10-04-2017, 09:08 PM
Hybrid Routing Protocols
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EIGRP (Enhanced IGRP)
advanced distance vector protocol.
Cisco proprietary.
maintain neighbor relationship using hello protocol.
send hello every 5 sec. on fast page link (>1.54Mbps).
send hello every 60 sec. on slow page link (<1.54Mbps).
dead interval = 3 * hello interval.
rapid convergence by using DUAL algorithm ( store a backup route for each best route).
support multiple network layer protocols (IP, IPX, Apple talk).
support equal and unequal load balancing between many paths to the same destination network.
differentiate between internal and external routes.
admin. Distance = 90 for internal routes.
admin. Distance = 170 for external routes.
symbol ( D ) in routing table.
EIGRP (cont.)
Max. hop count = 224.
Classless
Reliable protocol.
Have the same operation in all topologies.
Compatible with IGRP if the EIGRP and IGRP in the same AS.
EIGRP metric is stored in 32 bits.
IGRP metric is stored in 24 bits.
EIGRP metric = 256 * IGRP metric.
EIGRP routers to be neighbors:
1- Must have the same AS number.
2- Must have the same K-values.
EIGRP terminologies
Neighbor table: List of all neighbors.
Topology table: list of all routes to destination networks.
Routing table: list of best routes to all destination networks.
Successor ( S ): best route to destination network , stored in routing table and topology.
Feasible successor (FS): backup route to destination network, stored in topology table.
Feasible distance (FD): metric between source and destination network.
Advertised distance (AD): metric between my neighbor and the destination network .
FD = next hop metric + AD.
Variable Length Subnet Mask (VLSM)
VLSM means that in a single class A, B, or C network, more than one subnet mask is used.
VLSM allows some subnets to be smaller and some subnets to be larger, which reduce the waste in IP addresses.
VLSM allows you to apply different subnet masks to the same class address.
Steps :
- begin with the largest subnet
- continue giving addresses with the suitable subnet mask
VLSM example
For s1, s2 , s3 to support 60 host we need 6 bits
so subnet mask is 255.255.255.192
hop count = 256-192 = 64
s1 address 192.168.1.0 /26
s2 address 192.168.1.64 /26
s3 address 192.168.1.128 /26
starting from address 192.168.1.192 give addresses to s4 , s5 , s6
2 hosts need 2 bits
new subnet mask is 255.255.255.252 , hop count = 256-252 = 4
s4 address 192.168.1.192 /30
s5 address 192.168.1.196 /30
s6 address 192.168.1.200 /30