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CCNA 3 v3. 1 Module 2

CCNA 3 v3. 1 Module 2. CCNA 3 Module 2. Single Area OSPF. Distance Vector Routing. RIPv1, RIPv2, IGRP, EIGRP Interior gateway routing protocol Sends copies of routing tables to neighbors View network from neighbors perspective Updates at specified times (30 secs,90 secs)

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CCNA 3 v3. 1 Module 2

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  1. CCNA 3 v3.1 Module 2

  2. CCNA 3 Module 2 Single Area OSPF

  3. Distance Vector Routing • RIPv1, RIPv2, IGRP, EIGRP • Interior gateway routing protocol • Sends copies of routing tables to neighbors • View network from neighbors perspective • Updates at specified times (30 secs,90 secs) • Slow convergence • High bandwidth usage

  4. Link State Protocols • Examples • OSPF (Open Shortest Path First) • IS-IS(Intermediate System to Intermediate System • Also known as Shortest Path First (SPF) • Dijkstra algorithm calculates loop free topology • Interior gateway protocol • Sends routing updates to all routers within the autonomous systems • All routers have a complete view of the network topology • Routers maintain a complex database of the topology • Link state database is identical on all routers • Routers have full knowledge of distant routers and how they interconnect • Require more memory and processing

  5. Triggered updates • Contain changes only • Occur when topology change occurs • Updates sent to all routers • Triggered updates result in • Fast convergence • Efficient use of bandwidth • OSPF configuration • OSPF routing process must be enabled • Networks must be identified

  6. Link State Protocol • Send triggered updates • when a network change has occurred • periodic updates known as link-state refreshes • Each router keeps track of • the state or condition of its directly connected neighbors by multicasting hello packets • all the routers in its network using link-state advertisements (LSAs) • Builds database about the network using • hello information and LSAs • Calculates shortest route to each network using • shortest path first (SPF) algorithm • Stores this route information in its routing table

  7. Topological Database • Every router advertises directly connected networks • via Link State Advertisements • Every router has it’s own view of the network • it builds a ‘topological database’ • Router A is aware of 2 paths to 192.168.157.0 • this provides redundancy should one of the routers fail

  8. Advantages of Link State Protocols • Use cost metrics to choose paths • Cost metric reflects the capacity of the links • Fast convergence because • Triggers flooded updates • No routing loops - router knows network topology • Routing decision based on up to date of information • LSAs are sequenced and aged • Minimised Link-state database sizes • because of Dijkstra calculations and faster convergence • Supports • Classless interdomain routing (CIDR) • Variable-length subnet masking (VLSM)

  9. Disadvantages of LSP • More memory and processing power required • In particular during initial setup • Require strict hierarchical network design • to reduce the size of the topology tables • Administrator must have a good understanding of link-state routing • Flooding of LSAs during the initial discovery process • decrease network transport capability • Uses the available bandwidth

  10. Compare Distance Vector and Link State

  11. OSPF • Non-Proprietary protocol • Preferred to RIP because it is scalable • Open Standard - IETF RFC 2328 • Link State routing protocol • Interior Gateway Protocol for Autonomous systems • Metric based on bandwidth • Supports VLSM • OSFP can use ‘areas’ for hierarchical design • Multiple areas connect to a distribution area, area 0, also called the backbone

  12. OSPF Terminology • Link • an interface on the router • Link State • Status of a link • Relationship to neighbouring router • Flooding • sends information out all ports, except the port the information was received • Link State Database – topological database • List of information about all other routers • Shows the internetwork topology

  13. Area A collection of networks and routers Each router in the area has the same link-state information A router within an area is an internal router Area 0 - Backbone Cost Based on bandwidth Transmission speed Routing table Generated when SPF algorithm is run on link-state dbase Unique to each router

  14. Adjacent database List of all directly connected routers Designated Router (DR) / Backup Designated Router (BDR) a router elected by all others to represent the network area All LSA sent to DR/BDR instead of to every single router Multicast address 224.0.0.6 Reduces overhead of LSA updates Standard on multi-access networks DR is single point of failure – solution is BDR

