• advanced distance vector
• 100% loop free
• Fast convergence
• Partial updates
• multiple network-layer support
• multicast & unicast
• VLSM support
• seamless connectivity across all data-link layer protocols and topologies
• Sophisticated metric
• load balancing across equal and unequal-cost pathways
• easy LAN and WAN configuration
• manual summarization at any point
• flexible network design

• Neighbor discovery and recovery mechanism
• Reliable transport protocol
• DUAL
• Protocol-dependant modules

• Diffusing Update Algorithm
• enables RIGRP routers to find out whether a path to the destination network is loop-free.  DUAL allows a router running EIGRP to find alternate paths based on updates received from other routers.

• Neighbor table
• Topology table
• Routing table

1. Hello
2. Update
3. Query
4. Reply
5. ACK

• The list of all routes learned from each EIGRP neighbor
• The source for the topology table: IP EIGRP Neighbor Table

• The list of all best routes from the EIGRP topology table and other routing processes
• The source for the EIGRP routes in an IP routing table: IP EIGRP Topology table

• The cost or state of a directly connected link changes
• An EIGRP packet (update, query, reply) is received
• A neighbor is lost

1. Bandwidth (K1)
2. Loading (K2)
3. Delay (K3)
4. Reliability (K4 & 5)

1. Verify and configure IP addressing
2. Enable EIGRP using the correct AS number
3. Define networks to include per router
4. Define a special metric to influence path selection

1. Topology
2. AS numbering and IP addressing
3. Netoworks included in EIGRP per routers
4. Non-default metric applied

1. Define the network requirements
2. Gather the required parameters
3. Define EIGRP routing
4. Configure basic EIGRP
5. Verify EIGRP configuration

1. EIGRP routing protocol AS number
2. Interfaces for EIGRP neighbor relationship
3. Networks participating in EIGRP
4. Interface bandwidth

1. Define EIGRP as a routing protocol
2. Define the attached networks participating in EIGRP
3. Define the interface bandwidth

How should the bandwidth command be used for:

1. Generic serial interfaces like PPP and HDLC
2. Frame relay on p-to-p interfaces
3. Frame relay on multipoint connections
4. PVCs with different CIRs

1. line speed
2. CIR
3. sum of all CIRs
4. lowest CIR multiplied by by number of PVCs on multipoint connection

• 90 - AD, administrative distance
• 40514560 - Metric

What is the relationship between between

• The EIGRP metric for a certain network
• The FD for that network in the topology table

What is the relationship between

• The next-hop address in the EIGRP routing table
• The successor in the EIGRP topology table

1. Prevents a neighbor relationship from being established over the passive interface
2. Stops routing updates from being received or sent over the passive interface
3. Allows a subnet on the passive interface to be announced in an EIGRP process

• 16 max
• 4 default

• Variance is the degree to which EIGRP performs unqual-cost paths
• Variance is only a multiplier, not a max-path parameter

• The route must be loop free.  AD < total distance, or when route is feasible successor.
• The metric of the route < the metric of the best route (successor), multiplied by the variance configured on the router.

1. Improves network stability
2. Reduces resource utilization
3. Simplifies remote router (spoke) configuration

• K1 = 1
• K2 = 0
• K3 = 1
• K4 = 0
• K5 = 0

1. AS number
2. Authentication type, keystring & ID
3. Metric K values

• 224.0.0.5 OSPF routers
• 224.0.0.6 OSPF DR

• Neighbor
• Topology
• Routing

Describe the link state neigbor table in OSPF

x3

• aka adjacency database
• lists immediately connected routers
• stores adjacency information

Describe the link-state topology table for OSPF

x3

• aka link state database (LSDB)
• information on all routers in an area
• LSDB is identical for all routers in the same area

• Each router independantly calculates the best path using Dijkstra's algorithm.
• Overcomes "routing by rumors" limitation of distance vector

• two levels
• area 0 (backbone), and normal areas (non-backbone)

What is the Cisco recommended max number of routers per OSPF area

• ABR - Area Border Router
• ASBR - Autonomous System Border Router
• Internal Router
• Backbone Router

• non-backbone, normal area router
• all interfaces in one area

Internal router in area 0

• connects area 0 to normal areas
• has interfaces in more than one area

• connects any OSPF area to a different routing protocol
• the point where external routes can be redistributed into OSPF

• Separates LSA flooding zones
• Becomes primary point for area address summerization
• Functions regularly as the source for default routes
• Maintains LSDB for each area it is connected to.

