Chapter 8

Routers and Switches
Kemtis Kunanuraksapong
MSIS with Distinction
• Chapter 8: Advanced Routing Protocols
• Exercise
• Quiz
Classful Routing 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)
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
RouterB make RouterB thought that there is
load balancing as shown in Figure 8-5 on Page
• Hence, the ping results are 50% as shown in
Figure 8-6 on Page 204
Classless Routing Protocols
• Allow dynamic routing in discontiguous
• Carry subnet mask information in the routing
table updates
• See Figure 8-7 on Page 204
• Examples: RIPv2, EIGRP, OSPF, and BGP
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
• 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 (Continue)
RIPv2 (Continue)
• Cisco routers can be configured on a perinterface 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 (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
• Enhanced Interior Gateway Routing Protocol
▫ 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 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 (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
• 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)
• Reliable Transport Protocol (RTP)
▫ Routing table updates are an example of an
EIGRP packet type that uses reliable multicast via
▫ 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 (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 (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 (Continued)
• Show ip eigrp 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 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
▫ the bandwidth command to set the actual
bandwidth on serial links to prevent auto selection
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
• An open standards, link-state routing protocol
that supports classless routing, VLSM, and
• 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 is ideally suited for large networks
▫ Uses a concept known as areas to bound link-state
• 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
• Link
▫ A router’s interface
• Link-state
▫ The status of a link on a router
• Area
▫ Defines the confines within which LSAs are
• Cost
▫ The default metric for OSPF
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 (Continued)
• Adjacencies database
▫ Contains information about all OSPF peers with
which a router has successfully exchanged Hello
▫ 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
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 (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
• 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
algorithm to 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 Configuration
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 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)
• 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
• 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
Controlling Route Traffic (continued)
• Review Questions
• Lab
▫ 8.2 – 8.4
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