EIGRP Lecture 33

Lecture No 32

Lecture No 32

EIGRP (Enhanced Interior Gateway Routing Protocol)It also the Cisco Proprietary Routing Protocol and it is use by only the Cisco Routers other routers can not use this protocol.

EIGRP is Hybrid Routing Protocol

It is basically Distance Vector Routing Protocol but it has also the features of Link State Routing Protocols just like in OSPF that is why it is also called the Hybrid Routing Protocol.But strictly speaking it is the Distance Vector Routing Protocol.

Some Features of OSPF in EIGRP

1 Neighbors Discovery using Hello PacketsIn EIGRP the Routers also exchange the Hello Packets with their Neighboring routers and neighboring information saves in the Neighboring Tables.2 Exchanging of Routing Information

In EIGRP all the routers directly exchange the routing information with their neighboring routers and in this case it is not more complicated as in OSPF. There is no DR or BDR Selection etc.3 Topology TablesWhen the routing information exchange between the router it first of all Stores in the Topology Table. And

EIGRP topology table is quite different from the OSPF topology table because OSPF Topology Table contains the Link State Data Base, and in EIGRP Topology Tables there is Simply Routes Information.In EIGRP Topology Tables there is Routing Information of all the Possible Routes for any Destination.For example:

If there are 4 possible routes for the Destination in EIGRP Topology table there will be all 4 possible routes for this Destination

In the case of RIP and IGRP and OSPF there are only the Best Path Information in the routing tables but in EIGRP there are all the Possible Path Information in the topology table, and Router will select the best path and put it into the routing table.4 Successor Route

The best route in EIGRP which is selected from the topology table and become able to enter into the routing table is called Successor Route.

5 Feasible Successor Routes

The remaining routes in the topology tables will become the Feasible Successor Routes. Its purpose is that whenever any Successor Route is down then the any Feasible Successor route will fulfill its deficiency and it immediately becomes the Successor Route, until the Original Successor Route does not Up.

Note:

Due to this process of selection of Successor Route immediately EIGRP is the best Routing Protocol, because in the case of RIP and IGRP whenever any Link becomes down then all the routes send the routing update and set hold down timers and when the hold down timers expire the network converges and at last the second best path is selected and again the routing information exchange. In this case more time is consumed to convergence of the Network.Note:In the case of RIP there are two reasons due to which routers do not select the feasible successor

1 RIP only save the best path information there for it has no any route which become the feasible successor so the network should have to converge.

2 In RIP there is possibility of developing the routing Loops if router try to send the traffic from its neighboring router it may be possible the neighboring router has high metric than it and routing loop develop.

Conditions for the selection of Feasible Successor

Let us see this Non technical Topology

It is non technical example for understanding the process of the selection of Feasible Successor let from Router A to network 10.0.0.0 there are three possible routes available.

All Possible Routes

from Router A toMetricMetricMetricFeasible

DistanceAdvertise

Distance

B (( E (( 10.0.0.01050107060

C (( F (( 10.0.0.01010010120110

D ((G (( 10.0.0.01020010220210

Very Important Points

Question:

What is Feasible Distance (FD)? And why it is used in EIGRP?

Answer:

The distance form the Source Router to its Neighboring Router and Distance from Neighboring Router to the Destination is called the Feasible Distance and the selection of the Successor Route in EIGRP is done on the Basis of Lowest Feasible Distance.

Question:

What is the Advertise Distance (AD)? And why it is used in EIGRP?

Answer:

The distance of the Neighboring Router with the Destination is called Advertise Distance and the selection of the Feasible Successor is done on the basis of the Advertise Distance.

The Route in EIGRP will be the Feasible Successor which Advertise Distance is Less than the Feasible Distance.Let us change the Topology

All Possible Routes

from Router A toMetricMetricMetricFeasible

DistanceAdvertise

Distance

B (( E (( 10.0.0.01050107060

C (( F (( 10.0.0.070401011050

D ((G (( 10.0.0.0150601022070

Question:

What is Benefit of the Feasible Conditions in EIGRP?Answer:

By applying the Feasible Conditions the Feasible Successor Route is selected which immediately used as the Successor Route when ever Original Successor Route is down for any reason.

