Route Maps, Prefix Lists, and Authoritative Distance
Route maps, IP prefix lists, and authoritative ambit (AD) charge be able-bodied accepted to do well
with avenue redistribution capacity on the CCIE Acquisition and Switching accounting exam. This section
focuses on the accoutrement themselves, followed by advantage of avenue redistribution.
Configuring Avenue Maps with the route-map Command
Route maps accommodate programming argumentation agnate to the If/Then/Else argumentation apparent in added programming
languages. A distinct avenue map has one or added route-map commands in it, and routers process
route-map commands in consecutive adjustment based on arrangement numbers. Each route-map command
has basal analogous parameters, configured with the appropriately called bout command. (To
match all packets, the route-map article artlessly omits the bout command.) Each route-map
command additionally has one or added alternative set commands that you can use to dispense information—
for instance, to set the metric for some redistributed routes. The accepted rules for avenue maps are
as follows:
■ Each route-map command charge accept an absolutely configured name, with all commands that
use the aforementioned name actuality allotment of the aforementioned avenue map.
■ Each route-map command has an activity (permit or deny).
■ Each route-map command in the aforementioned avenue map has a different arrangement number, allowing
deletion and admittance of distinct route-map commands.
■ Back a avenue map is acclimated for redistribution, the avenue map processes routes taken from the
then-current acquisition table.
■ The avenue map is candy sequentially based on the arrangement numbers.
■ Already a accurate avenue is akin by the avenue map, it is not candy above that matching
route-map command (specific to avenue redistribution).
■ Back a avenue is akin in a route-map statement, if the route-map command has a permit
parameter, the avenue is redistributed (specific to avenue redistribution).
■ Back a avenue is akin in a route-map statement, if the route-map account has a deny
parameter, the avenue is not redistributed (specific to avenue redistribution).
302 Affiliate 10: IGP Avenue Redistribution, Avenue Summarization, and Default Routing
Route maps can be ambagious at times, abnormally back application the abjure advantage on the route-map
command. To advice accomplish abiding the argumentation is bright afore accepting into redistribution, Amount 10-1
shows a argumentation diagram for an archetype avenue map. (This archetype is apish to authenticate some
nuances of avenue map logic; a better, added able avenue map could be created to accomplish the same
results.) In the figure, R1 has eight loopback interfaces configured to be in chic A networks 32
through 39. Amount 10-1 shows how the apish route-map captious would activity the routes.
Figure 10-1 Avenue Map Argumentation Example
First, a few clarifications about the acceptation of Amount 10-1 are in order. The top of the figure
begins with the set of affiliated networks (32 through 39), labeled with a “B,” which is the set of
routes still actuality advised for redistribution. Moving bottomward the figure, four abstracted route-map
commands sit central this distinct avenue map. Each route-map article (the article includes the
underlying bout and set commands) in about-face moves routes from the account of accessible routes (“B”)
34, 35, 36, 38
Not Matched
End of List: adumbrated abjure all
Null
route-map captious abjure 40
match ip abode 33
B
B
33, 34, 35, 36, 38
Not Matched
route-map captious abjure 33
match ip abode d-38-p39
B
33, 34, 35, 36, 38, 39
Not Matched
route-map captious admittance 25
match ip abode d-36-p-37
B
33, 34, 35, 36, 37, 38, 39
Not Matched
Matched
32
Permit route-map captious admittance 10
match ip abode 32
B
B 32, 33, 34, 35, 36, 37, 38, 39
A 32, 37 C 33, 34, 35, 36, 38, 39
A 32, 37 C 33, 39
A 32, 37 C 39
A 32, 37 C null
A 32 C null
A The set of routes to redistribute
B Routes for which no decision
has been fabricated yet
C The set of routes that are not
redistributed
Matched
37
Matched
39
Permit
Deny
Matched
33
Deny
Deny
ACL 32:
Permits Arrangement 32
Default Abjure Any at End
ACL 33:
Permits Arrangement 33
Default Abjure Any at End
ACL d-36-p-37:
Denies Arrangement 36
Permits Arrangement 37
Default Abjure Any at End
ACL d-38-p-39:
Denies Arrangement 38
Permits Arrangement 39
Default Abjure Any at End
Route Maps, Prefix Lists, and Authoritative Ambit 303
to either the account of routes to redistribute (“A”) or the account to not redistribute (“C”). By the bottom
of the figure, all routes will be acclaimed as either to be redistributed or not to be redistributed.
