Installing and Administering Internet Services

Chapter 8 239
Configuring gated
Overview
organizations that wish to connect to the Internet and form an AS must
obtain a unique AS number from the Internet Assigned Numbers
Authority.
An interior gateway protocol is used to distribute routing information
within the autonomous system. An exterior gateway protocol is used to
distribute 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:
• RIP (Routing Information Protocol) 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 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. (Note that authentication is now
supported, with gated version 3.5.)
• OSPF (Open Shortest Path First), like 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. The following version 2 feature is not
supported: IP type of service (TOS) routing. Equal cost multipath
routes are limited to one hop per destination, because the HP-UX
kernel supports only one gateway per route.
• HELLO was designed to work with routers called “Fuzzballs.” Most
installations use RIP or OSPF instead of HELLO.