Successor and Feasible successor
A successor is neighbor router that is used to forward the packets and is the least–cost route to the destination network.Feasible distance is the lowest calculated metric to the destination.This is listed in the routing table entry.
In EIGRP,DUAL converges quickly after the topology changes and uses the backup path to other router known as feasible successor.A feasible successor is a neighbor which provides the loop free path to the same network as the successor.
The successor,feasible distance and feasible successor placed with their reported distance in its EIGRP topology table and this can be display by this command-
Router # show ip eigrp topology
Disabling automatic summarization
EIGRP automatic summarizes major network boundaries using the command auto-summary.In EIGRP,DUAL takes all the neighbor adjacencies and reestablishes them and all EIGRP neighbor will immediately send out new updates that will not automatically summarized.
Manual summarization
EIGRP can be configured to summarize the routes,whether the automatic summarization is enable or not.EIGRP is classless routing protocol and include the subnet mask in the routing updates,manual summarization include supernet routes that is a aggregation of multiple classful network address.
To calculate the EIGRP summary route
To calculate the summary route for IGRP use the following steps-
Write all the network that is to be summarized in the binary form.
For the subnet mask,start from the left most bits.
Selects the match bits from left to right.
Stop at the column where the bits don’t match.
Count the number of left most matching bits.This number is the network bits or the subnet mask.
To find the network address for the summarization after the matching bits add all bits 0 to the end of 32 bit.
For example
192.168.1.0 – 11000000.10101000.00000001.00000000
192.168.2.0 – 11000000.10101000.00000010.00000000
192.168.3.0 – 11000000.10101000.00000011.00000000
The first 22 bits are matching so the subnet mask will be /22 that is
255.255.252.0
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