73 ip routing two types: direct and indirect. routing provides for efficient network topologies....

11

IP RoutingIP Routing

Two types: direct and indirect.

Routing provides for efficient network topologies.

Flat networks cannot scale.

Protocols used today are the same ones that were used back in the shared network environment.

Two types of protocols IGP and EGP. IGP provides for routing within a single AS EGP provides for routing between ASs

22

Direct RoutingDirect Routing

Network numbers must match for direct routing.

Different network numbers for indirect routing.

Remote nodes may use a combination of both direct and indirect routing.

Direct RoutingDirect Routing

Indirect RoutingIndirect RoutingStation D 140.2.1.1Station D 140.2.1.1

DirectDirectRoutingRouting Station AStation A

140.1.1.1140.1.1.1Station BStation B140.1.2.1140.1.2.1

Station CStation C140.1.3.1140.1.3.1

33

Indirect RoutingIndirect Routing

Occurs when the source and destination network or subnet do not match.

Source will ARP for a router and send the datagram to the router.

The router will either forward the packet directly to the destination or it will forward it to another router in the path to the destination.

Routers decrement the TTL field.

Routers forward the packet based on the IP address and not the MAC address.

44

A FlowchartA Flowchart

Header and checksum valid?

Decrement TTL;TTL >= 0?

If route is available, search for MACaddress in ARP

cache

Build new packet withMAC address and

route packet throughport found in routing

table.

Received ARP reply,insert MAC and IP

address intoARP table

NO

YES YES

YES

NO

NO

Packet ReceivedPacket Received

Route found?

Default route available?

Discard originalpacket

Send ICMPerror messageto originator

YES

NOMAC address

found?

Route Table lookup based on

destination address

Send ARP requestand wait for a

response

Received ARP

Reply?

YES

NO

NO

YES

55

Routing Protocols - Distance VectorRouting Protocols - Distance Vector134.4.0.0134.4.0.0

134.3.0.0134.3.0.0

1122

Network Metric Port Age134.4.0.0 1 1 xxx134.3.0.0 1 1 xxx134.5.0.0 2 2 xxx

134.5.0.0134.5.0.0

66

Updating Other Routers (Distance Updating Other Routers (Distance Vectors)Vectors) Upon initialization, each router reads its preconfigured IP address and metric (cost

in hops) of all its active ports.

Each router transmits a portion of its routing table (network ID, metric) to each “neighbor” router.

Each router uses the most recent updates from each neighbor.

Each router uses the update information to calculate its own “shortest path” (distance in hops) to a network.

Tables are updated only:

If the received information indicates a shorter path to the destination network.

If the received update information indicates a network is no longer reachable.

If a new network is found.

77

A Bigger UpdateA Bigger Update

Route HopRoute Hop

Router A

Router B

X 1Y 1Z 2

Z Y X

W

W 1X 1Y 2Z 3

Router CNetwork Hop Router PortNetwork Hop Router Port

WW 11 LocalLocal 22

XX 11 LocalLocal 11

YY 22 BB 11

ZZ 33 BB 11

Z 1Z 1Y 1Y 1Z 1Z 1Y 1Y 1

Route HopRoute HopRoute Hop

88

IP Routing TablesIP Routing Tables

Network NumberNetwork Number Next HopNext Hop HopsHops Learned fromLearned from PortPort

132.2.0.0132.2.0.0 DirectDirect 1 1 RIP RIP 11




132.2.0.0132.2.0.0

130.1.0.0130.1.0.0

133.3.0.0133.3.0.0 134.4.0.0134.4.0.0

2.22.2 3.33.3

3.43.44.54.5

1.11.1

Port IP addressPort IP address(i.e., 132.2.2.2)(i.e., 132.2.2.2)

Routing TableRouting Table

99

UDP HeaderUDP Header UDP DataUDP Data

The Routing Information Protocol The Routing Information Protocol (Version 1)(Version 1)

DADA SASA TFTF CRCCRCDataData

IP HeaderIP Header IP DataIP Data

RIP HeaderRIP Header RIP DataRIP Data

1010

RIP Operational TypesRIP Operational Types

RIP can operate in either ACTIVE or PASSIVE mode.

Active means that it builds routing tables and responds to RIP requests.

Passive means that it can build a routing table for its own use, but it does not respond to any RIP requests.

