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CN2668 Routers and Switches. Kemtis Kunanuraksapong MSIS with Distinction MCTS, MCDST, MCP, A+. Agenda. Chapter 8: Advanced Routing Protocols Exercise Quiz. Classful Routing Protocols. Summarize networks to their major network boundaries (Class A, B, or C)

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Cn2668 routers and switches

CN2668Routers and Switches

Kemtis Kunanuraksapong

MSIS with Distinction



  • Chapter 8: Advanced Routing Protocols

  • Exercise

  • Quiz

Classful routing protocols
ClassfulRouting Protocols

  • Summarize networks to their major network boundaries (Class A, B, or C)

    • Do not carry subnet mask information in their routing table updates

  • Cannot be used

    • Networks with discontiguous subnets

    • Networks using VLSM

  • Examples: RIPv1 and IGRP

Classful routing protocols cont
ClassfulRouting Protocols (Cont)

Classful routing protocols cont1
Classful Routing Protocols (Cont)

  • Figure 8-3 on Page 202 shows that RIP on RouterA is set to S0/0 and f0/0

  • In the same time, an update from RouterC to RouterBmake RouterB thought that there is load balancing as shown in Figure 8-5 on Page 203

  • Hence, the ping results are 50% as shown in Figure 8-6 on Page 204

Classless routing protocols
Classless Routing Protocols

  • Allow dynamic routing in discontiguous networks

  • Carry subnet mask information in the routing table updates

  • See Figure 8-7 on Page 204

  • Examples: RIPv2, EIGRP, OSPF, and BGP

Classless routing protocols1
Classless Routing Protocols

  • Version 2

    • To switchs RIP to version 2

  • No Auto-summary

    • To overrides default behavior of summarizing to major network boundaries

  • As shown in Figure 8-9 and 8-10 on Page 205

Routing information protocol version 2
Routing Information Protocol version 2

  • RIPv2 is a set of extensions to RIPv1

    • A distance-vector routing protocol

    • Supports a maximum of 15 hops

  • The major change is RIPv2’s ability to carry subnet mask information

    • RIPv2 multicasts its updates using the multicast address of

Ripv2 continue1
RIPv2 (Continue)

  • Cisco routers can be configured on a per-interface basis

    • See Figure 8-14 on Page 207

    • If the interface has not set to send/receive version 1, the packet will be drop

      • See Figure 8-15 on Page 208

Ripv2 continue2
RIPv2 (Continue)

  • To authenticate routing peers

    • Both ends has to use RIPv2

  • Configuring RIPv2 authentication requires the following steps:

    • Define a key chain

    • Define keys in the key chain

    • Enable authentication on the interface by specifying the key chain to be used

    • Enable either clear text or MD5 authentication

    • Manage the keys (optional key lifetimes)

Enhanced interior gateway routing protocol
Enhanced Interior Gateway Routing Protocol

  • Enhanced Interior Gateway Routing Protocol (EIGRP)

    • A Cisco proprietary classless protocol designed to overcome the limitations found in IGRP

    • Distance-vector routing protocol

  • Protocol Dependent Modules (PDMs)

    • Allow EIGRP to carry multiple routed protocols within their own native packet formats

Eigrp continued
EIGRP (Continued)

  • EIGRP uses nonperiodic, partial, and bounded routing table updates

    • Update only when there is changed

    • Update only what is changed

    • Update to only the party affected

Eigrp continued1
EIGRP (Continued)

  • EIGRP makes use of a composite metric comprised of six different factors:

    • Hops, Load, Bandwidth, Reliability, Delay, MTU

  • By default, the formula used for metric calculation in EIGRP is:

    Metric = [(K1*Bandwidth + (K2*Bandwidth)/(256-load) + K3*Delay)*K5/(reliability + K4)]*256

    • NOTE: K1 = 1, K2 = 0, K3 =1, K4 = 0, K5 =0

Eigrp components
EIGRP Components

  • Protocol Dependent Modules (PDM)

    • Allow EIGRP to support multiple Network layer routed protocols such as IP, IPX, and AppleTalk

  • Neighbor discovery and maintenance

    • Allow EIGRP to discover neighbors and keep track of their status

Eigrp components continued
EIGRP Components (Continued)

  • Reliable Transport Protocol (RTP)

    • Routing table updates are an example of an EIGRP packet type that uses reliable multicast via RTP

    • See Table 8-1 on Page 214 for types of packet

  • Diffusing Update Algorithm (DUAL)

    • Allows EIGRP to quickly recover from a link outage and route around network problems

Eigrp components continued1
EIGRP Components (Continued)

  • Key terms associated with DUAL

    • Successor

      • the best route to a destination

    • Feasible distance (FD)

      • the lowest metric to a destination

    • Reported distance (RD)

      • the distance a router advertises to a network

Eigrp components continued2
EIGRP Components (Continued)

  • Key terms associated with DUAL

    • Feasible successor

      • a backup route to the successor route

    • Feasibility condition

      • Used to ensure that a backup route does not contains a loop

    • Adjacency

      • A relationship formed between EIGRP neighbors

Eigrp components continued3
EIGRP Components (Continued)

