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

- When a link to a neighbor fails, all successor and feasible successor routes through that neighbor
enter into active state and the router is required to perform route computation.
- The xxx and yyy in the via A.B.C.D (xxx/yyy), interface entry in the show ip eigrp topology
EXEC command represent feasible distance and advertised distance respectively.
- EIGRP uses the following 5 types of packets:
Hellos Used for neighbor discovery. Do not require acknowledgement.
Updates Used to tell a newly discovered neighbor the reachability of destination networks.
Requires acknowledgment.
Queries Used to ask for a replacement route when there is no feasible successor to a network.
Requires acknowledgment.
Replies Used to response to query packets to tell the originator not to recompute the route as
there is feasible successor. Requires acknowledgment.
ACKs Used to acknowledge updates, queries, and replies.
- The EIGRP passive-interface {intf-type intf-num} router subcommand prevents an interface
from sending and receiving Hello packets, which eventually stop it from forming adjacencies and
exchanging routing updates with other routers which reside on the passive interface subnet.
- RIP passive interfaces prevent the sending but allow the receiving of routing updates. Hence the
router can still learn about the networks advertised by other routers.
EIGRP passive interfaces neither send nor receive routing updates. Additionally no neighbor
relationship will be formed, as EIGRP passive interfaces suppress the exchange of Hello packets.
- EIGRP performs autosummarization in discontiguous networks by default, and some networks
might not work due to this feature. The best practice is disable autosummarization and performs
manual summarization with ip summary-address interface subcommand when necessary.
EIGRP autosummarization can be disabled with the no auto-summary router subcommand.
Router(config)#router eigrp 10
Router(config-router)#network 10.0.0.0
Router(config-router)#network 172.16.0.0
Router(config-router)#no auto-summary
Note: classful network addresses are used in EIGRP (and IGRP) configuration.
- The maximum-paths {num} router subcommand defines the total number of links allowed for
equal-cost path load balancing. Its value is ranging from 1 to 6, with the default of 4.
The variance router subcommand can be used to achieve unequal cost path load balancing.
- EIGRP (and IGRP) has a default maximum hop count of 100, but it can be changed to 255.
Normally it is unnecessary to change the value, as hop count isn’t used in the path metric
calculation. It is only being used to limit the scope of an autonomous system.
Router(config)#router eigrp 10
Router(config-router)#metric maximum-hops ?
Hop count
110
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yapchinhoong@hotmail.com