Most workstations (PCs) use a default gateway (i.e., router) and not a routing update protocol like RIP.

1111

RIP Field DescriptionsRIP Field Descriptions

0 31

Up to 25 entriesUp to 25 entries

DADA SASA TFTF CRCCRCUDP DataUDP Data

CommandCommand VersionVersion ReservedReserved

ReservedReservedFamily of Net 1Family of Net 1

Net 1 addressNet 1 address

Set to 0Set to 0

Set to 0Set to 0

Distance of network 1Distance of network 1

Family of Net 2Family of Net 2 ReservedReserved


Distance of network 2Distance of network 2

Set to 0Set to 0

Set to 0Set to 0

IP HdrIP Hdr UDP HdrUDP Hdr

1212

Default Router and GatewaysDefault Router and Gateways

129.1.1.1129.1.1.1

Default RouteDefault Route129.1.1.1129.1.1.1

130.1.1.1130.1.1.1 Default RouteDefault Route130.1.1.1130.1.1.1

Default RouteDefault Route0.0.0.00.0.0.0

129.1.1.2129.1.1.2

129.1.1.2129.1.1.2

1313

Disadvantages of the RIPv1 ProtocolDisadvantages of the RIPv1 Protocol

RIPv1 only understands the shortest route to a destination, based on a simple count of router hops.

It depends on other routers for computed routing updates.

Routing tables can get large and these are broadcasted every 30 seconds.

Distances are based on hops, not real costs (such as the speed of a link).

Patched with split horizon, poison reverse, hold-down timers, triggered updates. It continues to be a router-to-router configuration. One router is fully

dependent on the next router to implement the same options.

Fix one problem and others appear.

1414

Scaling with RIPScaling with RIP

Router A

Router B

Z Y X

W

Router C

Z 1Z 1Y 1Y 1Z 1Z 1Y 1Y 1

WW 22XX 11YY 11ZZ 11




Router A previously sent its table

1515

Routers and Subnet MasksRouters and Subnet Masks

150.1.1.0150.1.1.0255.255.255.0255.255.255.0

160.1.1.0160.1.1.0255.255.255.0255.255.255.0

150.1.3.0150.1.3.0255.255.255.0255.255.255.0

150.1.0.0150.1.0.0

160.1.0.0160.1.0.0 150.1.3.0150.1.3.0

1616

RIP FixesRIP Fixes

Split Horizon—Rule states that a router will not rebroadcast a learned route back over the interface from which the route was learned.

Hold-Down Timer—Rule states that when a router receives information about a network that is unreachable, the router must ignore all subsequent information about that network for a configurable amount of time.

Poisoned Reverse and triggered updates—Rule states a router is allowed to rebroadcast a learned route over the interface from which it learned it, but the metric is set to 16. A triggered update allows a router to broadcast its table when a network is found to be down.

1717

Split Horizon DemonstratedSplit Horizon Demonstrated

Router A

Router B

Z Y X

W

Router C

XX 11YY 11ZZ 22WW 22

XX 11YY 11WW 22

WW 11XX 11


ZZ 11YY 11

1818

RIP Version 2RIP Version 2

CommandCommand VersionVersion UnusedUnusedRoute TagRoute TagAddress Family IdentifierAddress Family Identifier

Net 1 addressNet 1 addressSubnet maskSubnet mask

Next-Hop IP AddressNext-Hop IP Address

MetricMetricAddress Family IdentifierAddress Family Identifier Route TagRoute Tag


MetricMetricNext HopNext Hop

Subnet maskSubnet mask

DADA SASA TFTF CRCCRCUDP DataUDP DataIP HdrIP Hdr UDP HdrUDP Hdr

1919

AuthenticationAuthentication

Command Version UnusedAuthentification TypeOxFFFF

PasswordPassword

Address Family Identifier Route TagNet 2 address

Next HopSubnet mask

PasswordPasswordPasswordPasswordPasswordPassword

Metric

00 3131

2020

Subnet Mask FieldSubnet Mask Field


PasswordPassword


Next HopSubnet mask


Metric

00 3131

2121

Route Tag and Next-Hop FieldsRoute Tag and Next-Hop Fields


PasswordPassword


Next HopSubnet mask


Metric

00 3131

2222

Multicast Support Multicast Support

RIPv2 uses the multicast address of 224.0.0.9 to multicast, does not broadcast its table.

