Practical TCP/IP and Ethernet Networking- P28: The transmitter encodes the information into a suitable form to be transmitted over the communications channel. The communications channel moves this signal as electromagnetic energy from the source to one or more destination receivers. The channel may convert this energy from one form to another, such as electrical to optical signals, whilst maintaining the integrity of the information so the recipient can understand the message sent by the transmitter | Internet layer protocols 117 Core Gateway Figure Application of routing protocols In a simple AS consisting of only a few physical networks the routing function provided by IP may be sufficient. In larger ASs however sophisticated routers using adaptive routing algorithms may be needed. These routers will communicate with each other using interior gateway protocols such as RIP Hello IS-IS or OSPF. Routers in different ASs however cannot use IGPs for communication for more than one reason. Firstly IGPs are not optimized for long-distance path determination. Secondly the owners of ASs particularly Internet service providers would find it unacceptable for their routing metrics which include sensitive information such as error rates and network traffic to be visible to their competitors. For this reason routers that communicate with each other and are resident in different ASs communicate with each other using exterior gateway protocols. The routers on the periphery connected to other ASs must be capable of handling both the appropriate IGPs and EGPs. The most common exterior gateway protocol currently used in the TCP IP environment is border gateway patrol BGP the current version being BGP-4. A third type of routing protocol is used by the core routers gateways that connect users to the Internet backbone. They use gateway to gateway protocols GGP to communicate with each other. Interior gateway protocols The protocols that will be discussed are RIPv2 routing information protocol version 2 EIGRP enhanced interior gateway routing protocol and OSPF open shortest path first . RIPv2 RIPv2 originally saw the light as RIP RFC 1058 1388 and is one of the oldest routing protocols. The original RIP had a shortcoming in that it could not handle variable-length 118 Practical TCP IP and Ethernet Networking subnet masks and hence could not support CIDR. This capability has been included with RIPv2. RIPv2 is a distance vector routing protocol where each router using a .