• routers find the best path by applying Dijkstra's algorithm to the LSDB
• the best path is based on lowest total cost and placed in the routing table

• also called "cost"
• defined per interface, but may be altered
• inversely proportional to the bandwith of that interface
• COST = 100,000,000 / bandwidth [b/s]

1. Hello protocol is used to define neighbors
2. Adjacency is established
3. Adjacent routers exchange LSAs
4. Each router builds an LSDB using LSAs

• Area ID
• Authentication (password)
• Hello and Dead intervals
• Stub area flag

True or False:

OSPF adjacent routers have the exact same link-state database

What are the OSPF router states of adjacency

x8

1. Down
2. Attempt
3. INIT
4. Two-way
5. Exstart
6. Exchange
7. Loading
8. Full

• adds entry to LSDB
• sends link-state ACK back
• floods info to other routers
• runs SPF
• updates its routing table

• adds entry to LSDB
• sends link-state ACK back
• floods info to other routers
• runs SPF
• updates its routing table

• higher sequence number
• higher checksum number
• age equal to max age (poisoning)
• significantly smaller link-state age (LSA is significantly younger)

What is the OSPF implementaion plan

x5

1. Verify and configure IP addressing
2. Enable OSPF for the correct interfaces
3. Enable OSPF for the correct areas
4. Define special metric to influence path selection
5. Verify the configuration

What should be included in OSPF documentation

x5

1. Topology
2. Areas and IP addressing
3. Networks and interfaces included in OSPF per router
4. Default and non-default metrics applied
5. Configuration and verification results

• encapsulated directly into an IP payload
• protocol ID of 89 in IP header
• does not use TCP or UDP
• uses its own ack routine using the ack packet type (OSPF packet type 5)

• Hello
• Database description (DBD)
• Link-state request (LSR)
• Link-state update (LSU)
• Link-state Acknowledgement (LSAck)

• Discovers neighbors and builds adjacencies between them
• Contains list of known neighbors

• Checks for database synchronization between routers
• Contains a summary of the LSDB

• Requests specific link-state records from another router
• contains the type of LSU needed and the router ID that has the needed LSU

• sends specifically requested link-state records
• contains the full LSA entries.  Multiple LSAs can fit in one LSU

• Acknowledges the other packet types
• packet is empty

What is contained in an OSPF hello packet

x8

• router ID
• Hello and Dead intervals
• neighbors
• Area ID
• Router priority
• DR and BDR IP addresses
• Auth password
• Stub area flag

• This is bidirectional communication with a neighbor
• At the end of this stage the DR and BDR election would have been done
• The routers must decide whether to proceed in building adjacency or not
• The decision is based on whether one of the routers is a DR or BDR, or the link is ptp or virtual.

• routers are finalizing the information exchange

• LSA options field has changed
• age of the LSA instance is MaxAge
• length field in the LSA header has changed
• the contents of the LSA have changed

• Does not require DR or BDR
• auto detected by OSPF
• sends OSPF packets on 224.0.0.5

• reduces routing update traffic
• manages link-state sync

• Hello packets exchanged
• router with highest OSPF priority is DR
• second highest is BDR
• OSPF router ID used as tie breaker
• non-preemptive

What are the five OSPF network types for NBMA

(see p 3-58)

• broadcast
• non-broadcast
• point-to-multipoint
• point-to-multipoint non-broadcast
• point-to-point