MAC address of 01-00-5E-00-00-09. Details of this conversion are covered in RFC 1700 and the

multicast section of this book

RIPv1 uses a broadcast address in both the IP header and the MAC header.

IGMP is not used for this multicast support.

2323

RIPv2 Compatibility with RIPv1RIPv2 Compatibility with RIPv1

Configuration parameters on the router for: RIPv1 only – version 1 messages will be sent RIPv1 compatibility – RIP 2 messages as broadcast RIPv2 – Messages are multicast None – No RIP messages are sent

2424

Open Shortest Path First (OSPF, RFC Open Shortest Path First (OSPF, RFC 2178)2178) Shortest-path routes based on true metrics, not just a hop count.

Computes the routes only when triggered to or every 30 minutes (whichever is less).

Pairs a network address entry with a subnet mask.

Allows for routing across equal paths.

Supports ToS.

Permits the injection of external routes (other ASs).

Authenticates route exchanges.

Quick convergence.

Direct support for multicast in both the IP header and the MAC header.

2525

An OSPF NetworkAn OSPF Network

RouterRouter

RouterRouter

RouterRouter

PCPC PCPC

PCPC

PCPC

HostHost

RouterRouter

Other AutonomousOther AutonomousSystemsSystems Backbone Area 0.0.0.0Backbone Area 0.0.0.0

Area 1Area 1 Area 2Area 2

Area 5Area 5

Area 4Area 4

2626

A Routing Protocol ComparisonA Routing Protocol Comparison

Function/Feature RIPv1 RIPv2 OSPFStandard Number RFC 1058 RFC 1723 RFC 2178Link State Protocol No No YesLarge Range ofMetrics

Hop Count(16=Infinity)

Hop Count (16 =Infinity)

Yes, based on 1- 65535

Update Policy Route Table every 30sec

Route Table every 30sec

Link state changes orevery 30 minutes

Update address Broadcast Broadcast, Multicast MulticastDead Interval 300 secs total 300 seconds total Up to 300 seconds

total. Usually shorterSupportsauthentication

No Yes Yes

Convergence Time Variable based on(number of routers xdead interval)

Variable based on(number of routers xdead interval)

Media Delay + Dead Interval

Variable LengthSubnets

No Yes Yes

SupportsSupernetting

No Yes Yes

Type of Service (TOS) No No YesMultipath routing No No YesNetwork Diameter 15 hops 15 hops N/A but up to 65535Easy to use Yes Yes No

2727

OSPF OverviewOSPF Overview

Upon initialization, each router records information about all its interfaces. Each router builds a packet known as the Link State Advertisement (LSA).

Contains a listing of all recently seen routers and their cost LSAs are restricted to being forwarded only in the orginated area

Received LSAs are flooded to all other routers. Each router makes a copy of the most recently “seen” LSA

Each router has complete knowledge of the topology of the area to which it belongs.

Adjacencies are formed between a Designated Router (and Backup DR) and other routers on a network.

Shortest Path Trees are constructed after routers exchange their databases. Router algorithm only when changes occur (or every 30 minutes, whichever is

shorter).

2828

OSPF Media SupportOSPF Media Support

Broadcast - Networks such as Ethernet, Token Ring, and FDDI.

Non-broadcast Multiaccess (NBMA) - access that does not support broadcast but allows for multiple station access such as ATM, Frame Relay, and X.25.

Point-to-Point - Links that only have two network attachments, such as two routers connected by a serial line.

2929

Router TypesRouter Types

RouterRouter RouterRouter

PCPC PCPCPCPC

HostHost

Other AutonomousOther AutonomousSystemsSystems

Backbone Area 0.0.0.0Backbone Area 0.0.0.0Internal RouterInternal Router

Area 1Area 1 Area 2Area 2 Area 4Area 4

Autonomous SystemAutonomous SystemBorder RouterBorder Router

BackboneBackboneRouterRouter

DesignatedDesignatedRouterRouter

Internal RouterInternal Router

BackupBackupDRDR

Area 3Area 3

Area BorderArea BorderRouterRouter

3030

Router Names and Routing MethodsRouter Names and Routing Methods

Three types of routing in an OSPF network: Intra-Area routing - Routing within a single area Inter-Area routing - Routing within two areas of the same AS Inter-AS routing Routing between AS systems

3131

Message TypesMessage Types

OSPF routers communicate by sending Link State Advertisement (LSAs) to each other. Type 1 - Router Links Advertisement Type 2 - Network Links Advertisement Type 3 - Summary Links Advertisement Type 4 - AS Boundary Router Summary Link Advertisement Type 5 - AS External Link Advertisement Type 6 - Multicast Group Membership LSA

LSAs contain sequence numbers to detect old and duplicate LSAs.

