Technical data

Gateway Routing Daemon (GATED) Configuration Reference
A.12 Protocol Overview
• EGP
Exterior Gateway Protocol: Originally EGP reachability information was
passed into ARPANET/MILNET ‘‘core’’ gateways where the best routes
were chosen and passed back out to all connected autonomous systems. As
the Internet moved toward a less hierarchical architecture, EGP, an exterior
routing protocol which assumes a hierarchical structure, became less effective.
The EGP protocol is described in RFC 827 and RFC 904.
• BGP
Border Gateway Protocol is replacing EGP as the exterior protocol of choice.
BGP exchanges reachability information between autonomous systems, but
provides more capabilities than EGP. BGP uses path attributes to provide
more information about each route as an aid in selecting the best route. Path
attributes may include, for example, administrative preferences based on
political, organizational, or security (policy) considerations in the routing
decision. BGP supports nonhierarchical topologies and can be used to
implement a network structure of equivalent autonomous systems.
BGP version 1 is described in RFC 1105; version 2 in RFC 1163; version 3
in RFC 1267; and version 4 in RFC 1771. The version 3 MIB is described
in RFC 1269. The three documents, RFC 1164, RFC 1268, and RFC 1772,
describe the application of versions 2, 3, and 4 in the Internet. A protocol
analysis of an experience with BGP version 3 is available in RFC 1265 and
RFC 1266. RFC 1397 talks about advertising a default route in BGP version
2 and 3.
BGP version 4 is described in RFC 1771. The BGP V4 MIB implemented
by GATED is draft standard, but is scheduled to go to standard. Other
references for BGP are: RFC 1997 (BGP Communities), RFC 1966 (BGP
Route Reflection), RFC 1966 (BGP AS Confederations), and RFC 1403
(BGP–OSPF interaction). A useful application document is: RFC 1998 (An
Application of the BGP Community Attribute in Multi-home Routing).
A.12.3 Router Discovery Protocol
The Router Discovery protocol is used to inform hosts of the availability of other
hosts to which it can send packets. Router Discovery is used to supplement a
statically configured default router. This is the preferred protocol for hosts to run.
They are discouraged from wiretapping routing protocols. Router Discovery is
described in RFC 1256
A.12.4 ICMP
On systems without the BSD routing socket, GATED listens to ICMP messages
received by the system. Processing of ICMP redirect messages is handled by the
redirect statement.
A.12.5 Redirect
The redirect code process ICMP or ISO redirects learned by monitoring ICMP
messages, or via the routing socket on systems that support it. It processes
the redirect request and decides whether to accept the redirect. If the redirect
is accepted, a route is installed in the GATED routing table with the protocol
redirect. Redirects are deleted from the routing table after 3 minutes.
Gateway Routing Daemon (GATED) Configuration Reference A–17