Technical data

Gateway Routing Daemon (GATED) Configuration Reference
A.11 Definition Statements
The following list describes each statement in the example:
• The options statement tells the system to generate a default route when it
peers with an EGP or BGP neighbor.
• The autonomoussystem statement tells GATED to use AS number 249 for
EGP and BGP.
• The
interface statement tells GATED not to mark interface 128.66.12.2 as
down even if it sees no traffic.
• The
martians statement prevents routes to 0.0.0.26 from ever being accepted.
A.12 Protocol Overview
Unicast routing protocols allow packets to be routed to one destination. All
routing protocols determine the ‘‘best’’ route to each destination, and they
distribute routing information among the systems on a network. Routing
protocols are divided into two general groups: interior (or intradomain routing)
protocols and exterior (or interdomain routing) protocols. GATED software
combines management of the interior and exterior routing protocols in one
software daemon.
A.12.1 Interior Routing Protocols
Interior protocols are used to exchange reachability information within an
autonomous system (AS). They are referred to as a class by the acronym IGP.
There are several interior protocols:
• RIP
The Routing Information Protocol, Version 1 and Version 2, is the most
commonly used interior protocol. RIP selects the route with the lowest
metric as the best route. The metric is a hop count representing the number
of gateways through which data must pass to reach its destination. The
longest path that RIP accepts is 15 hops. If the metric is greater than 15, a
destination is considered unreachable and GATED discards the route. RIP
assumes the best route is the one that uses the fewest gateways i.e., the
shortest path, not taking into account congestion or delay on route.
The RIP version 1 protocol is described in RFC 1058 and the RIP version 2
protocol is described in RFC 1723.
• OSPF
Open Shortest Path First is a link-state protocol. OSPF is better suited than
RIP for complex networks with many routers. OSPF provides equal cost
multipath routing.
OSPF is described in RFC 1583, the MIB is defined in RFC 1253. Other
related documents are RFC 1245, RFC 1246 and RFC 1370.
A.12.2 Exterior Routing Protocol
Exterior protocols are used to exchange routing information between autonomous
systems. Exterior protocols are only required when an autonomous system
must exchange routing information with another autonomous system. Routers
within an autonomous system run an interior routing protocol like RIP. Only
those gateways that connect an autonomous system to another autonomous
system need to run an exterior routing protocol. There are two exterior protocols
currently supported by GATED:
A–16 Gateway Routing Daemon (GATED) Configuration Reference