Linux in a Nutshell, 6th Edition

Gateways and Routing

Gateways are hosts responsible for exchanging routing information and forwarding data from one network to another. Each portion of a network that is under a separate local administration is called an autonomous system (AS). Autonomous systems connect to each other via exterior gateways. An AS also may contain its own system of networks, linked via interior gateways.

Gateway protocols

Gateway protocols include:

EGP (Exterior Gateway Protocol)BGP (Border Gateway Protocol)

Protocols for exterior gateways to exchange information

RIP (Routing Information Protocol)

Interior gateway protocol; most popular for LANs

Hello ProtocolOSPF (Open Shortest Path First)

Interior gateway protocols

Routing daemons

While most networks will use a dedicated router as a gateway, routing daemons like quagga and GNU Zebra, can be run on a host to make it function as a gateway. These replace the older gated daemon. Only one of them can run on a host at any given time. They allow a host to function as both an exterior and interior gateway and simplify routing configuration by combining the protocols RIP, Hello, BGP, EGP, and OSPF into a single package. We do not cover quagga or GNU Zebra in this book.

routed, a network routing daemon that uses RIP, allows a host to function only as an interior gateway, and manages the Internet routing tables. For more details on routed, see Chapter 3.

Routing tables

Routing tables provide information needed to route packets to their destinations. This information includes ...