The avenue map chooses to redistribute a avenue alone if the route-map command has a permit
option; the alone time a route-map article chooses to not redistribute a avenue is back the clause
has a abjure option. Ignoring the analogous argumentation for a moment, the aboriginal two route-map commands
(sequence numbers 10 and 25) use the admittance option. As a aftereffect of those clauses, routes are either
added to the account of routes to redistribute (“A”) or larboard in the account of applicant routes (“B”). The third
and fourth clauses (sequence numbers 33 and 40) use the abjure option, so those clauses cause
routes to be either added to the account of routes to not redistribute (“C”), or larboard in the account of candidate
routes (“B”). In effect, already a route-map article has akin a route, that avenue is flagged either
as to be redistributed or as not to be redistributed, and the avenue is no best candy by the
route map.
One point that can sometimes be abashed is that if a avenue is denied by an ACL acclimated by a match
command, it does not beggarly that the avenue is prevented from actuality redistributed. For instance, the
match ip abode 32 command in article 10 refers to ACL 32, which has one absolute access
control access (ACE) that matches arrangement 32, with a admittance action. Of course, ACL 32 has an
implied abjure all at the end, so ACL 32 permits arrangement 32, and denies 33 through 39. However,
denying networks 33 through 39 in the ACL does not beggarly that those routes are not
redistributed—it artlessly agency that those routes do not bout route-map article 10, so those
routes are acceptable for application by a after route-map clause.
The afterward account summarizes the key credibility about avenue map argumentation back acclimated for redistribution:
■ route-map commands with the admittance advantage either account a avenue to be redistributed or leave
the avenue in the account of routes to be advised by the abutting route-map clause.
■ route-map commands with the abjure advantage either clarify the avenue or leave the avenue in the list
of routes to be advised by the abutting route-map clause.
■ If a clause’s bout commands use an ACL, an ACL bout with the abjure activity does not
cause the avenue to be filtered. Instead, it aloof agency that avenue does not bout that particular
route-map clause.
■ The route-map command includes an adumbrated abjure all article at the end; to configure a permit
all, use the route-map command, with a admittance action, but after a bout command.
Route Map bout Commands for Avenue Redistribution
Route maps use the bout command to ascertain the fields and ethics acclimated for analogous the routes
being processed. If added than one bout command is configured in a distinct route-map clause, a
route is akin alone if all the bout commands’ ambit bout the route. The argumentation in each
304 Affiliate 10: IGP Avenue Redistribution, Avenue Summarization, and Default Routing
match command itself is almost straightforward. Table 10-2 lists the bout command options
when acclimated for IGP avenue redistribution.
Route Map set Commands for Avenue Redistribution
When acclimated for redistribution, avenue maps accept an adumbrated action—either to acquiesce the avenue to be
redistributed or to clarify the avenue so that it is not redistributed. As declared beforehand in this chapter,
that best is adumbrated by the admittance or abjure advantage on the route-map command. Avenue maps can
also change advice about the redistributed routes by application the set command. Table 10-3 lists
the set command options back acclimated for IGP avenue redistribution.
Table 10-2 bout Command Options for IGP Redistribution
match Command Description
match interface interface-type interface-number
[... interface-type interface-number]
Looks at approachable interface of
routes
*match ip abode {[access-list-number | access-list-name] |
prefix-list prefix-list-name}
Examines avenue prefix and prefix
length
*match ip next-hop {access-list-number | access-list-name} Examines route’s next-hop
address
*match ip route-source {access-list-number | access-listname}
Matches announcement router’s IP
address
match metric metric-value Matches route’s metric
match route-type {internal | alien [type-1 | type-2] | level-1 |
level-2}
Matches avenue type
match tag tag-value [...tag-value] Tag charge accept been set earlier
*Can advertence assorted numbered and called ACLs on a distinct command.
Table 10-3 set Command Options for IGP Redistribution
set Command Description
set akin {level-1 | level-2 | level-1-2 | stub-area |
backbone}
Defines database(s) into which the avenue is
redistributed
set metric metric-value Sets the route’s metric for OSPF, RIP, and
IS-IS
set metric bandwidth adjournment believability loading mtu Sets the IGRP/EIGRP route’s metric values
set metric-type {internal | alien | type-1 | type-2} Sets blazon of avenue for IS-IS and OSPF
set tag tag-value Sets the unitless tag amount in the route