Static RIP IGRP

Question 1

Biggest difference between classless and classful protocols

Answer 1

Classlesss can support subnets

Question 2

Distance vector protocol

Answer 2

Distance vector algorithms do not allow a router to know the exact topology of an internetwork.
Distance - how far vector -in which direction
Routers pass periodic copies of routing table to neighbor routers and accumulate distance vectors.
—Uses Bellman Ford Algorithm
— It needs to find out the shortest path from one network to other
-How to determine which path is best?
There are two Distance Vector Protocol, Both uses different metric
RIP – Hops
IGRP - Composite

Question 3

Distance vector -Rip

Answer 3

Rip uses only hop count

Question 4

Distance Vector - IGRP

Answer 4

IGRP uses bandwidth and delay as Metric

Question 5

Routing loops

Answer 5

If all routers in an internetwork do not have up-to-date, accurate information about the state of the internetwork, they might use incorrect routing information to make a routing decision.

The use of incorrect information might cause packets to take less-than-optimum paths or paths that return packets to routers that they have already visited.

Question 6

Defining a Maximum

Answer 6

Define a limit on the number of hops to prevent infinite loops.
• RIP permits a hop count of up to 15, so anything that requires 16 hops is deemed unreachable
• The maximum hop count will control how long it takes for a routing table entry to become invalid Defining a Maximum

Question 7

Split Horizon

Answer 7

Solution to the Routing Loop problem
It is never useful to send information about a route back in the direction from which the original information came
Had split horizon been used in our example, Router B would not have included
information about network 10.4.0.0 in its update to Router

Question 8

Route Poisoning

Answer 8

–Routers advertise the distance of routes that have gone down to infinity.
–Route Poisoning. Usually used in conjunction with split horizon
–Route poisoning involves explicitly poisoning a routing table entry for an unreachable network
–Once Router C learned that network 10.4.0.0 was unavailable it would have
immediately poisoned the route to that network by setting its hop count to the routing
protocol’s infinity value
–In the case of RIP, that would mean a hop count of 16.

Question 9

What we can use to override split horizon

Answer 9

Poison Reverse

Question 10

Triggered Updates

Answer 10

–The router sends updates when a change in its routing table occurs.
–New routing tables are sent to neighboring routers on a regular basis.
–RIP updates occur every 30 seconds
–However a triggered update is sent immediately in response to some change in the routing table.
–The router that detects a topology change immediately sends an update message to adjacent routers that, in turn, generate triggered updates notifying their adjacent neighbors of the change.
–Triggered updates, used in conjunction with route poisoning, ensure that all routers know of failed routes.

Question 11

Holddown timers

Answer 11

The router keeps an entry for the “possibly down state”
in the network, allowing time for other

Holddowns are a technique used to ensure that a route recently removed or changed is not reinstated by a routing table update from another route

Holddown prevents regular update messages from reinstating a route that is going up and down (called flapping)

Holddowns prevent routes from changing too rapidly by allowing time for either the downed route to come back up

Holddowns make a router wait a period of time before accepting an update for a network whose status or metric has recently changed

Question 12

RIP timers

Answer 12

• Route update timer Sets the interval (typically 30 seconds) between periodic routing updates

• Route invalid timer Determines the length of time (180 seconds) before a router determines that
a route has become invalid

• Holddown timer This sets the amount of time during which routing information is suppressed. This continues until either an update packet is received with a better metric or until the holddown timer expires. The default is 180 seconds

• Route flush timer Sets the time between a route becoming invalid and its removal from the routing table (240 seconds).

Question 13

RIP protocol( Routing Information Protocol)

Answer 13

–Distance-vector routing protocol.
–RIP sends the complete routing table out to all active interfaces every 30 seconds
– RIP only uses hop count to determine the best way to a remote network
–It has a maximum allowable hop count of 15
–AD is 120
–Bellman-ford algorithm
–Works well in small networks, but it’s inefficient on large networks

Question 14

Passive-Interface

Answer 14

Passive-interface command prevents RIP update broadcasts from being
sent out a defined interface, but same interface can still receive RIP updates

Passive-interface command depends upon the routing protocol

RIP router with a passive interface will still learn about the networks advertised by other routers

EIGRP, a passive-interface will neither send nor receive updates.

Question 15

debug ip rip command

Answer 15

do not use ,can block router cuzz of big memory usage

Question 16

IGRP

Answer 16

–It is a distance vector routing protocol.
–Routing updates are broadcast every 90 seconds.
–Bandwidth, load, delay and reliability are used to create a composite metric.

–The main difference between RIP and IGRP configuration is that when you
configure IGRP, you supply the autonomous system number. All routers must
use the same number in order to share routing table information.

Question 17

IGRP Timers

Answer 17

–Update timers these specify how frequently routing-update messages should be sent. The default is 90 seconds.

–Invalid timers These specify how long a router should wait before declaring a route invalid if it doesn’t receive a specific update about it. The default is 3*90 = 270.

–Holddown timers These specify the holddown period. The default is three times the update timer period plus 10 seconds. 280 seconds

–Flush timers These indicate how much time should pass before a route should be flushed from the routing table. The default is seven times the routing update period. If the update timer is 90 seconds by default, then 7 × 90 = 630 seconds elapse before a route will be flushed from the route table.