Enhanced Inter Gateway Routing Protocol (EIGRP) is Cisco Systems Proprietary protocol based on their original IGRP. EIGRP is a balanced hybrid IP routing protocol, with optimizations to minimize both the routing instability incurred after topology changes, as well as the use of bandwidth and processing power in the router. EIGRP has Protocol-Dependent Modules that can deal with AppleTalk and IPX as well as IP. The advantage with this is that only one routing process need run instead of a routing process for each of the protocols. EIGRP provides loop-free operation and almost instant simultaneous synchronization of routers.

Inter-Autonomous System: Inter-Autonomous System routing protocols are designed to connect lager networks or Autonomous Systems (AS) together and allow for muitiple Autonomous Systems to network. One example for the need of an inter-autonomous system protocol is to connect two or more Internet Service Providers (ISP) together so there customer can connect to each other. Without getting in to too much detail both “Link State & Distance Vector” protocols are considered intra-autonomous system protocols as they are designed to just route traffic in a singal AS. Inter-Autonomous System protocols main goal is to propergate the intra-autonomous system information between different autonomous systems.

BGP4 (Border Gateway Protocol Version 4):

Border Gateway Protocol is the backbone routing protocol for most of the internet and allows for peering and carrier networks to connect. BGP is explained as a path vector protocol. With BGP the policy or attributes for making the actual route selections among the interconnected autonomous systems is based on Weight ,Local preference, Multi-exit discriminator, Origin, AS path, Next hop, & Community. BGP information is propagated through the network by exchanges of BGP messages (4 types: Open, Update, Notification, & Keep Alive) between peers. Another key feature to BGP is that is supports Classless Inter Domain Routing (CIDR) with the support of CIDR BGP can reduce the size of the Internet routing tables. BGP neighbors exchange full routing information when the TCP (port 179) connection between neighbors is first established. When changes to the routing table accrue, the BGP routers send to their neighbors only those routes that have changed. BGP routers do not send periodic routing updates and advertise only the optimal paths to a destination.