Sybex CCNA 640-802 Chapter 7: EIGRP and OSPF. Chapter 7 Objectives Enhanced IGRP (EIGRP) –EIGRP...

Sybex CCNA 640-802Chapter 7: EIGRP and OSPF

• Enhanced IGRP (EIGRP)– EIGRP tables– Configuring EIGRP– Verifying EIGRP

• Open Shortest Path First (OSPF)– Configuring OSPF– Verifying OSPF– Configuring OSPF with wildcards

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• EIGRP is an advanced distance-vector routing protocol that relies on features commonly associated with link-state protocols.

• EIGRP uses Link State's partial updates and neighbor discovery.

• EIGRP's advanced features supports IP, IPX and AppleTalk.

• EIGRP uses RTP (Reliable Transport Protocol) to transport its routing updates

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4

EnhancedIGRP

IP RoutingProtocols

IPX RoutingProtocols

AppleTalk Routing Protocol

IP RoutingProtocols


• Enhanced IGRP supports:– Rapid convergence– Reduced bandwidth usage– Multiple network-layer support

• EIGRP includes support for AppleTalk, IP, and Novell NetWare as well as IP and IP v.6. The AppleTalk implementation redistributes routes learned from the Routing Table Maintenance Protocol (RTMP). The IP implementation redistributes routes learned from OSPF, RIP, IS-IS, EGP and BGP. The Novell implementation redistributes routes learned from Novell RIP or Service Advertisement Protocol (SAP).


• Enhanced IGRP supports:– Uses Diffused Update Algorithm (DUAL) to select

loop-free routes and enable fast convergence.• DUAL enables EIGRP routers to determine whether a path

advertised by a neighbor is looped or loop-free, and • Allows a router running EIGRP to find alternate paths

without waiting on updates from other routers.– Up to 6 unequal paths to remote network, default = 4

EnhancedIGRP



IP RoutingProtocols



IP RoutingProtocols

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• Both IGRP and EIGRP:– Use “Autonomous Systems” (AS) to divide the

internetwork • [This is the number that you include when configuring the

protocol; e.g.: “router (e)igrp 1”• All routers in the same AS

– use at least one common protocol, – share the same routing information and – are “contiguous”.

– They also use the same metrics: bandwidth, delay, load and reliability; with MTU as a tiebreaker.

– Same load balancing properties

– Maximum hop count of 255 (100 default)6

• But EIGRP:– Includes the subnet mask information in its routing

updates, which allows the use of VLSM.– And helps EIGRP to differentiate between internal

(within an AS) and external (between ASs) routes– Also, it does not send “any periodic updates” (which

IGRP sends every 90 seconds)– EIGRP has improved convergence time – much

faster than IGRP– EIGRP also sharply reduces network overhead

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• No updates: Route updates sent only when a change occurs – multicast on 224.0.0.10

• “Hello” messages sent to neighbors every 5 seconds (60 seconds in most WANs)

Enhanced IGRP

EIGRP EIGRP

hello

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• EIGRP and PDMs (Protocol-dependent modules ):– Supports IP (and through IP (v.4 & 6), IPX, OSPF, IS-IS,

RIP and RIP v.2, EGP (Exterior Gateway Protocol), and BGP (Border Gate Protocol), AppleTalk which gives you RTMP (Routing Table Maintenance Protocol), and Novell NetWare, supporting IPX, Novell RIP and SAP (Service Ad Protocol).

– EIGRP supports more protocols than any other routing protocol, (only IS-IS comes close), by using PDMs.

– Each PDM keeps it’s own set of routing tables.– PDMs are responsible for network layer protocol-

specific requirements. • The IP-EIGRP module, for example, is responsible for sending

and receiving EIGRP packets that are encapsulated in IP. 9

• EIGRP (other features):– Is “Classless”– Supports VLSM and CIDR.– Supports “discontiguous” networks &

“summarization”– Uses RTP (Reliable Transport Protocol) (see ff) for

communication – uses multicasts and unicasts for quick updates with receipts for tracking data.

– Uses the “DUAL” algorithm; unique and efficient.