• highest IP address on an active interface at moment of OSPF process startup
• highest IP address on a loopback interface.  Loopback trumps regular interface

What are the OSPF LSA Types

(see p 3-99)

• 1- Router LSAs
• 2- Network LSAs
• 3 or 4- Summary LSAs
• 5- AS external LSAs
• 6- Multicast OSPF LSAs
• 7- LSAs defined for NSS areas
• 8- External attribute LSAs for BGP
• 9,10,11- Opaque LSAs

1. Backbone
2. Normal
3. Stub
4. Totaly Stubby
5. Not So Stubby

1. O: Networks from within the area of the router, advertised by means of router LSA and network LSA
2. O IA: Networks from outside the area of the router, but within the OSPF autonomous system, advertised by summary LSA
3. O E1: Networks outside the AS of the router, advertised by external LSA
4. O E2: "

• E1 route add external cost to the internal cost.  Use when there are multiple ASBRs to prevent suboptimal routing.
• E2 uses external cost only.  Use if only 1 ASBR.  This is the default

What command configures OSPF route summarization at an ABR

(config-router)# area 0 range ip netmask

On an ASBR:

(config-router)# summary-address ip netmask

(config-router)# default-information originate (metric #)

accepts link updates, route summaries, and external routes

All areas connect here to exchange routing info

Includes all properties of a standard area

• Only accepts Summary and Default routes
• Does not accept info about routes from external AS
• Routers use default routes to get outside the AS
• Stub areas cannot contain ASBRs

• Only accepts default routes
• Does not accept external AS routes
• does not accept summary routes within the AS
• Uses a default route
• cannot contain an ASBR

• defines special LSA type 7
• same as stub or totally stubby area
• Allows ASBRs

1. area has a single exit point, or a default route is used with multiple exit points
2. all routers in the area must be configured as stub routers before becoming neighbors
3. no ASBR in area
4. area is not backbone
5. area not needed for virtual link transit

(config-router)# area 2 stub no-summary

required on ABR ONLY

• External E1 E2 routes
• summerized routes IA

(config-router)# area 2 nssa

ON ALL ROUTERS IN THE AREA

(config-router)# area 2 nssa no-summary

on ABR ONLY

NSSA default route

(config-router)# area 1 nssa default-information-originate

• Router with highest OSPF priority
• Tie-breaker is the highest OSPF router ID

• Neighbors must be manually configured
• DR and BDR election required

• routers auto identify neighbors
• Do NOT elect DR and BDR

1. Router

2. Network

3. Summary

4: ASBR Summary

5: External

7: NSSA External

• Router LSA
• One LSA for each router in an area
• contains link states of the router

• Network LSA
• One LSA for each area
• Sent by the DR
• Contains all the routers in an area

• Summary LSA
• Sent be the ABR of the originating area
• advertises any networks owned by an area to all other areas in the OSPF AS
• Flooded in single area only, regenerated by ABR's to flood into other areas

Describe a Type 4 LSA

• ASBR Summary LSA
• Generated by an ABR only when there is an ASBR in the area
• Identifies ASBR and provides a route to it.

• External LSA
• Describes routes to networks outside the OSPF AS
• Flooded throughout the entire AS

• NSSA External LSA
• Describes routes to networks outside the OSPF AS
• Only exists in an NSSA area
• converted to type 5 LSA by first ABR

• RIP and RIPv2
• EIGRP and OSPF do not accept updates on passive interfaces

• bandwidth K1
• Loading K2
• Delay K3
• Reliability K4 + 5

• MED
• prefered path INTO an AS
• shared between AS's
• Local Preference
• preferred path OUT of AS
• only shared within AS

• show ip ospf interface
• show ip ospf neighbor

show ip ospf database

(database-summary)

• access-list y permit ip host 0.0.0.0 host 0.0.0.0
• access-list 100 permit ip any host 0.0.0.0
• access-list x permit 0.0.0.0