How to Configure Interior Gateway Routing Protocol (IGRP)?Interior Gateway Routing Protocol (IGRP) is a distance-vector ro...
from the routing table. The default is seven times the routing update timer       which is equal to 630 seconds.Configurin...
Notice that we use the same AS number (100) in order for the two routers to be ableto exchange IGRP routing protocol updat...
Use the show interface command to view the metrics used on the specific interfaceon which IGRP is being routed.IGRP uses t...
The IGRP ScenarioIf IGRP has lower AD than RIP, then I should use IGRP, right?Actually the answer is NO. There is no singl...
Upcoming SlideShare
Loading in …5
×

How to configure interior gateway routing protocol

583 views
482 views

Published on

How to configure interior gateway routing protocol

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
583
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
17
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

How to configure interior gateway routing protocol

  1. 1. How to Configure Interior Gateway Routing Protocol (IGRP)?Interior Gateway Routing Protocol (IGRP) is a distance-vector routing protocol. It isalso a Cisco proprietary routing protocol – which means that all routers in yournetwork must be Cisco routers in order to run IGRP.Before getting into all the details of IGRP take a quick look aton Dynamic RoutingProtocols for some detailed information on distance-vector routing protocols. Thiswill help you understand the limitations and problems of distance-vector routingprotocols and the necessity of an enhanced routing protocol like IGRP. The maximumhop count of 15 in RIP is enhanced into a maximum hop count of 255 with a defaultof 100 in IGRP – making IGRP more appropriate for larger networks.Moreover IGRP uses a composite metric to determine the best route to aninternetwork. It’s called a composite because it uses a combination of metrics –bandwidth and delay of the link by default. Reliability and load of the link can also beused as metrics.Later on we’ll take a look at how these metrics are combined to form a compositemetric.Main Characteristics of IGRP IGRP is a Cisco proprietary distance vector routing protocol. IGRP sends routing updates every 90 seconds, advertising networks of a particular autonomous system. By default IGRP uses bandwidth and delay as metrics. It can be configured to use a combination of variables such as bandwidth, delay, load and reliability to establish a composite metric. IGRP has an administrative distance of 100 making it a more trustworthy routing protocol than RIP which has an administrative distance of 120.IGRP Timers Update timer: specifies how frequently routing update messages should be sent. The default is 90 seconds. Invalid timer: specifies how long a router should wait in the absence of routing-update messages about a specific route before declaring that route invalid (or unreachable). The default is three times the update period which is equal to 270 seconds. After this period, the route is placed in the holddown state. Holddown timer: specifies the amount of time a router should wait after expiration of the invalid timer. During this time the specific route is marked as unreachable and information about alternative routes is ignored. The IGRP default for this variable is three times the update timer period plus 10 seconds = 280 seconds. Flush timer: indicates how much time should pass before a route is flushedhttp://blog.router-switch.com/
  2. 2. from the routing table. The default is seven times the routing update timer which is equal to 630 seconds.Configuring IGRPConfiguring IGRP is similar to configuring RIP. The only difference is that you have touse anAutonomous System (AS) number in order to be able to turn on IGRP. Thesame AS number needs to be configured on all IGRP enabled routers on the networkin order to be able to exchange routing updates. A router may use more than one ASnumber. This way it can share different pieces of information with different routers.Let’s use the following subnet internetwork to configure IGRP routing:The router igrp command turns IGRP routing on in the router. The AutonomousSystem number specified here is 100 (it can be any number between 1 and 65535).Notice that IGRP uses classful routing, similar to RIP, meaning that it does not sendsubnet mask information along with the routing protocol updates.http://blog.router-switch.com/
  3. 3. Notice that we use the same AS number (100) in order for the two routers to be ableto exchange IGRP routing protocol updates.Verifying IGRPIssuing the command show ip route on routerA you can notice that routinginformation for network 172.16.0.0 has been acquired via IGRP. The I means IGRPlearned routes. The 100 in [100/80135] is the administrative distance of IGRP and80135 is the composite metric. The lower this metric, the better the route.Using the command show ip protocols you can verify IGRPs operation. Informationregarding IGRP timers, AS number and maximum hop count can be obtained fromthis command. Moreover the metric variables can be seen here as well (K1- K5).Metric Calculationhttp://blog.router-switch.com/
  4. 4. Use the show interface command to view the metrics used on the specific interfaceon which IGRP is being routed.IGRP uses the following metric calculation:Metric=[K1* bandwidth + (K2 * bandwidth)/(256-load) + (K3 * delay)]*[K5/(reliability +K4)]By default only bandwidth and delay are considered in the metric calculation. Toobtain this behavior (seen on the show ip protocols command as well) the followingdefault variable values are configured:K1=1, K2=0, K3=1, K4=0, K5=0, whereK1 is for bandwidth, K2 for load, K3 for delay, K4 and K5 for ReliabilitySubstituting the default values in the metric calculation we end up with:Metric= bandwidth + delayThe values used in the metric calculation are not the raw values obtained fromthe show interface command. Actually these raw values are used in the followingequations to compute the calculated values which are displayed in the show iproute command: Bandwidth = (10000000/raw bandwidth measured in Kb/s) Delay = (raw delay in s/10)Example: For a serial interface with a bandwidth of 1544 kb/s and delay of20000X10-6 s the calculated values used in IGRP routing updates would be: Bandwidth = 10000000/1544 = 6476 Delay = 20000/10 = 2000To end up with the final composite metric, the router sums up all calculated delaymetrics on the outgoing interfaces along the route towards a given destination andthe Bandwidth calculated metric taken from the lowest bandwidth along the route.http://blog.router-switch.com/
  5. 5. The IGRP ScenarioIf IGRP has lower AD than RIP, then I should use IGRP, right?Actually the answer is NO. There is no single best case solution. There is no bestsolution among RIP and IGRP.Networks vary in many ways. You need to fully understand the operation of theserouting protocols and try to adapt their operation into the architecture of yournetwork in order to differentiate their pros and cons.Though I cannot tell you which of these two protocols is better, what I am able to tellyou is that if you do have the option to use EIGRP, then you should use it over IGRPor RIP. EIGRP is definitely a better routing protocol than both RIP and IGRP.More Networking Tips:Static Routing vs. Dynamic RoutingHow to Troubleshoot OSPF?How to Configure EIGRP on a Cisco Router?http://blog.router-switch.com/

×