CCNA – Cisco Certified Network Associates

Routing and Static Routes

By Roshan Chaudhary

Lecturer

Islington College

Routing• It is a process by which router transfer packets from one network to

another.

Types of Route

• Directly Connected Route

• Static Route

• Dynamic Route

Routing Table Principles:1. Every router makes its decision alone, based on the information it has

in its routing table.

Asymmetric Routing

• As router doesn't necessarily have the same information in routing

table, packets travelling the network in one direction, using one path,

might return via another path.

2. The fact that one router has certain information doesn't means other

router should have same.

3. Routing information about a path from one network to another

doesn't provide information about the return path.

Best Path and Metric• If there are multiple paths to reach the same destination network,

each path uses a different Router's exit interface to travel.

• The best path is selected by a routing protocol based on the value or

metric to determine the distance to reach a network.

Paths

R1-R3 : If hop count is used as metric

R1-R2-R3 : If bandwidth is used as metric

Equal Cost Load Balancing• When a router has multiple paths to a destination network and the

value of the metric is also same, this is called as an Equal Cost Metric.

• Here, the router performs Equal Cost Load Balancing.

Basic Commands Examining Router Interfaces#show interfaces

• - administratively down: means that the interface is currently in the

shutdown mode, or turned off.

• - line protocol is down: means that the interface is not receiving a

carrier signal from a switch or the hub.

#show ip interface brief: quickly verify about interface's status, IP

address and so forth.

#show controllers: verifies the DTE or DCE, the clock rate and so forth.

Cisco Discovery Protocol (CDP)• It is a powerful monitoring and troubleshooting tool which is used to

get information about directly connected Cisco devices.

• By default, each Cisco device sends periodic messages, which are

known as CDP advertisements, to directly connected Cisco devices.

CDP Verifying Command#show cdp neighbors

#show cdp neighbors detail

For each CDP neighbor, the following information is displayed:

• neighbor device ID

• local interface

• holdtime value, in sec

• neighbor device capability code

• neighbor hardware platform

• neighbor remote port ID

Disabling CDP• Disable cdp globally, for the entire device

router(config)#no cdp run

• Stop cdp advertisements on a particular interface

router(config-if)#no cdp enable

Configuring Static Routesrouter(config)# ip route <destintion network address> <subnet mask>

<next-hop ip address | exit interface>

• network address: destination network address to be added to the

routing table

• subnet mask: subnet mask of the destination network address. It can

be modified to summarize a group on networks

• next-hop ip address: commonly referred to as the next-hop router's IP

address

• exit interface: outgoing interface that would be used in forwarding

packets to the destination network

Verifying Static Routes

Configuring Default Static Routerouter(config)# ip route 0.0.0.0 0.0.0.0 <exit interface | next-hop ip

address>

• The 0.0.0.0 0.0.0.0 network address and mask is called a "quad-zero"

route

Default static routes are used when:

• No other routes in the routing table match the packet's destination IP

address. A common use is when connecting a company's edge router to

the ISP network.

• When a router has only one other router to which it is connected. This

condition is knows as a Stub Router.

Troubleshooting a Missing RouteNetworks are subject to many different forces that can cause their

status to change quite often:

• an interface fails.

• a service provider drops a connection.

• there is an over-saturation of links.

• an administrator enters a wrong configuration