HP-UX Reference (11i v3 07/02) - 4 File Formats (vol 8)

g
gated.conf(4) gated.conf(4)
Nonrouting by protocol
proto default | aggregate
restrict ;
proto default | aggregate
[ metric metric ] {
route_filter [ restrict |(metric metric )];
};
These protocols may only be referenced by protocol.
default
Refers to routes created by the gendefault option. It is recommended that route generation be
used instead.
aggregate
Refers to routes synthesized from other routes when the aggregate and generate statements
are used. See the section on Route Aggregation for more information.
Exporting by AS path
proto proto | all aspath aspath_regexp
origin any |([igp ][egp ][incomplete ])
restrict ;
proto proto | all aspath aspath_regexp
origin any |([igp ][egp ][incomplete ])
[ metric metric ] {
route_filter [ restrict |(metric metric )];
};
When BGP is configured, all routes are assigned an AS path when they are added to the routing table. For
all interior routes this AS path specifies IGP as the origin and no ASes in the AS path (the current AS is
added when the route is exported). For EGP routes this AS path specifies EGP as the origin and the source
AS as the AS path. For BGP routes, the AS path is stored as learned from BGP.
AS path regular expressions are documented in the section on Matching AS paths.
Exporting by route Tag
proto proto | all tag tag restrict ;
proto proto | all tag tag
[ metric metric ] {
route_filter [ restrict |(metric metric )];
};
Both OSPF and RIP version 2 currently support tags, all other protocols always have a tag of zero. The
source of exported routes may be selected based on this tag. This is useful when routes are classified by tag
when the are exported into a given routing protocol.
Route Aggregation
Route aggregation is a method of generating a more general route given the presence of a specific route. It
is used, for example, at an autonomous system border to generate a route to a network to be advertised via
EGP given the presence of one or more subnets of that network learned via RIP. Older versions of GateD
automatically performed this function, generating an aggregate route to a natural network (using the old
Class A, B and C concept) given an interface to a subnet of that natural network. However that was not
always the correct thing to do, and with the advent of classless interdomain routing it is even more fre-
quently the wrong thing to do, so aggregation must be explicitly configured. No aggregation is performed
unless explicitly requested in an aggregate statement.
Route aggregation is also used by regional and national networks to reduce the amount of routing informa-
tion passed around. With careful allocation of network addresses to clients, regional networks can just
announce one route to regional networks instead of hundreds.
Aggregate routes are not actually used for packet forwarding by the originator of the aggregate route, only
by the receiver (if it wishes). A router receiving a packet which does not match one of the component routes
which led to the generation of an aggregate route is supposed to respond with an ICMP network unreach-
able message. This is to prevent packets for unknown component routes from following a default route into
another network where they would be forwarded back to the border router, and around and around again
and again, until their TTL expires. Sending an unreachable message for a missing piece of an aggregate is
HP-UX 11i Version 3: February 2007 − 48 − Hewlett-Packard Company 175