CN2668 Routers and Switches

thoughtlessskytopNetworking and Communications

Oct 29, 2013 (3 years and 8 months ago)

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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)


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
203


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

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 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 224.0.0.9

RIPv2 (Continue)


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 (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
(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 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
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 (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
summary


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
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 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


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)


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
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 (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 172.20.0.0 0.0.255.255 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)


Assignment


Review Questions


Lab


8.2


8.4