The Feasible Successor prevents the creation of the Routing Loops in the EIGRP Networks. Because if a Route has Advertise Distance less than the Feasible Distance of the Successor Route it means its traffic is not going through it so if the Successor Route send its traffic through the Feasible Successor Route then it is 100% sure it will not develop the Routing loop.Because the routing loops produced when ever a Link 1 (metric=10) is down and its traffic is send to the neighboring Link 2 (Metric=20) but it is possible if Link 2 was sending Traffic through Link 1 then Routing Loops are developed.

It is the most important feature of the EIGRP that is why it is more useful routing protocol for only Cisco Routers.Question:

What is the convergence time of Network if there is EIGRP Routing Protocol is running?

Answer:

EIGRP has convergence time in msec because if any link (Successor Route) is down it just took the routing information (Feasible Successor Routes) form the Topology Table and put into the Routing tables now this Feasible Successor will work as the Successor Route. Till the original route is not Up. If there is not any route which is able to work as the Feasible Successor then the convergence time will be more.Metric Calculation of IGRP and EIGRPThe method of calculation of the Metric of the IGRP and EIGRP is same we just have to calculate the IGRP metric and multiply it with 256 we will get EIGRP Metric.

As we know default metrics of IGRP are Bandwidth and Delay we can find out the Composite Metric by using following Formulae and add both Bandwidth and Delay.

107

IGRP (Metric/Bandwidth)=

Bandwidth (in KB)

Delay

IGRP (Metric/Delay) =

10

IGRP (Composite Metric) = IGRP (Bandwidth) + IGRP (Delay)

EIGRP (Composite Metric) =256xIGRP (Composite Metric)Let us suppose in the following Scenario there is EIGRP is running and we have to calculate the composite metric.

10.0.0.0

We consider only the Outgoing InterfacesLet us suppose that Traffic is going from Router A and its final Destination is 10.0.0.0 there are three Routers in the Route and we have to find the Composite Metric for this Route.

We will add Delay of all the Outgoing Interfaces and put it into the Formula (Note: the Default Delay for Serial Interface of the Router is 2000

Delay of all Routers Outgoing Interfaces ( 200 + 100 + 100 + 10 = 410

10

Now put it into the formula Delay =

Delay

10

Delay EIGRP =

=0.02439

410The Lowest Band width of the Outgoing interface in KB ( 64 KB

107Now put it into the formula of Bandwidth =

64 KB

100000000

Bandwidth EIGRP =

=1562500

64Adding EIGRP Bandwidth and Delay = 0.02439+1562500 = 1562500.2534Composite Metric of EIGRP (

256x1562523.2534 = 40000000006Let us configure EIGRP in the following Network

routerA>routerA>enable

routerA#

routerA#config terminal

routerA(config)#

routerA(config)#router eigrp 1

routerA(config-router)#

routerA(config-router)#network 1.0.0.0



routerA(config-router)#

routerA(config-router)#end

routerA#

routerA#telnet 1.1.1.2 . . . .

routerB#

routerB#config terminal

routerB(config)#

routerB(config)#router eigrp 1

routerB(cinfig-router)#

routerB(config-router)#network 1.0.0.0



routerB(config-router)#

routerB(config-router)#end

routerB#

routerB#telnet 2.1.1.2 . . . .

routerC#routerC#config terminal

routerC(config)#

routerC(config)#router eigrp 1

routerC(config-router)#

routerC(config-router)#network 2.0.0.0



routerC(config-router)#

routerC(config-router)#end

routerC#

routerC#telnet 3.1.1.2 . . . .

routerD#

routerD#configure terminal

routerD(config)#

routerD(config)#router eigrp 1

routerD(config-router)#routerD(config-router)#network 3.0.0.0

routerD(config-router)#network 4.0.0.0

routerD(config-router)#network 200.100.200.0

routerD(config-router)#

routerD(config-router)#end

routerD#

Let us see the Routing Tables (Successor Routes).If we type this command [show ip routes] we will see only the Successor Routes Best Routes.Router A

routerA#

routerA#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default Gateway of last resort is no setC1.0.0.0 is directly connected to serial 0 interface