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• EIGRP sends out five different types of packets—– hello, – update, – query, – reply, and – acknowledge (ACK)—

• that establish the initial adjacency between neighbors and to keep the topology and routing tables current.

• When troubleshooting an EIGRP network, network administrators must understand what EIGRP packets are used for and how they are exchanged.

• For example, if routers running EIGRP do not form neighbor relationships, those routers cannot exchange EIGRP updates with each other and cannot connect to services across the internetwork. 11

• The following terms are related to EIGRP:• Neighbor table (contains neighbors)

– EIGRP routers use hello packets to discover neighbors. – When a router discovers and forms an adjacency with a new

neighbor, it includes the neighbor's address and the interface through which it can be reached in an entry in the neighbor table.

– This table is comparable to the neighborship (adjacency) database used by link-state routing protocols.

– It serves the same purpose—ensuring bidirectional communication between each of the directly connected neighbors.

– EIGRP keeps a neighbor table for each network protocol supported; in other words, the following tables could exist: an IP neighbor table, an IPX and an AppleTalk neighbor table.

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• Topology table (contains updates re: all routes)– When the router dynamically discovers a new

neighbor, it sends an update about the routes it knows to its new neighbor and receives the same back.

– These updates populate the topology table. – The topology table contains all destinations advertised

by neighboring routers; • in other words, each router stores its neighbors' routing

tables in its EIGRP topology table. – If a neighbor is advertising a destination, it must be

using that route to forward packets; • this rule must be strictly followed by all distance vector

protocols. • An EIGRP router maintains a topology table for each network

protocol configured (IP, IPX, and AppleTalk). 13

• Advertised distance (AD) & feasible distance (FD) – DUAL uses distance information, known as a metric or

cost, to select efficient, loop-free paths. – The lowest-cost route is calculated by adding the cost

between the next-hop router and the destination—referred to as the advertised distance—to the cost between the local router and the next-hop router. The sum of these costs is referred to as the feasible distance.

• Successor– Is a neighboring router that has a least-cost path to a

destination (the lowest FD) that is guaranteed not to be part of a routing loop

– Successors are used for forwarding packets. – Multiple successors can exist if they have the same FD.

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• Routing table (contains only the best routes)– Holds the best routes to each destination and is

used for forwarding packets. – Successor routes are offered to the routing table. – If a router learns more than one route to exactly the

same destination from different routing sources, it uses the administrative distance to determine which route to keep in the routing table.

– By default, up to 4 routes to the same destination with the same metric can be added to the routing table (the table can hold up to 6 unequal cost paths).

– The router maintains one routing table for each network protocol configured. 15

• Feasible successor (FS) – Along with keeping least-cost paths, DUAL keeps

backup paths to each destination. – The next-hop router for a backup path is called the

“feasible successor”. – To qualify as a feasible successor, a next-hop router

must have an AD less than the FD of the current successor route

• in other words, a feasible successor is a neighbor that is closer to the destination, but it is not the least-cost path and, thus, is not used to forward data.

• Feasible successors are selected at the same time as successors but are kept only in the topology table.

• The topology table can maintain multiple feasible successors for a destination.

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– If the route via the successor becomes invalid (because of a topology change for example) or if a neighbor changes the metric, DUAL checks for feasible successors to the destination.

– If a feasible successor is found, DUAL uses it, thereby avoiding recomputing the route.

– If no suitable feasible successor exists, a recomputation must occur to determine the new successor.

– Although recomputation is not processor-intensive, it does affect convergence time, so it is advantageous to avoid unnecessary recomputations.

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• The composite metric is calculated with the following formula:

• By default, k1=k3=1 and k2=k4=k5=0. The default composite metric for EIGRP, adjusted for scaling factors, is as follows:

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• BWmin is in kbps and the sum of delays are in 10s of microseconds.

• Example• The bandwidth and delay for an Ethernet interface are 10

Mbps and 1ms, respectively.• The calculated EIGRP BW metric is as follows:

– 256 × 107/BW = 256 × 107/10,000, – = 256 x (10,000,000/10,000)– = 256 × 10,000– = 256000

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• EIGRP routers actively establish relationships with their neighbors, similar to what Link State routers do.

