Cisco 3845 Software Guide - Page 663

Using Route Maps to Redistribute Routing Information

Page 663 highlights

Chapter 29 Configuring IP Unicast Routing Configuring Protocol-Independent Features If dynamic default information is not being passed to the system, candidates for the default route are specified with the ip default-network global configuration command. If this network appears in the routing table from any source, it is flagged as a possible choice for the default route. If the router has no interface on the default network, but does have a path to it, the network is considered as a possible candidate, and the gateway to the best default path becomes the gateway of last resort. Using Route Maps to Redistribute Routing Information The switch can run multiple routing protocols simultaneously, and it can redistribute information from one routing protocol to another. Redistributing information from one routing protocol to another applies to all supported IP-based routing protocols. You can also conditionally control the redistribution of routes between routing domains by defining enhanced packet filters or route maps between the two domains. The match and set route-map configuration commands define the condition portion of a route map. The match command specifies that a criterion must be matched. The set command specifies an action to be taken if the routing update meets the conditions defined by the match command. Although redistribution is a protocol-independent feature, some of the match and set route-map configuration commands are specific to a particular protocol. One or more match commands and one or more set commands follow a route-map command. If there are no match commands, everything matches. If there are no set commands, nothing is done, other than the match. Therefore, you need at least one match or set command. Note A route map with no set route-map configuration commands is sent to the CPU, which causes high CPU utilization. You can also identify route-map statements as permit or deny. If the statement is marked as a deny, the packets meeting the match criteria are sent back through the normal forwarding channels (destination-based routing). If the statement is marked as permit, set clauses are applied to packets meeting the match criteria. Packets that do not meet the match criteria are forwarded through the normal routing channel. You can use the BGP route map continue clause to execute additional entries in a route map after an entry is executed with successful match and set clauses. You can use the continue clause to configure and organize more modular policy definitions so that specific policy configurations need not be repeated within the same route map. The switch supports the continue clause for outbound policies. For more information about using the route map continue clause, see the BGP Route-Map Continue Support for an Outbound Policy feature guide for Cisco IOS Release 12.4(4)T at this URL: http://www.cisco.com/en/US/products/ps6441/products_feature_guides_list.html Note Although each of Steps 3 through 14 in the following section is optional, you must enter at least one match route-map configuration command and one set route-map configuration command. OL-23400-01 Cisco ME 3800X and 3600X Switch Software Configuration Guide 29-97

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29-97
Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 29
Configuring IP Unicast Routing
Configuring Protocol-Independent Features
If dynamic default information is not being passed to the system, candidates for the default route are
specified with the
ip default-network
global configuration command. If this network appears in the
routing table from any source, it is flagged as a possible choice for the default route. If the router has no
interface on the default network, but does have a path to it, the network is considered as a possible
candidate, and the gateway to the best default path becomes the gateway of last resort.
Using Route Maps to Redistribute Routing Information
The switch can run multiple routing protocols simultaneously, and it can redistribute information from
one routing protocol to another. Redistributing information from one routing protocol to another applies
to all supported IP-based routing protocols.
You can also conditionally control the redistribution of routes between routing domains by defining
enhanced packet filters or route maps between the two domains. The
match
and
set
route-map
configuration commands define the condition portion of a route map. The
match
command specifies that
a criterion must be matched. The
set
command specifies an action to be taken if the routing update meets
the conditions defined by the match command. Although redistribution is a protocol-independent
feature, some of the
match
and
set
route-map configuration commands are specific to a particular
protocol.
One or more
match
commands and one or more
set
commands follow a
route-map
command. If there
are no
match
commands, everything matches. If there are no
set
commands, nothing is done, other than
the match. Therefore, you need at least one
match
or
set
command.
Note
A route map with no
set
route-map configuration commands is sent to the CPU, which causes high CPU
utilization.
You can also identify route-map statements as
permit
or
deny
. If the statement is marked as a deny, the
packets meeting the match criteria are sent back through the normal forwarding channels
(destination-based routing). If the statement is marked as permit, set clauses are applied to packets
meeting the match criteria. Packets that do not meet the match criteria are forwarded through the normal
routing channel.
You can use the BGP route map
continue
clause to execute additional entries in a route map after an
entry is executed with successful match and set clauses. You can use the
continue
clause to configure
and organize more modular policy definitions so that specific policy configurations need not be repeated
within the same route map. The switch supports the
continue
clause for outbound policies. For more
information about using the route map
continue
clause, see the BGP Route-Map Continue Support for
an Outbound Policy feature guide for Cisco IOS Release 12.4(4)T at this URL:
Note
Although each of Steps 3 through 14 in the following section is optional, you must enter at least one
match
route-map configuration command and one
set
route-map configuration command.