C4.0.0.0 is directly connected to serial 1 interface

C200.100.50.0 is directly connected to Ethernet 0 interface

D200.100.100.0[100/56475] via 1.1.1.2

serial0 80:45:44D200.100.150.0[100/46656] via 1.1.1.2 serial0 85:42:42

200.100.150.0 [100/46656] via 4.1.1.1serial1 25:44:44D200.100.200.0[100/56412] via 4.1.1.2

serial1 55:44:23

D3.0.0.0

[100/65651] via 1.1.1.2

serial0 45:42:22

3.0.0.0

[110/65651] via 4.1.1.2

serial1 22:41:42D2.0.0.0

[100/56852] via 1.1.1.2

serial0 11:44:45

routerA#

Similarly we can see all the routing tables of all routers using command

Show IP Route in router Privileged Mode.

======================================================

Let us see the Topology Tables (Alternate Routes or Feasible Successor Routes).If we want to see Alternate Routes or Feasible Successor for the all destination we will see its Topology Table by using the following command [show ip topology]

Show ip eigrp neighborsA

D

Route No 2

Route No 1

C

B

10.0.0.0

E

B

10

50

10

100

F

C

A

10

G

D

200

10

From these possible three Routes for the traffic which is coming from the Router A it is the Successor Route because it has Lowest Feasible Distance (FD=70).

Now these are two routes from which the Feasible Successor is to be selected.

The Route will be Feasible Successor which has Less Advertised Distance (AD) than the Feasible Distance (FD) of the Successor Route, So both Routes are not Feasible Successor.

10.0.0.0

E

B

10

50

10

70

10

40

F

C

A

150

10

G

D

60

From these possible three Routes for the traffic which is coming from the Router A it is the Successor Route because it has Lowest Feasible Distance (FD=70).

Now these are two routes from which the Feasible Successor is to be selected.

The Route will be Feasible Successor which has Less Advertised Distance (AD) than the Feasible Distance (FD) of the Successor Route,

So (C(E(10.0.0.0) Routes is Feasible Successor, because its Advertise Distance (AD=50) is Less than the Feasible Distance of (FD=70) Successor Route.

Only put the Minimum Bandwidth in KB of the Outgoing Interface of the Router in Route in the following formula and calculate the IGRP Bandwidth which is the Metric of the IGRP.

Put the Sum of all the Delays of all the Outgoing Interfaces of the Routers in Route in the following formula and calculate the IGRP Delay which is the Metric of the IGRP.

Put the IGRP Bandwidth and IGRP Delay in the following formula and calculate the IGRP Composite Metric.

Multiply IGRP Composite Metric with 256 and we get the EIGRP Composite Metric.

Traffic /Packets

D

C

B

A

10

100

100

200

10 MB

64 KB

256 KB

128 MB

IP (200.100.200.25)

IP (200.100.50.26)

IP (200.100.50.11)

IP (200.100.50.12)

200.100.200.0

200.100.50.0

E0 (200.100.200.100)

E0 (200.100.50.100)

2.0.0.0

4.0.0.0

B

C

E0 (200.100.150.100)

S0 (3.1.1.1)

S0 (1.1.1.2)

S1 (4.1.1.1)

S1 (4.1.1.2)

S0 (3.1.1.2)

S0 (1.1.1.1)

1.0.0.0

3.0.0.0

S1 (2.1.1.1)

S1 (2.1.1.2)

E0 (200.100.100.100)

200.100.150.0

200.100.100.0

IP (200.100.100.65)

IP (200.100.100.66)

IP (200.100.150.80)

IP (200.100.150.81)

Autonomous System Number

A Network or Internet Under one Administrative Control is called an Autonomous System.

How many seconds before this UPDATE came

IGRP sends Routing Info. After every 90 sec by Default. [0-90]

To which interface we can enter

Next Hope IP Address

[AD/Metric]

As we know Administrative Distance of EIGRP ( 100

Default Metrics of IGRP are (1Band Width

(2Delay

But we will see the Composite Metric which is composition of (Band Width + Delay)

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EIGRP Lecture 33