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Overview
The gated Routing Daemon
Chapter 124
Routing Protocols
For routing purposes, networks and gateways are logically grouped into
autonomous system (AS). Companies and organizations that want to
connect to the Internet and form an AS must obtain a unique AS number
from the Internet Assigned Numbers Authority (IANA).
An interior gateway protocol distributes routing information within the
autonomous system. An exterior gateway protocol distributes general
routing information about an autonomous system to other autonomous
systems.
Dividing networks into autonomous systems keeps route changes inside
the autonomous system from affecting other autonomous systems. When
routes change within an autonomous system, the new information need
not be propagated outside the autonomous system if it is irrelevant to
gateways outside the autonomous system.
gated supports the following interior gateway protocols, as defined in
IETF RFCs:
• Routing Information Protocol (RIP) is a common routing protocol
used within an autonomous system. A de facto industry standard, it
is also used by routed, a service distributed by Berkeley. RIP is not
intended for use in wide area network (WAN) applications. There are
currently two versions of RIP implementations: Version 1, as defined
in RFC 1058, and Version 2, as defined in RFC 1388. gated supports
all Version 1 features and most of the features of Version 2. The
following Version 2 features are not supported: RIP management
information base (MIB) route tag, and route aggregation. gated 3.5.9
supports authentication.
• Open Shortest Path First (OSPF), similar to RIP, is a routing
protocol that allows routing information to be distributed between
routers in an autonomous system. Each router on the network
transmits a packet that describes its local links to all other routers.
The distributed database is then built from the collected
descriptions. If a link fails, updated information floods the network,
allowing all routers to recalculate their routing tables at the same
time. OSPF is more suitable than RIP for routing in complex
networks with many routers. gated 3.0 supports most of the features
of OSPF Version 2, as described in RFC 1247, except the IP type of
service (TOS) routing feature. Equal cost multipath routes are
limited to one hop per destination, because the HP-UX kernel
supports only one gateway per route.