3232

Metrics (Cost)Metrics (Cost)

Reference RFC 1253

Metric = 10n8 / interface speed

Examples: => 100 Mbps 1 10 Mbps 10 E1 48 T1 65 64 kbps 1562 19.2 kbps 5208 9.6 kbps 10416

3333

Generic Packet FormulaGeneric Packet Formula

DADA SASA TFTF CRCCRCIP DataIP DataIP Header IP Header Protocol ID 89Protocol ID 89

Version Type Packet Length

Router ID

Area ID

Checksum Authentication Type

Authentication

LSA Specific1 – Hello, 2 – DB Description, 3 – LS Request,

4 – LS Update, 5 – LS Ack

3434

The Hello ProtocolThe Hello Protocol

Routers send periodic Hello messages to each other. The packet contains:

The router’s selection of the DR and BDR Router’s priority used to determine the DR and BDR Configurable timers that include:

Hello Interval – To determine when you should hear from a neighbor

RouterDeadInterval – The period before a router is declared down A list of neighbors the router has heard from

This can be turned off by setting the network to an NBMA. This is useful when there is only one router on the cable segment

AA BB CC DDBackupBackupDRDR

DesignatedDesignatedRouterRouter

CC BB 3030 1515 CC BB 8989 AA MCMC

3535

AdjacencyAdjacency

Hello

Hello DR = RT2

D-D Seq = x M, Master

D-D Seq = y M, Master

D-D Seq = y M, Slave

D-D Seq = y+1 M, Master

D-D Seq = y+1 M, Slave

D-D Seq = y+n, Master

D-D Seq = y+n, SlaveLS RequestLS UpdateLS RequestLS UpdateLS AckLS Ack

Down

ExStart

Exchange

Loading

Full

Down

ExStart

Exchange

Loading

Full

Router 1Router 1 Router 2Router 2Designated RouterDesignated Router

3636

Maintaining the DatabaseMaintaining the Database

After Dykstra runs, the database is checked for consistency.

Uses the flooding procedure: Receive an LSA Check for the information in the database Determine whether or not to forward this LSA to an adjacency

Reliability checked using an acknowledgment procedure.

Each LSA contains an age entry.

Sequence numbers are generated for every LSA.

3737

OSPF AreasOSPF AreasAS 1AS 1

Area 0Area 0




Could be a RIPCould be a RIPnetwork within the network within the same domain as OSPFsame domain as OSPF

Area 1Area 1 Internal Internal RouterRouterArea 2Area 2

ASBRASBR

Area Area BorderBorderRouterRouter

3838

The Backbone AreaThe Backbone Area

There must be at least one area in an OSPF network. It is called the backbone area.

Designated by area ID of 0.0.0.0.

Primarily responsibility to propagate information between areas.

Has the same attributes as any other area.

Any network topology may make up the backbone.

It can be used as a real network with attachments.

3939

The Area Border Router (ABR)The Area Border Router (ABR)

Connects an area (or areas) to the backbone.

Summarizes its area topology to the backbone.

Propagates summarized information from the backbone into its area.

Final router that receives an area’s LSA. ABRs do not flood LSA information into the backbone Only produces summaries to the backbone for the backbone to propagate to

other areas

Uses the network summary LSA.

Summarized information is propagated in an area by the DR and its adjacencies.

4040

Virtual LinkVirtual Link

ABRABR ABRABR

Virtual LinkVirtual Link

Area 2.2.2.2Area 2.2.2.2 Area 1.1.1.1Area 1.1.1.1 Backbone AreaBackbone Area

4141

Inter-Area RoutingInter-Area Routing

Area 1Area 1Area 2Area 2

Area BorderRouter

AS 1AS 1

Area 0Area 0

BackboneRouter

BackboneRouter

BackboneRouter

Could be a RIPnetwork within the same domain as OSPF

ASBR

4242

Information from other Autonomous Information from other Autonomous SystemsSystems

Uses the ASBR.

