Advance Routing Egp

3.

What is the history and what were the driving factors behind the development of the EGP routing protocol?

4.

What is the industry acceptance and view of this protocol?

When the department of defense’s DARPANET was originally implemented, they ran into a number of problems with the expansion of the network as more facilities and institutions were given the ability and permission to participate in it. While the GGP protocol provided a means for which the routers from each facility to communicate (in the form of multiple autonomous systems communicating with each other), routing protocols began to evolve and thus allowed for different software and hardware to be installed in each individual autonomous system. This created a number of problems including the lack of an ability to do fault isolation because of the different protocols and software being used, as well as this software not being able to be adapted to expansion because of it having to communicate with multiple other pieces of software. With this lack of an ability for ARPANET to expand, researchers also found that the need to advertise which protocol a router is using to all other routers on the network is unneeded and could possibly facilitate attacks on the source network. Both of these issues were thought about and began to be remedied in RFC 827 which stated these problems and was the first to propose that the internet would expand into a large number of autonomous systems which needed a common protocol to allow communication between a large number of autonomous systems. Exterior Gateway protocol was originally designed and implemented in the early 1980’s with the first Request for Comments regarding the protocol being published in October of 1982. It was one of the original protocols used in the ARPANET and DARPANET military networks but was obsoleted with the creation and widespread acceptance and use of Border Gateway Protocol.

Before modern internet was implemented, EGP allowed for transport of datagrams between manual systems and autonomous systems without interruption of service to the user. This was mainly done between core routers and non-core routers which were the main backbone to the early internet as used within ARPANET and DARPANET. Information was able to be exchanged between the core routers and non-core routers which encompassed individual autonomous systems (1), while still providing net reachability information between the autonomous systems through which it traversed.(6) With this traversal through multiple types of networks, the number of networks and autonomous systems “are to be transparent to the end-user (1).” In other words, when a datagram is being transmitted between multiple networks to reach a final destination, the user should see little lag or latency, and see the traversal across all of the multiple networks that the datagram traverses across as a single pathway through a flat internet. This is to prevent the need for multiple protocols, but rather to inspire the creation of a single protocol that had similar characteristics and could be implemented on a large scale basis between autonomous systems. Similar to BGP, EGP uses polling in the form of Hello and I-Heard-You messages which ensure that neighboring routers are still available and able to accept incoming or outgoing messages. EGP also allows for routing tables to be sent between routers to ensure that a full database is kept for paths to all attached networks, as well as metrics to connected networks, similar to BGP. EGP and its immediate successor, EGP2 are now used in the transmission of routing tables in BGP, thus making it a still existing protocol but an obsolete one. (2) *EGP will transmit the same way BGP will: by advertising its attached nodes to its neighbors (routing database style), making it a link state protocol.

Overall, EGP was used by the ARPANET and DARPANET defense networks in the early days of routing and network connectivity between autonomous systems. With the implementation and widespread standardization of BGP, EGP has been obsoleted and is currently unused within industry. This is because of the additional features that BGP added to EGP. The main problem with EGP is that it assumes that the network it is attached to, in this case the internet, is structured in a tree type topology. Therefore, it tried to recreate the routing table and metrics to each network within its routing database by mapping the network in a tree form (See appendix a for examples.) It is obvious that the internet is by no means a tree type structure, and this was the driving factor for obsolescing EGP and implementing BGP. BGP has the ability to map the internet in whatever topology actually existed, rather than the assumed one. At the moment, BGP still uses EGP in some forms to discover networks external from the network that it is currently being run on. (4)

An example of the assumed network structure as seen by EGP (3)

A network with the ability to be processed by BGP. Not that there is not a definite tree like structure here.(3)

[1] http://www.tcpipguide.com/free/t_TCPIPExteriorGatewayProtocolEGP.htm [2] http://tools.ietf.org/html/rfc1772 [3] http://homepages.uel.ac.uk/u0225867/website/egp_bgp.htm [4] http://www.faqs.org/rfcs/rfc1771.html [5] http://www.faqs.org/rfcs/rfc1092.html [6] http://tools.ietf.org/html/rfc904