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Chapter Overview

Routing Principles Building Routing Tables

Routing Protocols

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Key to the network connection info Contract routing tables dynamically Costs are CPU time and network traffics

IGP and EGP (Interior/Exterior gateway protocols)

Routing Basics

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Administrative Distances (AD)

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It is use to rate the trustworthiness of routing info received on one router from its neighboring routers

A number between 0 to 255 0 is the most trusted 255 == no traffic should go there

Entering to routing table if two routers both can reach an IP Rule #1, go with a lower AD Rule #2, if the two ADs are the same, do hop

count, etc cost/metrics calculations If cost/metrics calculations are all the same, do a

“Load Balance” test by sending messages to the two routers

AD numbers

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Three classes of routing protocols

Distance vector Count the number of routers (hops) between two points

Link State Router has 3 tables: (1) directly attached neighbors, (2)

table used to determines the topology of the entire internetwork, (3) actual routing table

It knows more about the network than Distance Vector It use an algorithm to calculate the shortest path

Hybrid Combines the two, Cisco proprietary protocol

No “best” approach6

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Dynamic Routing

Distance-Vector Routing

Routing by rumor A router passes COMPLETE routing-table to

neighboring routers The received routing table is combined with a

router’s own routing table without verification Use hop count to determine routing, then AD,

then “load balancing” Know the directly connected networks initially Build the tables afterward

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Example, initial routing tables

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Example, populated

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RIP Characteristics RIP: the acronym for Routing Information

Protocol Most common interior gateway protocol (IGP)

in the TCP/IP suite Originally designed for UNIX systems as a

daemon called routed Eventually ported to other platforms Standardized in Request for Comments (RFC)

1058 Updated to version 2, published as RFC 2453

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RIP Communications

RIP routers initiate communications when starting up by broadcasting a request message on all network interfaces.

All RIP routers receiving the broadcast respond with reply messages containing their entire routing table.

The router receiving the replies updates its own routing table with the information in the reply messages.

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RIP Version 1 Message Format

Refresh every 30 seconds

3 minutes == out

Not support subnet mask

Max hop count 15 – used by small networks only

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RIP Version 2 Message Format

Message are sent using UDP (user Datagram Protocol)

Port 520

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RIP 2

From http://www.tcpipguide.com/free/t_RIPVersion2RIP2MessageFormatandFeatures-3.htm

RIP vs. RIP v2

VLSM = Variable Length Subnet mask Discontiguous == two connecting subnets come

from different classful network Such as connecting 172.16.16.1/24 with 10.3.1.1/24

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Discontiguous

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Interior Gateway Protocols (IGP) and Exterior Gateway Protocols (EGP)

IGP

EGP

Border Gateway Protocol (BGP).

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OSPF Protocol OSPF: the acronym for Open Shortest

Path First (EGP/IGP) Standardized in RFC 2328 Uses link-state routing Offers several advantages:

Updates routing tables more quickly when changes occur on the network

Balances the network load by splitting traffic between routes with equal metrics

Supports authentication of routing protocol messages

OSPF and RIPs

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How powerful/useful OSPF is

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IPv6 Routing

Cannot broadcast RIPng <== RIPv2 EIGRPv6 EIGPR OSPFv3 OSPF

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? --cast

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