• EIGRP routers establish “adjacencies” with neighbor routers by using small hello packets.

• The Hello protocol uses a multicast address of 224.0.0.10, and all routers periodically send hellos.

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• On hearing hellos, the router creates a table of its neighbors.

• The continued receipt of these packets maintains the neighbor table

• To become a neighbor, the following 3 conditions must be met:1. The router must hear a hello packet or an ACK from a

neighbor.2. The AS number in the packet header must be the same as

that of the receiving router.3. The neighbor’s metric settings must be the same.

• Note:– Each Layer 3 protocol has its own neighbor table.

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By forming adjacencies, EIGRP routers do the following:– Dynamically learn of new routes that join their

network – Identify routers that become either unreachable or

inoperable – Rediscover routers that had previously been

unreachable

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• EIGRP updates are set only when necessary and are sent only to neighboring routers. There is no periodic update timer.

• EIGRP use hello packets to learn of neighboring routes.• The holdtime to maintain a neighbor adjacency is three

times the hello time.• For hello is not received with the holdtime, the

neighbor is removed from the table.

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Default Hello Intervals and Hold Time for EIGRP

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– Topics now considered in more detail:

• EIGRP relies on four fundamental concepts: 1. neighbor tables,

2. topology tables,

3. route states, and

4. route tagging.

• Each of these is summarized in the slides that follow.

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SRTT: “Smooth Round Trip timer”: Time for round trip to neighbor and back.RTO: “Retransmission Time Out”: Time EIGRP waits to send a packet from its retransmission queue to a neighbor.Q count - the number of EIGRP Packets that the software is waiting to send 29

• AD (Advertised distance) is the metric that is reported by the neighbor router(s).

• FD (Feasible Distance) – Feasible distance is the metric that is reported by neighbor router(s), plus the cost associated with the forwarding link from the local interface to the neighbor router(s). – When multiple paths exist, the “local FD” is the lowest-cost

metric to a remote network.

• Feasibility Condition – If the AD from a given neighbor is less than the locally calculated FD, that neighbor meets the criteria to become the feasible successor.

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• Successor - A successor is a neighboring router that is currently being used for packet forwarding; it provides the least-cost route to the destination and is not part of a routing loop

• Feasible successor - A feasible successor is a backup route. Feasible successors provide the next lowest-cost path without introducing routing loops. – Feasible successor routes can be used in case the existing

route fails. – Packets to the destination network are immediately

forwarded to the feasible successor, which at that point is promoted to the status of successor

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• Successor route is used by EIGRP to forward traffic to a destination

• A successor routes may be backed up by a feasible successor route

• Successor routes are stored in both the topology table and the routing table

Routing Table—IPDestination 1 Successor

Topology Table—IPDestination 1 SuccessorDestination 1 Feasible Successor

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• In the previous slide, EIGRP's composite metric is replaced by a link cost to simplify calculations.

• RTA's topology table includes a list of all routes advertised by neighbors.

• For each network, RTA keeps the real (computed) cost of getting to that network and also keeps the advertised cost (reported distance) from its neighbor.

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• RTY is the successor to network 24, by virtue of its lowest computed cost 31. This value is also the FD to Network 24.

• RTA follows a three-step process to select a feasible successor to become a successor for Network 24:– Determine which neighbors have a reported distance (RD)

(=AD) to Network 24 that is less than 31.– RTX's RD is 30 < 31, meet FC and is a feasible successor.– RTZ's RD is 220 > 31, not meet FC, and cannot be a FS.

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(a) Is the Destination Network

• In this example, (a) is the destination network, • From C’s point of view, if it goes to (a) via B,

the FD is 3 and the AD is 1. Others entries are computed in the same manner.

• Note in the example that router D does not have a feasible successor identified. The FD for router D to router A is 2 and the AD via router C is 3. Because the AD is larger than the FD, no feasible successor is placed in the topology table.

