CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

MISC IP Routing Commands
- The passive-interface {intf-type intf-num} router subcommand is the simplest solution to
prevent a routing protocol from sending its routing updates out to an interface; but the interface
can still receive (and process) routing updates for a particular routing protocol. There is no point
sending routing updates out an interface where there is no router to receive the routing updates.
Note: Network information for passive interfaces will still be included in routing updates.
- The maximum-paths {max-paths-num} router subcommand defines the number of same
metric parallel paths to a same subnet that can be added to the routing table (and perform load
balancing over the links in a round-robin basis). Its value is ranging from 1 to 6, with the default
of 4. Setting max-paths-num to 1 to disable load balancing. Only values other than 4 will be
shown in the output of the show running-config command.
RT1(config)#router rip
RT1(config-router)#network 192.168.1.0
RT1(config-router)#passive-interface fa1/0
RT1(config-router)#maximum-paths 6
RT1(config-router)#^Z
RT1#
- Since the metrics calculated and used by IGRP (and EIGRP) are very unlikely to be equal, the
variance router subcommand can be used to achieve unequal cost path load balancing.
- The variance {multiplier} router subcommand defines a multiplier. All routes with metric
value less than or equal to lowest metric x variance multiplier are considered equal. Ex: With a
lowest metric of 100 and variance of 2, all routes with a metric ≤ 200 are considered equal.
Note: multiplier value = 1 – 128. The default is 1, which means equal cost path load balancing.
- IGRP (and EIGRP) routers perform load balancing across multiple routes with different metrics
to a same subnet by distributing traffic proportionally to the ratios of the metrics of the unequal
cost paths. The traffic-share min across-interfaces router subcommand tells a router to use
only the lowest metric route even if the routing table has multiple unequal cost routes to a same
subnet due to the variance command.
- With the variance and traffic-share min across-interfaces router subcommands, IGRP is
able to perform instantaneous convergence! Because by having multiple routes to a same
subnet in the routing table, whenever the best route fails, the router can simply select and use the
second best route among the remaining routes.
- The show protocols EXEC command displays all the routed protocols and the interfaces and
addresses that are configured for each protocol.
RT2#sh protocols
Global values:
Internet Protocol routing is enabled
Serial0/0 is up, line protocol is up
Internet address is 192.168.2.2/24
Serial0/1 is up, line protocol is up
Internet address is 192.168.4.1/24
FastEthernet1/0 is up, line protocol is up
Internet address is 192.168.3.1/24
RT2#
90
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