) for their advice, encouragement and insightful comments.
	rfc.net /rfc1701.html (1640 words)

	generic from FOLDOC
		Generic programs often embody non-traditional kinds of polymorphism; ordinary programs are obtained from them by suitably instantiating their parameters.
		Different occurrences of a generic type variable in a type expression may be instantiated to different types.
		The universal quantifier "for all a:" means that a is a generic type variable.
	ftp.sunet.se /foldoc/foldoc.cgi?generic (990 words)

	IPSec (IP Security): Part 3 - GRE
		The next header field refers to the encapsulated protocol, while the length field is used to denote the size of the authentication data payload as measured in 4 byte words.
		Generic routing encapsulation is itself a protocol that will encapsulate another network layer protocol and in turn be sent via another network layer protocol.
		This new packet that used GRE to encapsulate the original packet is then itself encapsulated into another protocol and sent on its merry way to the destination IP address.
	www.windowsnetworking.com /articles_tutorials/IPSec-IP-Security-Part3-GRE.html (1485 words)

	Dr. Dobb's \| A Virtualization Technologies Primer, Theory: Part 5 \| November 27, 2006
		GRE provides a method of encapsulating arbitrary packets of one protocol type in packets of another type (the RFC uses the expression X over Y, which is an accurate portrayal of the problem being solved).
		GRE allows private network data to be transported across shared, possibly public infrastructure, usually using point-to-point tunnels.
		Although GRE is a generic X over Y solution, it is mostly used to transport IP over IP (a lightly modified version was used in the Microsoft Point-to-Point Tunneling Protocol [PPTP]; and, recently, we are seeing GRE used to transport MPLS).
	www.ddj.com /dept/64bit/196513339 (595 words)

	RFC 2890 - Key and Sequence Number Extensions to GRE
		Abstract GRE (Generic Routing Encapsulation) specifies a protocol for encapsulation of an arbitrary protocol over another arbitrary network layer protocol.
		Packets belonging to a traffic flow are encapsulated using the same Key value and the decapsulating tunnel endpoint identifies packets belonging to a traffic flow based on the Key Field value.
		If only at certain instances the protocol being carried in the GRE tunnel requires in-sequence delivery, only the corresponding packets encapsulated in a GRE header can be sent with the sequence bit set.
	www.packetizer.com /rfc/rfc.cgi?num=2890 (1832 words)

	Cisco, IBM to enhance cluster load balancing
		The software, called Generic Routing Encapsulation (GRE), is intended to overcome the limitations of Cisco and IBM load balancing techniques for equalizing client requests and server responses among IBM S/390 systems in a Sysplex cluster.
		The Cisco/IBM GRE implementation is based on technology defined in Internet Engineering Task Force RFC 1701 and 1702 documents, which means the software can work in multivendor networks, and is a result of the two vendors' $2 billion networking alliance (See story).
		GRE will alleviate that by enveloping TCP/IP packets for transport through MNLB and OSA Express, and then stripping off that envelope and sending the packet to the proper TCP/IP stack within the Sysplex, he says.
	www.networkworld.com /archive/2000/106572_09-11-2000.html (684 words)

	gre-tun - a GRE tunnel implementation for FreeBSD
		Generic Router Encapsulation (GRE) tunnels are defined by the Internet Engineering Task Force (IETF) in two Requests for Comments (RFCs): RFC1701 Generic Router Encapsulation, and RFC1702 Generic Routing Encapsulation over IPv4 networks.
		GRE is a very simple, low overhead approach - the GRE protocol itself can be expressed in as few as 8 octets.
		This is the address to which GRE encapsulated packets will be sent, so it must be reachable from the local tunnel endpoint.
	mike.spottydogs.org /projects/gre-tun (1582 words)

	GRE - Generic Routing Encapsulation, GRaphics Engine
		Generic Routing Encapsulation is not the only word formed from GRE.
		A tunneling protocol developed by Cisco that can encapsulate a wide variety of protocol packet types inside IP tunnels, creating a virtual point-to-point link to Cisco routers at remote points over an IP internetwork.
		By connecting multiprotocol subnetworks in a single-protocol backbone environment, IP tunneling that uses GRE allows network expansion across a single-protocol backbone environment.
	www.auditmypc.com /acronym/GRE.asp (197 words)

	RFC 1702
		In an earlier memo [RFC 1701], we described GRE, a mechanism for encapsulating arbitrary packets within an arbitrary transport protocol.
		GRE packets which are encapsulated within IP will use IP protocol type 47.
		If the source route is a strict source route and the next autonomous system is NOT an adjacent autonomous system, the packet should be dropped.
	www.apps.ietf.org /rfc/rfc1702.html (808 words)

	Cisco administration 101: Configure GRE tunnels
		GRE is a tunneling protocol used to transport packets from one network through another network.
		Because GRE takes one packet and encapsulates it in another packet, you might run into a situation where the packet you're sending is larger than your interface allows.
		Because GRE tunnels are stateless, it's possible for one side of the tunnel to go down while the other side remains up.
	articles.techrepublic.com.com /5100-1035_11-6141478.html?part=rss&tag=feed&subj=tr (906 words)

