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TCP/IP Gateway-to-Gateway Protocol (GGP)
(Page 2 of 2)
Propagation of Routing Table Information
One interesting difference between
GGP and RIP is that in GGP, networks and costs aren't sent in pairs.
Instead, a GGP router sends its routing table in groups. If it has three
networks it can reach at a cost of 1 it sends those in a group with
distance value 1, then if it has a few at a cost of 2 it sends those
in a group with distance value 2, and so on. Another difference is that
GGP Routing Update messages are acknowledged. Each Routing
Update message is sent with a sequence number, which is used to
ensure that out-of-date information is not propagated. If the Routing
Update is received and has a new sequence number (indicating that
it is recent information), the router processing it sends back a GGP
Acknowledgment message back to the originator. If the sequence
number indicates the message is stale, a Negative Acknowledgment
is sent instead and the message discarded.
As a distance-vector algorithm using
hop count as a metric, GGP shared most of the same pros and cons as
RIP. It had simplicity on its side, but had various
problems such as slow convergence and
issues such as the counting to infinity problem. GGP was
a much more rudimentary protocol than RIP, however, and did not include
many of the features
included in RIP to handle such issues,
such as split horizon. GGP was also limited to unsubnetted classful
networks, due to its age.
Current Role in TCP/IP
When Internet architecture moved
to the use of autonomous systems, GGP was obsoleted. While it was an
important part of TCP/IP history, it is today not formally considered
a part of the TCP/IP protocol suite.
Key Concept: The Gateway-to-Gateway Protocol (GGP) was used to communicate route information between core routers on the early Internet. It is a distance-vector protocol that operates in a manner very similar to RIP. Each router periodically sends out its routing table to neighboring routers, so each router can learn the cost, in hops, to reach every network in the autonomous system. GGP is now considered a historical protocol and is no longer part of TCP/IP.
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Version 3.0 - Version Date: September 20, 2005
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