Other ASs according to OSPF may simply be a RIP network within the same OSPF domain.

External LSA used.

Type 1 – The preferred route and used when considering the internal cost of the AS.

Type 2 – Advertising the same metric as was advertised by the ASBR.

These are used to calculate the shortest path to the ASBR.

4343

Stub AreasStub Areas

An area that has only one entry and one exit point (must be the same area).

Used to reduce the number of external advertisements.

A stub area blocks AS external link advertisements.

Area 1Area 1 Area 2Area 2

Area 0Area 0

AS 2AS 2

Contains AS2Contains AS2route entriesroute entries

Does not Does not contain AS2contain AS2route entriesroute entries

4444

RFCs Related to OSPFRFCs Related to OSPF

2178 DS: J. Moy, “OSPF Version 2,” 07/22/97 (211 pages) (.txt format) (obsoletes RFC 1583).

2154 ES: M. Murphy, B. Badger, A. Wellington, “OSPF with Digital Signatures,” 06/16/97 (29 pages) (.txt format).

1850 DS: F. Baker, R. Coltun, “OSPF Version 2 Management Information Base,” 11/03/95. (80 pages)

(.txt format) (Obsoletes RFC 1253).

1793 PS: J. Moy, “Extending OSPF to Support Demand Circuits,” 04/19/95 (31 pages) (.txt format).

1765 E: J. Moy, “OSPF Database Overflow,” 03/02/95 (9 pages) (.txt format).

1745 PS: K. Varadhan, S. Hares, Y. Rekhter, “BGP4/IDRP for IP—OSPF Interaction,” 12/27/94 (19 pages) .txt format).

1587 PS: R. Coltun, V. Fuller, “The OSPF NSSA Option,” 03/24/94 (17 pages) (.txt format).

1586 I: O. deSouza, M. Rodrigues, “Guidelines for Running OSPF Over Frame Relay Networks,”

03/24/94 (6 pages) (.txt format).

1585 I: J. Moy, “MOSPF: Analysis and Experience,” 03/24/94 (13 pages) (.txt format).

1584 PS: J. Moy, “Multicast Extensions to OSPF,” 03/24/94 (102 pages) (.txt, .ps formats).

1403 PS: K. Varadhan, “BGP OSPF Interaction,” 01/14/93 (17 pages) (.txt format) (obsoletes RFC 1364).

1370 PS: Internet Architecture Board, “Applicability Statement for OSPF,” 10/23/92 (2 pages) (.txt format).

4545

Static versus Dynamic RoutingStatic versus Dynamic Routing Entries in a routing table can be static (manually entered by the network administrator) or

dynamic (learned through a routing protocol such as RIP).

Static entries: In the workstation for either:

Default Gateway (router) - used by indirect routing Place a static route in for one that is not learned through RIP, etc.

In the router: Entered as 0.0.0.0 and the next hop (no subnet) to indicate a default route Routers can broadcast this information to their networks to let everyone know which is

the default router A default router is one that all other look to for networks that are not in their tables

Static routes can be used to increase security on the network Any IP network address can be manually entered into the routing table The router administrator supplies:

IP Network address Subnet mask Next hop interface (the IP address of the next routers interface to get to the

network)

4646

Remote NetworksRemote Networks

T3T3T3T3

AAZZ

T1T1CaliforniaCalifornia

VirginiaVirginia

TexasTexas

T1T1 == 1.544Mbps1.544MbpsT3T3 == 45Mbps45Mbps

4747

Datagram RoutingDatagram Routing

PCPC

Host - 129.1.1.1Host - 129.1.1.1

RouterRouter

AA

BB

CC

DDEE

Host - 129.1.1.2Host - 129.1.1.2

129.1.1.3129.1.1.3

129.2.1.1129.2.1.1

129.2.1.2129.2.1.2

CC DD 08000800 129.2.1.2129.2.1.2 129.1.1.2129.1.1.2 IP DataIP Data CRCCRC

BB AA 08000800 129.2.1.2129.2.1.2 129.1.1.2129.1.1.2 IP DataIP Data CRCCRC

DADA SA SA TF TF Data Data CRCCRC

IP IP HeaderHeader

IP IP HeaderHeader

73 ip routing two types: direct and indirect. routing provides for efficient network topologies....

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