	RFC2784
		This specification is generally concerned with the structure of the GRE header, although special consideration is given to some of the issues surrounding IPv4 payloads.
		An RFC 1701 transmitter may set any of the Routing Present, Key Present, Sequence Number Present, and Strict Source Route bits set to one, and thus may transmit the RFC 1701 Key, Sequence Number or Routing fields in the GRE header.
		GRE version number 1 is used by PPTP [RFC 2637].
	www.scit.wlv.ac.uk /rfc/rfc27xx/RFC2784.html (1622 words)

	Generic Routing Encapsulation Tunnel IP Source and Destination VRF Membership - Cisco Systems
		Each VRF table comprises an IP routing table, a derived Cisco Express Forwarding (CEF) table, and guidelines and routing protocol parameters that control the information that is included in the routing table.
		Previously, GRE IP tunnels required the IP tunnel destination to be in the global routing table.
		The default destination is determined by the global routing table.
	cio.cisco.com /en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a00805e1e8e.html (744 words)

	Clavister Firewall Changes from v8.30.01 to v8.40.00
		As of v8.40.00, Clavister Firewall supports GRE tunnels, which is a standardized way of encapsulating, among other things, IP packets inside IP packets.
		In "virtual firewall" scenarios, it may be useful to remove the firewall's own IP addresses from a (policy-based) routing table, so that it does not occupy address space that may be in use elsewhere in the network.
		As of v8.40.00, pings generated by an active cluster member will be sourced from the shared IP address.
	www.clavister.com /releasenotes/changes-8.30.01-to-8.40.00.html (2785 words)

	Roxen Community: RFC 4797 Use of Provider Edge to Provider Edge (PE-PE) Generic Routing Encapsulation (GRE) or IP in ...
		That is, a GRE or IP tunnel replaces the tunnel LSP that was present in "conventional" BGP/MPLS IP VPNs.
		The encapsulation header would have the address of the egress PE router in its destination IP address field, and this would cause the packet to be delivered to the egress PE router.
		The IP destination address field of the encapsulation header will contain the value of the associated BGP Next Hop; this will be an IP address of the egress PE router.
	community.roxen.com /developers/idocs/rfc/rfc4797.html (2044 words)

	[No title]
		Hanks, Li, Farinacci & Traina [Page 4] RFC 1701 Generic Routing Encapsulation (GRE) October 1994 The Routing field is a list of Source Route Entries (SREs).
		If the Routing Present bit Hanks, Li, Farinacci & Traina [Page 5] RFC 1701 Generic Routing Encapsulation (GRE) October 1994 is set to 1, then the Address Family field should be checked to determine the semantics and use of the SRE Length, SRE Offset and Routing Information fields.
		Hanks, Li, Farinacci & Traina [Page 7] RFC 1701 Generic Routing Encapsulation (GRE) October 1994 Acknowledgements The authors would like to acknowledge Yakov Rekhter (IBM) and Deborah Estrin (USC) for their advice, encouragement and insightful comments.
	www.ietf.org /rfc/rfc1701.txt (1677 words)

	[Cisco] Schwachstelle in Cisco IOS Generic Routing Encapsulation (GRE) - cisco-sr-20060906
		Generic Routing Encapsulation (GRE) ist ein von Cisco entwickeltes Netzwerkprotokoll welches dazu dient, andere Protokolle einzukapseln um diese zum Beispiel durch IP-Tunnel zu transportieren.
		CSCuk27655 / CSCea22552 / CSCei62762 - Schwachstelle in Cisco IOS Generic Routing Encapsulation (GRE) In Cisco IOS ist eine Schwachstelle beim Verarbeiten von GRE Paketen mit GRE Source Routing Informationen entdeckt worden.
		Additional Information ====================== Generic Routing Encapsulation (GRE) is a generic packet encapsulation protocol.
	archive.cert.uni-stuttgart.de /win-sec-ssc/2006/09/msg00021.html (694 words)

	GRE, Generic Routing Encapsulation
		Indicates the byte offset from the start of the Routing field to the first byte of the active Source Route Entry to be examined.
		Indicates the byte offset from the start of the Routing Information field to the first byte of the active entry to be examined.
		The GRE header used in PPTP is enhanced slightly from that specified in the current GRE protocol specification.
	www.networksorcery.com /enp/protocol/gre.htm (572 words)

	GRE - Generic Routing Encapsulation
		Generic Routing Encapsulation is an internet based term applied to the encapsulation of IP datagrams tunnelled through the internet.
		The encapsulation includes security, typically in the form of IPSec, and is most commonly found in VPN (Virtual Private Network) implementation.
		RFC (Request For Comment) 1701 and 1702 define these standards.
	www.mpirical.com /companion/IP/GREEncapsulation.htm (50 words)

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