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• Router C has a feasible successor identified because the AD for the next hop router is less than the FD for the successor.

• How about router E?

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• In the context of routing protocols, convergence refers to the speed and ability of a group of internetworking devices running a specific routing protocol to agree on the topology of an internetwork after a change in that topology.

• DUAL results in EIGRP's exceptionally fast convergence. Why?

• The FS provides the capability to make an immediate switchover to a backup route!

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• The most important table in EIGRP is the neighbor table and relationships tracked in the neighbor table are the basis for all the EIGRP routing update and convergence activity.

• The neighbor table contains information about adjacent neighboring EIGRP routers.

• A neighbor table is used to support reliable, sequenced delivery of packets.

• An EIGRP router can maintain neighbor tables, one for each PDM running (e.gmultiple ., IP, IPX, and AppleTalk) routed protocols.

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• Hello packets assist in the discovery of EIGRP neighbors. – The packets are multicast to 224.0.0.10.

• An acknowledgment packet acknowledges the reception of an update packet. – An acknowledgment packet is a hello packet with no data.– Acknowledgment packets are sent to the unicast address of

the sender of the update packet.

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• Update packets contain the routing information of destinations. – Update packets are unicast to newly discovered neighbors;

otherwise, update packets are multicast to 224.0.0.10 when a link metric changes.

– Update packets are acknowledged to ensure reliable transmission.

• Query packets are sent to find feasible successors to a destination. – Query packets are always multicast.

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• Reply packets are sent to respond to query packets. – Reply packets provide a feasible successor to the

sender of the query.– Reply packets are unicast to the sender of the query

packet.

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• The neighbor table and topology table are held in ram and are maintained through the use of hello and update packets.

Enhanced IGRP

EIGRP EIGRP

hello

To see all feasible successor routes known to a router, use the “show ip eigrp topology” command

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• EIGRP uses a composite metric to pick the best path: bandwidth and delay of the line by default.

• EIGRP can load balance across six unequal cost paths to a remote network (4 by default)

IPX

19.2

T1

T1 T1

IPX

AppleTalk

IP

AppleTalk

IPA B

DC

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172.16.10.010.110.1.0192.168.0.0

TokenRing

AS=10

Router(config)#router eigrp 10Router(config-router)#network 10.0.0.0Router(config-router)#network 172.16.0.0

192.168.0.0

A C

B

Enable EIGRP

Assign networks

If you use the same AS number for EIGRP as IGRP, EIGRP will automatically redistribute IGRP into EIGRP

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Redistribution is translating one type of routing protocol into another.

Router D

Router B

Router A

Router C

EIGRP IGRP

IGRP and EIGRP translate automatically, as long as they are both using the same AS number. See another example - next slide:

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Assuming all default parameters, which route will RIP (v1 and v2) take, and which route(s) will IGRP and EIGRP take to get from Routers A to B?

T1 T1

100BaseT

100BaseT

10BaseT

56K

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Router A Router B

• Displays the neighbors discovered by IP Enhanced IGRP

• Displays the IP Enhanced IGRP topology table

• Displays current Enhanced IGRP entries in the routing table

• Displays the parameters and current state of the active routing protocol process

• Displays the number of IP Enhanced IGRP packets sent and received

show ip protocolsRouter#

show ip route eigrp Router#

show ip eigrp traffic Router#

show ip eigrp neighbors Router#

show ip eigrp topology Router#

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-D is for “DUAL”

-[90/2172] is the administrative distance and cost of the route. The “cost” of the route is a composite metric comprised from the bandwidth and delay of the line

P1R1#sh ip route[output cut]Gateway of last resort is not setD 192.168.30.0/24 [90/2172] via 192.168.20.2,00:04:36, Serial0/0C 192.168.10.0/24 is directly connected, FastEthernet0/0D 192.168.40.0/24 [90/2681] via 192.168.20.2,00:04:36, Serial0/0C 192.168.20.0/24 is directly connected, Serial0/0D 192.168.50.0/24 [90/2707] via 192.168.20.2,00:04:35, Serial0/0P1R1#

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• Large Network support:– Support for multiple Autonomous Systems: This is

one way to break up a large number of hosts.

