book

IP Routing

by Ravi Malhotra

January 2002

Beginner

238 pages

6h 20m

English

O'Reilly Media, Inc.

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Audience
What Is IP Routing?

Getting RIP Running
RIP UpdateRIP MetricProcessing RIP UpdatesSteady StateParallel PathsProcess SwitchingFast Switching
Speeding Up ConvergenceSplit horizonCounting to infinityTriggered updatesPoison reverseSetting timers
Routes to hosts
Getting IGRP Running
IGRP Autonomous System NumberIGRP MetricInterface bandwidth, delay, reliability, load, and MTUModifying interface bandwidth, delay, and MTUIGRP routing updatePath bandwidth, delay, reliability, load, and MTUIGRP composite metricModifying IGRP metricsProcessing IGRP updatesParallel PathsUnequal metric (cost) load balancingSteady State
Setting TimersDisabling IGRP Hold-Downs
Multiple Default Routes
Getting EIGRP Running
Neighbor RelationshipReliable Transport ProtocolDiffusing Update Algorithm (DUAL)Reported distanceFeasible distance and successorFeasibility condition and feasible successorLoop freedomTopology tableConvergence in DUAL -- local computationConvergence in DUAL -- diffusing computationProtocol-Dependent ModuleEIGRP Packet FormatInternal routesExternal routes
Automatic SummarizationManual Summarization
Verifying Neighbor RelationshipsStuck-in-ActiveIncrease active timerEIGRP Bandwidth on Low-Speed LinksNetwork LogsIOS Version Check, Bug ListsDebug Commands
Getting RIP-2 Running
RIP-1/RIP-2 Interworking
VLSMUse of Subnet ZeroClassless Inter-Domain Routing (CIDR)
Getting OSPF Running
Backbone AreaBackbone RouterArea or Regular AreaInternal RouterArea Border Router (ABR)Autonomous System Boundary Router (ASBR)Stub AreaTotally Stubby AreaNot So Stubby Area (NSSA)OSPF Topological DatabaseOSPF Route Types
Neighbor Discovery: The Hello ProtocolRouter IDArea IDChecksumAuthenticationNetwork maskHello-intervalOptionsRouter priorityRouter dead-intervalDesignated router (DR)Backup designated routerNeighbor router ID listDR/BDR ElectionInterface StateNeighbor RelationshipDatabase ExchangeRouter LSA (type 1)Network LSA (type 2)Summary LSA (type 3)ASBR summary LSA (type 4)External LSA (type 5)NSSA external LSA (type 7)Flooding of LSAs
Summarizing at the ABR (Inter-Area Summarization)Summarizing at the ASBR (or External Route Summarization)
Stub AreasTotally Stubby AreasNSSAs
OSPF HierarchyIP AddressingRouter IDDR/BDRBackbone AreaNumber of Routers in an AreaNumber of NeighborsRoute SummarizationVLSMStub AreasVirtual LinksOSPF Timers
OSPF Area IDsOSPF Does Not StartVerifying Neighbor RelationshipsRoute SummarizationOverloaded RoutersSPF OverrunUsing the LS DatabaseNetwork LogsDebug Commands
BackgroundAS TypesGluing AS to AS... Physical Connectivity in the InternetInternet Registries: IP Addresses and AS NumbersClassless Inter-Domain Routing (CIDR)Acquiring an IP AddressAcquiring an AS Number
Starting BGPNeighbor RelationshipBGP Message TypesOpenUpdateNotificationKeepaliveOriginating RoutesE-BGP Versus I-BGPSynchronizationThe BGP TableAttributesORIGIN (type code 1)AS-PATH (type code 2)NEXT-HOP (type code 3)MED (type code 4)WeightLOCAL-PREF (type code 5)Atomic Aggregate (type code 6)Aggregator (type code 7)CommunityPath Selection
Filtering by Prefix (Address/Mask) InformationFiltering by AS-PATH Information
Design AlternativesA Case Study
ServicesNetwork ArchitectureAddressing/RoutingOperationsPrice
Filter Routing InformationBlock All Updates on an InterfaceFilter the Routes Sent out in UpdatesFilter the Routes Received in UpdatesApply an Offset to a Routing Metric
How to RedistributeMany Pitfalls...... and a Couple of Strategies

Content preview from IP Routing

Getting BGP Running

Starting BGP on a router is similar to starting any other routing process, such as RIP or IGRP. The command to start BGP is:

router bgp AutonomousSystemNumber

where AutonomousSystemNumber is the AS number of the local router.

This is where the similarity with other routing protocols stops. When configured under BGP, the following network statement:

network IPAddress [mask A.B.C.D]

specifies the prefix to announce to BGP peers. Compare this with the configuration of IGPs, where the network-number statement has very different semantics: it specifies the attached networks on which to discover neighbors or peers.

Speaking of peers, there are no mechanisms in BGP-4 to automatically discover neighbors. BGP-4 requires that peers must be specified by IP address. The command to specify a peer is:

neighbor IPAddress remote-as AutonomousSystemNumber

where IPAddress specifies the peer with an AS number of AutonomousSystemNumber.

Let’s look at TraderMary’s configuration for its connection to ISP-A, as shown in Figure 7-3. Line 1 in the following code block starts BGP with a local AS number of 100. Line 3 specifies that the prefix 192.200.200.0/26 be announced to TrdrMary-1’s BGP peers. Line 4 specifies that the network number 30.0.0.0 be announced as well, with an 8-bit mask (the natural classful mask is used when a mask is not specified). Line 5 specifies that all static routes should also be announced. (There are two static routes known to TrdrMary-1, as shown in lines 7 and 8). ...