  15. OSPF Network Types • Multi-access • Number of routers is unknown • Info sent to DR and BDR • Point-to-Point • 2 routers • DR and BDR not elected • NBMA • Info sent to DR and BDR

  16. OSPF Hello Protocol • Hello protocol sends hello packets at • Router starts up • To initiate new adjacency • Regular intervals • ensure neighbor still functioning • Every 10 seconds on broadcast multi-access and point-to-point networks • Every 30 seconds to NBMA such as frame relay • Hello packets have a L3 multicast address • 224.0.0.5 - This address is all OSPF routers • Hello packet has OSPF packet header • with a type field of 1

  17. Configuring OSPF • Only 1 area • Number is 0 • Multiple areas • Number between 0 to 65,535 • Must connect to area 0 • Router(config)#router ospf process-id (1 to 65,535) • Router(config-router)#network network-address wildcard-mask area-id • Router(config)#router ospf 1 • Router(config-router)#network 10.2.1.2 0.0.0.0 area 0

  18. Configure OSPF loopback address • OSPF must have an active interface at all times • Not always possible if ethernet / serial interface are down • Create a loopback interface (logical interface) to overcome this • OSPF uses the loopback interface address as the router ID (this overrides local IP address values) • If there is more than one loopback interface • highest loopback IP address is taken as router ID • Loopback configuration Commands • router(config)#interface loopback number • Router(config-if)#ip addressip-address subnet-mask • Subnet mask is always 255.255.255.255 • To turn off a loopback address • Router(config)#nointerface loopback number

  19. Setting OSPF Priority Priorities can be set from 0 to 255 0 prevents that router from being elected Highest OSPF priority will win the election for DR Configuring OSPF priority • Router(config)#interface fa0/0 • Router(config-if)#ip ospf priority 50 • Router(config0if)#end

  20. OSPF Cost Metric • OSPF uses Cost metric for path selection • Cost is based on bandwidth • Default bandwidth is 1.544Mbps – cost is 64 • Cost can be 1 (100Mbps) to 65535 • Cost is 108÷ bandwidth • Configuration • Router(config)#interface serial 0/0 • Router(config-if)#bandwidth 64 • Router(config-if)#ip ospf costnumber

  21. OSPF Authentication • To guarantee trust OSPF uses authenticatication • Authentication key shared between routers • password can be up to eight characters • Router(config-if)#ip ospf authentication-keypassword • After password is configured, enable authentication • Router(config-router)#areaarea-numberauthentication • This is sent in plain text – easy to decode • To send encrypted authentication • Router(config-if)#ip ospf message-digest-keykey-idmd5encryption-type key • MD5 keyword is the message-digest hashing algorithm to use • Encryption type is the type of encryption • where 0 means none and 7 means proprietary. • key-id 1 through 255 • key is an alphanumeric password up to sixteen characters • Neighbor routers must use the same key identifier with the same key value • Router(config-router)#areaarea-idauthentication message-digest

  22. OSPF Default Route • Used to reach networks outside the domain • gateway of last resort • Command • Router(config)#ip route 0.0.0.0 0.0.0.0 [interface | next-hop address] • referred to as the quad-zero route

  23. What Causes a failure to establish a neighbor relationship • Hellos are not sent from both neighbors. • Hello and dead interval timers are not the same. • Interfaces are on different network types. • Authentication passwords or keys are different. • Other possibilities • All interfaces haven’t correct addresses or subnet mask • network area statements hasn’t correct wildcard masks • network area statements interfaces not in correct area

  24. Verifying OSPF • Show ip protocol • Displays, times, filters, metrics, networks • Show ip route • Displays routes known and how they were learned • Show ip ospf interfaces • Verifies interfaces configured in an area • Show ip ospf • Displays how many times SPF has been executed • Show ip ospf neighbor details • Displays a list of neighbors, priorities and states • Show ip ospf database • Displays the contents of the topological database

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