• VLSM Support and Summarization:– Support for “discontiguous networks”:– This is a network in which 2 subnets of a classful

network; say, 10.1.0.0 and 10.2.0.0, which are both part of the “classful” 10.0.0.0 network,

– are separated by a different classful network; say 172.16.0.0, or any subnet in that network.

– By default, EIGRP does not handle this configuration, (only OSPF can), but it can be configured to do so. 59

• Load Balancing:– EIGRP can handle equal or unequal load balancing– By default, up to 4 links; up to 6 links can be

configured with the “maximum paths” command.

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• Initial Setup (pg 426, and Cisco command reference):• Step Command Purpose

• 1 router eigrp autonomous-system Enable an EIGRP routing process in global config mode.

• 2 network network-number Associate networks with an EIGRP routing process in router config mode.

• Create a Passive Interface This prohibits an interface from sending or

– Router(config-router)#passive-interface serial 0/1 receiving Hellos; so it will never form

adjacencies.

• Redistribution and Set Metric values– The following example takes redistributed Routing Information Protocol (RIP) metrics and translates

them into EIGRP metrics with values as follows: bandwidth = 1000, delay = 100, reliability = 250, loading = 100, and MTU = 1500.

– router eigrp 1– network 172.16.0.0 Command Syntax– redistribute rip redistribute (IP)– default-metric 1000 100 250 100 1500 default-metric bandwidth delay reliability loading mtu

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• Load Balancing –– This is automatic with EIGRP; the only time you need to configure

it is when you want to vary the load over each of several links.– In this case you would use the “traffice-share balanced” or the

“variance” command:• To control how traffic is distributed among routes when there are multiple

routes for the same destination network that have different costs, use the traffic-share balanced command in router configuration mode. To disable this function, use the no form of the command.

– traffic-share balanced

• To control load balancing in an Enhanced Interior Gateway Routing Protocol (EIGRP) based internetwork, use the variance command in router configuration mode. To reset the variance to the default value, use the no form of this command.

– variance multiplier 62

•Open standard•Shortest path first (SPF) algorithm•Link-state routing protocol (vs. distance vector)•Can be used to route between AS’s

• Consists of areas and autonomous systems• Minimizes routing update traffic• Supports VLSM• Unlimited hop count

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Link State:• Provides common view of entire topology• Calculates shortest path• Utilizes event-triggered updates• Can be used to route between AS’s

Distance Vector:•Exchanges routing tables with neighbors•Utilizes frequent periodic updates

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InternalRouters

Area 1 Area 2

ASBR andBackbone Router

Backbone/InternalRouters

ABR and BackboneRouter

Backbone Area 0ABR and BackboneRouter

InternalRouters

•External AS

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Feature RIP OSPFAlgorithm Vector-distance Link-state

Maximum Hops15 hops. 16 hops is considered to be infinity, implying that the destination is unreachable

Limited only by size of routing tables within routers

Subsystem Segmentation

Treats the autonomous system as a single subsystem

Breaks the autonomous system into one or more areas with two levels of routing algorithms, intra-area, and inter-area.

Metric Destination/hop Destination/cost/link identifier

IntegrityNo authentication in RIP-1, Authentication has been added to RIP-2

Supports Authentication. Several authentication algorithms are available ranging from simple password operations to more complex cryptographic algorithms.

Complexity Relatively Simple

More Complex. Several more PDUs and exchanges are defined in the protocol. Routing tables are large and include not only destinations, but also a tree representation of local network.

AcceptanceWidely Available, BSD routed supports RIP

Newer, published in RFCs

Route OptionsIdentifies a single route to a destination

Supports multiple routes to a single destination. Facilitates load-balancing traffic distribution

Types of RoutesHost, network. RIP-2 adds the ability to transfer subnetwork route entries

Host, network, and subnetwork routes

Router(config-router)#network address mask area <area-id>

Assigns networks to a specific OSPF area

Router(config)#router ospf <process-id>

Defines OSPF as the IP routing protocol.