  • Show ipeigrp topology all-links

    • To show the entire topology table as show in figure 8-25 on Page 217

    • If the status is P or Passive, that means everything is good

    • The status A or Active could cause from hardware errors or configuration errors

Eigrp configuration
EIGRP Configuration

  • EIGRP is classless, but it summarizes to classful network boundaries by default

    • The no auto-summary command turns off this default behavior

    • Router eigrp [process-id]

      • Process-id has to be same on two routers for them to share EIGRP routes

  • See Figure 8-26 on Page 218 on command summary

    • the bandwidth command to set the actual bandwidth on serial links to prevent auto selection

Eigrp configuration continued
EIGRP Configuration (Continued)

  • EIGRP supports optional authentication of routing peers

  • Configuring EIGRP authentication requires the following steps:

    • Define a key chain

    • Define keys in the key chain

    • Enable authentication on the interface by specifying the key chain to be used

    • Manage the keys (optional key lifetimes)

Open shortest path first
Open Shortest Path First

  • An open standards, link-state routing protocol that supports classless routing, VLSM, and authentication

  • Link-state routing protocols allow routers to share a common view of the entire network

    • Each router sends out link-state advertisements (LSAs) describing its attached links to all routers in an area

  • Each router needs to hold a topological database of the entire area

Ospf continued
OSPF (Continued)

  • OSPF is ideally suited for large networks

    • Uses a concept known as areas to bound link-state advertisements

  • An area is the portion of a network within which LSAs are contained

    • All OSPF routers configured with the same area identification will accept LSAs from one another

    • See Figure 8-29 on Page 221

Ospf concepts
OSPF Concepts

  • Link

    • A router’s interface

  • Link-state

    • The status of a link on a router

  • Area

    • Defines the confines within which LSAs are contained

  • Cost

    • The default metric for OSPF

Ospf concepts continued
OSPF Concepts (Continued)

  • Cost

    • Bandwidth [speed in Kb]

    • See Table 8-3 on Page 222 for default cost

  • Reference-bandwidth for OSPF is Fast Ethernet or 100 Mbps

    • Any link 100 Mbps or faster has a cost of 1

    • See Figure 8-30 on Page 222

    • If you change the reference-bandwidth, you have to change on all routers

Ospf concepts continued1
OSPF Concepts (Continued)

  • Adjacencies database

    • Contains information about all OSPF peers with which a router has successfully exchanged Hello packets

    • Hello-interval and dead-interval must match on all routers for them to form the neighbor table

  • Topological database

    • Holds the common view of the network formed from the link-state advertisements that are received

Ospf concepts continued2
OSPF Concepts (Continued)

  • Designated routers (DRs)

    • On broadcast, multiaccess networks, OSPF elects a DR, which acts as a central point for LSAs

    • On multiaccess networks such as Ethernet, OSPF elects a DR and establish adjacencies with the DR only

  • Backup designated routers (BDRs)

    • It takes over if the DR fails

  • Ospf concepts continued3
    OSPF Concepts (Continued)

    • The election occurs via Hello process

    • The id can be one of three things

      • Highest IP address configured on a loopback interface

      • Highest IP address on an active physical interface

      • ID Set using the ospf router-id [ipaddress]

    Ospf operation
    OSPF Operation

    • Steps

      • An OSPF router forms adjacencies with neighbors

      • A DR and BDR are elected in OSPF

      • Routers will flood their link-state advertisements and go through the process of selecting the best route to each network

    • OSPF uses Dijkstra’s Shortest Path First algorithmto find the best path

      • Each router sees itself as the central point from which a loop-free, best-cost path to each network is determined

    Single area ospf configuration1
    Single-Area OSPF Configuration

    • Require two key commands

      • Router ospf [process id]

      • Network command use a wildcard number

        • Network area 0

    • Default-information originate

      • Allows injection of a default route

      • Must run on a border router

        • RouterB in Figure 8-29 on Page 221

    Ospf authentication
    OSPF Authentication

    • OSPF provides authentication of routing table updates via several methods

      • No authentication (the default)

      • Authentication with passwords sent in clear text

      • Authentication using MD5 hashing of a shared secret key

    Ospf authentication continued
    OSPF Authentication (Continued)

    • To perform MD5 authentication of routing updates in OSPF, two steps must be completed:

      • Configuration of authentication keys on each OSPF interface

        • See Figure 8-39 on Page 228

      • Configuration of area authentication

        • See Figure 8-40 on Page 229

    Controlling route traffic
    Controlling Route Traffic

    • passive-interface command

      • An important entry-level command for controlling route traffic

      • Disrupts the function of EIGRP and OSPF

    • The command causes a router to listen only on the passive interface

      • Therefore, if used with EIGRP or OSPF, the router will not send Hellos out the interface

    • The result is a link that is seen as having no neighbors on it

      • Therefore, it will not be used to form adjacencies


    • Review Questions

    • Lab

      • 8.2 – 8.4