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IP Layer Routing Protocols

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IP Layer

Routing Protocols

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Types of routing Protocols

• Static routing• Dynamic routing

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Static Routing

• Manually configured by Administrator • Administrative distance is 0 or 1 • Destination network should be known • Routing based on next hop IP address or exit

interface • • Secure and fast

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Static Default Route

• • Static default route will be used for unknown destination or for all destination.

• It is used for Internet • It is last preferred route in routing table. • It can be also used on Stub router

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Dynamic Routing Protocol

• Dynamic routing protocols, exchange routing information with the neighbors and build the routing table automatically

• Administrator need to advertise only the directly connected networks

• Any changes in the network topology are automatically updated

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Types of Dynamic Routing Protocol

• Distance Vector Protocol • Link-State Protocol • Advance or Hybrid Protocol

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Distance-Vector Protocol

• Bellman Ford Algorithm• Updates are sent as broadcast• Classfull Routing protocol• Send complete routing table as update • Update are send base on timers.• Routing Loops occur frequently• Ex. RIP, IGRP.

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Link-State Routing Protocol

• SPF or Dijkstra Algorithm• Classless• Sent only incremental / Trigger updates • Updates are sent as multicast• Ex. OSPF, ISIS

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Hybrid Protocol

• Classless• Update are sent as multicast or unicast • Trigger update• Ex. RIPv2, EIGRP, BGP

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Classification of Routing Protocol

• Classfull Routing Protocol – Routing protocol which doesn’t Carry

subnet mask in Routing updates. – Eg. RIP, IGRP. • Classless Routing Protocol – Routing Protocols which carry subnet mask information in routing update – Eg. RIPv2, EIGRP, OSPF, ISIS, BGP

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• Combining the contagious address into one and send to neighbor. •Advantages – – Minimizing the routing table. – – Less use of resources like memory, processor, – bandwidth.

• Two Type of Summarization – – Auto summary

– Manual summary

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Auto Summary

• Also known as “auto summary at network boundary” • Subnet at network boundary will be summarized into • classfull updates • Classfull routing protocol does auto summary by

default and it cant be turn off • Routing protocol like RIPv2, EIGRP, BGPv4 support

auto summary • Routing protocol like OSPF and ISIS doesn’t support

auto summary

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Auto Summary

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Manual summary

• Administrator manually configures Summarization • Summary address contains networks in 2n subnets • It is supported by all classless routing protocols

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• Cisco proprietary• Advance distance-vector routing protocol• Diffusing update algorithm (DUAL)• Administrative distance is 90-internal, 170-external• Classless• Support FLSM, VLSM, CIDR, Auto and Manual summary • Metric = composite metric (32 bits) - Bandwidth, load, delay, reliability & MTU• Updates are sent as multicast( or unicast

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EIGRP Features

• Incremental / triggered update • Fast convergence • Max hops = 224 (default is 100 hops) • Load balancing on 4 equal cost paths (Default) • – Max 16 paths (equal or unequal cost paths) • It supports multiple routed protocols • – (IP, IPX, Apple Talk) • EIGRP uses protocol no 88 • Important Note: IGRP protocol has been

discontinued from IOS ver 12.3 and ab

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Key Technologies• Neighbor discovery

– EIGRP sends hello messages to discover neighbors • Reliable Transport Protocol (RTP)

– Guaranteed delivery of updates to its neighbor • DUAL Algorithm

– It selects the best path and also remembers the • alternate path if any exists • Protocol Dependent Modules (PDM) – – EIGRP supports IPv4, IPv6, IPX, Apple Talk – – For each protocol it has independent module – – Separate hello message, neighbor and topology table

for each of the above protocols

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EIGRP Database

• Neighbor table – List of directly connected routers running EIGRP in same autonomous system • Topology Table - List of all routes learned from its directly connected neighbors • Routing table – List of best paths towards each destination (from the Topology Table)

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EIGRP Database

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Diffusing Update Algorithm- DUAL

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DUAL –stuck in active

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EIGRP packets1. Hello 2. Update3. Query 4. Reply5. ACK

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Initial Routing

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Configuring EIGRP

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Summarization• Auto summary

– EIGRP does auto summary at major logical network • boundary • Manual summary

– EIGRP supports manual summary per interface basis • Summary will be continued till the last specific route

goes down • Summary metric will be the best metric from specific

route • Router of the summary route will create a summary

route pointing to null interface

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Configuring Route Summarization

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EIGRP Load balancing

● Routes with lowest equal metric are installed in the routing table (equal-cost load balancing) ● There can be up to sixteen entries in the routing table for the same destination: – The number of entries is configurable – The default is four • Variance is configured for unequal cost load balancing – Variance is the multiplier to FD of successor – Default is 1(equal cost load balancing)

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Variance Example

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Router Authentication

● Many routing protocols support authentication● Router authenticates the source of each routing update ● Simple password authentication is supported by: – IS-IS – OSPF – RIPv2 ● MD5 authentication is supported by: – OSPF – BGP – EIGRP