Note: The process ID is locally significant and is needed to identify a unique instance of an OSPF database

hostname R3

router ospf 10

network 10.1.2.3 0.0.0.0 area 0

network 10.1.3.1 0.0.0.0 area 0

hostname R2

router ospf 20network 10.0.0.0 0.255.255.255 area 0

hostname R1

router ospf 30network 10.1.0.0 0.0.255.255 area 0network 10.5.5.0 0.0.0.0 area 0

R3

R2R1

10.1.2.0 10.1.1.0

10.5.5.0

Area 0

10.1.3.0

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Router#show ip ospf interface

Displays area-ID and adjacency information

Router#show ip protocols

Verifies that OSPF is configured

Router#show ip route

Displays all the routes learned by the router

Router#show ip ospf neighbor

Displays OSPF-neighbor information on a per-interface basis

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• OSPF uses hello packets to create adjacencies and maintain connectivity with neighbor routers

• OSPF uses the multicast address 224.0.0.5

Hello?224.0.0.5

•Hello packets provides dynamic neighbor discovery•Hello Packets maintains neighbor relationships•Hello packets and LSA’s from other routers help build & maintain the topological database

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Neighbor: – Two routers that have an interface on a common network– Usually discovered by hello’s but can also be configured administratively

Adjacency– Relationship formed between selected neighbors in which routing

information is exchanged. Not all neighbors are adjacent– Only Broadcast and Non-Broadcast network types have Designated

and Backup Designated Routers!!!Neighbors

Cost=6

ABR

BDR

DR

Non-DRAdjacencies

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Term Description

Link stateInformation is shared between directly connected routers. This information propagates throughout the network unchanged and is also used to create a shortest path first (SPF) tree.

Area A group of routers that share the same area ID. All OSPF routers require area assignments.

Autonomous system (AS) A network under a common network administration.

CostThe routing metric used by OSPF. Lower costs are always preferred. You can manually configure the cost with the ip ospf cost command. By default, the cost is calculated by using the formula cost = 10 8 / bandwidth.

Router IDEach OSPF router requires a unique router ID, which is the highest IP address configured on a Cisco router or the highest numbered loopback address. You can manually assign the router ID.

AdjacencyWhen two OSPF routers have exchanged information between each other and have the same topology table. An adjacency can have the following different states or exchange states:

1. Init state —When Hello packets have been sent and are awaiting a reply to establish two-way communication.2. Establish bi-directional (two-way) communication —Accomplished by the discovery of the Hello protocol routers and the election of a DR.3. Exstart —Two neighbor routers form a master/slave relationship and agree upon a starting sequence to be incremented to ensure LSAs are acknowledged.

4. Exchange state —Database Description (DD) packets continue to flow as the slave router acknowledges the master's packets. OSPF is operational because the routers can send and receive LSAs between each other. DD packets contain information, such as the router ID, area ID, checksum, if authentication is used, link-state type, and the advertising router. LSA packets contain information, such as router ID also but in addition include MTU sizes, DD sequence numbering, and any options.

5. Loading state —Link-state requests are sent to neighbors asking for recent advertisements that have not yet been discovered.

6. Full state —Neighbor routers are fully adjacent because their link-state databases are fully synchronized. Routing tables begin to be populated.

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Topology table Also called the link-state table. This table contains every link in the whole network.

Designated router (DR)This router is responsible for ensuring adjacencies between all neighbors on a multiaccess network (such as Ethernet). This ensures all routers do not need to maintain full adjacencies with each other.

The DR is selected based on the router priority. In a tie, the router with the highest router ID is selected.

Backup DR A backup router designed to perform the same functions in case the DR fails.

Link-state advertisement (LSA)

A packet that contains all relevant information regarding a router's links and the state of those links.

Priority Sets the router's priority so a DR or BDR can be correctly elected.

Router linksDescribe the state and cost of the router's interfaces to the area. Router links use LSA type 1.

Summary linksOriginated by area border routers (ABRs) and describe networks in the AS. Summary links use LSA types 3 and 4.

Network links Originated by DRs. Network links use LSA type 2.

