HP-UX Reference (11i v1 00/12) - 4 File Formats (vol 8)
__________________________________________________________________________________________________________________________________________________________________________________________________
__________________________________________________________________________________________________________________________________________________________________________________________________
STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man4/!!!intro.4
________________________________________________________________
___ ___
g
gated.conf(4) gated.conf(4)
generate (control) defines which routes to generate.
Preference
Preference is the value GateD uses to order preference of routes from one protocol or peer over another.
Preference can be set in the GateD configuration files in several different configuration statements. Prefer-
ence can be set based on network interface over another, from one protocol over another, or from one
remote gateway over another. Preference may not be used to control the selection of routes within an igp,
this is accomplished automatically by the protocol based on metric. Preference may be used to select routes
from the same egp learned from different peers or autonomous systems. Each route has only one prefer-
ence value associated with it, even though preference can be set at many places in the configuration file.
Simply, the last or most specific preference value set for a route is the value used. (See Glossary of
Terms: Preference.) The preference value is an arbitrarily assigned value used to determine the order of
routes to the same destination in a single routing database. The active route is chosen by the lowest prefer-
ence value. Some protocols implement a second preference (preference2), sometimes referred to as a tie-
breaker.
Selecting a route
• The route with the best (numerically smallest) preference is preferred.
• If the two routes have the same preference, the route with the best (numerically smallest) prefer-
ence2 (also known as a tie-breaker) is preferred.
• A route learned from a igp is preferred to a route learned from an egp. Least preferred is a route
learned indirectly by an igp from an egp.
• If AS path information is available,it is used to help determine the most preferred route.
• A route with an AS path is preferred over one without an AS path.
• If the AS paths and origins are identical, the route with the lower metric is preferred.
• A route with an AS path origin of igp is preferred over a route with an AS path origin of egp.
Least preferred is an AS path with an unknown origin.
• A route with a shorter AS path is preferred.
• If both routes are from the same protocol and AS, the one with the lowest metric is preferred.
• The route with the lowest numeric next-hop address is used.
Assigning preferences
A default preference is assigned to each source from which GateD receives routes. Preference values range
from 0 to 255 with the lowest number indicating the most preferred route.
The following table summarizes the default preference values for routes learned in various ways. The table
lists the statements (some of these are clauses within statements) that set preference, and shows the types
of routes to which each statement applies. The default preference for each type of route is listed, and the
table notes preference precedence between protocols. The narrower the scope of the statement, the higher
precedence its preference value is given, but the smaller the set of routes it affects.
Preference Of Defined by Statement Default
direct connected networks interface 0
OSPF routes ospf 10
IS-IS level 1 routes isis level 1 15
IS-IS level 2 routes isis level 2 18
internally generated default gendefault 20
redirects redirect 30
routes learned via route socket kernel 40
static routes from config static 60
ANS SPF (SLSP) routes slsp 70
HELLO routes hello 90
RIP routes rip 100
point-to-point interface 110
routes to interfaces that are down interfaces 120
Section 4−−74 − 3 − HP-UX Release 11i: December 2000
___
___