External linksOriginated by autonomous system boundary routers (ASBRs) and describe external or default routes to the outside (that is, non- OSPF) devices for use with redistribution. External Links use the LSA type 5.

Area border router (ABR)Router located on the border of one or more OSPF areas that connects those areas to the backbone network.

Autonomous systemboundary router (ASBR)

ABR located between an OSPF autonomous system and a non-OSPF network.

Each router in OSPF needs to be uniquely identified to properly arrange them in the Neighbor tables.

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• OSPF sends Hellos which elect DRs and BDRs• Routers form adjacencies with DRs and BDRs in a multi-access

environment• The next slide covers loopback interfaces. The reason you would

configure a loopback (a logical interface) is to assign it the highest priority interface on the router, thus ensuring that it will become the DR.

• This avoids the router selecting a physical interface as DR, which is sometimes undesirable because physical interfaces can go up and down and sometimes fail to provide a stable routing environment.

Multicast Hellos are sent and compared

Router with Highest Priority is Elected as DR

Router with 2nd Highest Priority is Elected as BDR

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Router ID (RID): – Number by which the router is known to OSPF– Default: The highest IP address on an active interface at the

moment of OSPF process startup– Can be overridden by a loopback interface: Highest IP address

of any active loopback interface – also called a logical interface

What is the default OSPF interface priority?

Router# show ip ospf interface ethernet0/0Ethernet0 is up, line protocol is up

Internet Address 192.168.1.137/29, Area 4

Process ID 19, Router ID 192.168.1.137, Network Type BROADCAST,

Cost: 10 Transmit Delay is 1 sec, State DR, Priority 1

Designated Router (ID) 192.168.1.137, Interface address 192.168.1.137

No backup designated router on this network

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:06

Index 2/2, flood queue length 0

Next 0x0(0)/0x0(0)

Last flood scan length is 0, maximum is 0

Last flood scan time is 0 msec, maximum is 0 msec

Neighbor Count is 0, Adjacent neighbor count is 0

Suppress hello for 0 neighbor(s)

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ip ospf priority • To set the router priority, which helps determine the designated

router for this network, use the ip ospf priority command in interface configuration mode. – To return to the default value, use the no form of this command.

• ip ospf priority number-value • no ip ospf priority number-value

• Syntax Description– number-value <A number value that specifies the priority of

the router. The range is from 0 to 255>

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What options can you configure that will ensure that R2 will be the DR of the LAN segment?

If you want to advertise a partial octet (subnet), you need to use wildcards.– 0.0.0.0 means all octets match exactly– 0.0.0.255 means that the first three match exactly,

but the last octet can be any value

After that, you must remember your block sizes….

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The wildcard address is always one less than the block size….– 192.168.10.8/30 = 0.0.0.3– 192.168.10.48/28 = 0.0.0.15– 192.168.10.96/27 = 0.0.0.31– 192.168.10.128/26 = 0.0.0.63– What the author means is that where, in the first line, you’ve

borrowed 6 bits to get a /30 subnet mask, and this would give you 64 subnets with 4 hosts in each! The “4” is the “block size” that the author refers to. So, in the wildcard, the last number must be one less than 4, or “3”.

– Same thing in line 2: /28 means 4 bits borrowed; this gives you 16 subnets with 16 hosts in each. Block size is 16 and the wildcard is 16-1, or 15.

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• Lab_A• E0: 192.168.30.1/24• S0: 172.16.10.5/30

• Lab_B

• E0: 192.168.40.1/24

• S0: 192.168.10.10/30

• S1: 192.168.10.6/30

• Lab_C

• E0: 192.168.50.1/24

• S1: 172.16.10.9/30

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• Go through all the written and review questions• Go over the answers with the class

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Sybex CCNA 640-802 Chapter 7: EIGRP and OSPF. Chapter 7 Objectives Enhanced IGRP (EIGRP) –EIGRP...

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Transcript of Sybex CCNA 640-802 Chapter 7: EIGRP and OSPF. Chapter 7 Objectives Enhanced IGRP (EIGRP) –EIGRP...