Network Simulation With OPNET Modeler

• M.KAMRAN USMANI

ABSTRACT

Routing protocol is the key for the quality of modern communication network. EIGRP, OSPF and RIP are the dynamic routing protocols being used in the practical networks to propagate network topology information to the neighboring routers. There have been a large number of static and dynamic routing protocols available but choice of the right protocol for routing is dependent on many parameters critical being network convergence time, scalability, memory and CPU requirements, security and bandwidth requirement etc.

This Assignment uses OPNET simulation tool to analyze the performance of RIP and EIGRP commonly used in IP network.

Initially We have Following Network.

By Examining the Network we figure out that Red line indicating the Data Rate of 44.736 Mbps between network components and only Network connection between London Office and Portsmouth office has Data Rate of 64 Kbps.

The Traffic Flow between London Office and Bristol_corporate is IP_Traffic Flow having following chracteristics   

RIP Protocol Over Netwrok:

Routing Information Protocol (RIP) is a distance vector dynamic routing protocol that employs the hop count as a routing metric. RIP is implemented on top of the User Datagram Protocol (UDP) as its transport protocol. It is assigned the reserved port number 520. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination. The maximum number of permitted hops is 15. Hence a hop count of 16 is considered an infinite distance. This hop number limits the size of networks that RIP may support. RIP selects paths that have the smallest hop counts. However, the path may be the slowest in the network. RIP is simple and efficient in small networks.

First we have to run RIP routing protocol in the network for a simulation period of 600 seconds with selecting following criteria

1. Path Selection
2. Time Taken for routing convergence
3. Protocol Overhead

Path Selection

For path selection we get following result with RIP protocol

The IP traffic Flow is from London to Bristol Corporate and due to Low Data rate between London to Portsmouth path as compare to London to Oxford path the RIP protocol follows maximum the low Data rate path which is London Office to Portsmouth, and graph displays data throughput for the links London to Portsmouth and Portsmouth to Bristol.

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Time Taken for routing convergence

RIP is distance vector routing protocols, announces its routes in an unsynchronized and unacknowledged manner. This can lead to convergence problems. The graph is showing the time taken for routing convergence of RIP. The convergence time is high 6.975 sec that’s mean routers are finding it difficult to exchange state information.

Protocol Overhead

RIP is a “distance vector” based protocol selects the best routing path based on a distance metric

(the distance) and an interface (the vector) , RIP protocols evaluate the best path based on

distance, which can be measured in terms of hops or a combination of metrics calculated to represent a distance value. In this exercise RIP selects London to Portsmouth link and maximum utilization occurs .

The utilisation and convergence data suggests there is some queuing and blocking on the link. For example, the utilisation for the London to Portsmouth link is high i.e 84.629 therefore suggesting the link is suffering from over-utilisation.

Queuing/Delay

In the point to point queuing graph , the London to Portsmouth Link contains queuing delay on average 3.6032 sec , therefore suggesting there is traffic blocking or queuing on the link.

The link between London to Portsmouth uses a DS0 (Blue) cable with a data rate of 64Kbps compared to the other links in the network that use a DS3 cable (Red) with a data rate of 44.736Mbps; therefore the combination of the over-utilisation of the London to Portsmouth link with the low data rate cable (DS0) has caused traffic queuing or blocking to occur.

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EIGRP Protocol Over Netwrok:

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary routing protocol. It is based on a new route calculation algorithm called the Diffusing Update Algorithm (DUAL). It has features of both distance vector and link state protocols. EIGRP metrics are based on reliability, MTU, delay, load, and bandwidth. Delay and bandwidth are the

basic parameters for calculating metrics

First we have to run EIGRP routing protocol in the network for a simulation period of 600 seconds with selecting following criteria

1. Path Selection
2. Time Taken for routing convergence
3. Protocol Overhead

Path Selection

For path selection we get following result with EIGRP protocol

The IP traffic Flow is from London to Bristol Corporate but as contrast with RIP which selected low data rate path, EIGRP select the path from London to Oxford , Oxford to Birmingham , and Birmingham to Bristol path to achieve the traffic Flow.

Time Taken for routing convergence

EIGRP is more efficient as compared to RIP , Graphs are showing the convergence duration very fast 0.0074427 Sec as Compared to RIP which was 6.975 Sec with same scenario.

Protocol Overhead

As Compared to RIP , No over utilisation occurs in EIGRP , Utilisation graphs shown above clearly that the utilisation distributed evenly over path with value for the London to Oxford is 5.5606 , Oxford to Birmingham is 5.5783 and Birmingham to Bristol is 5.5662

EIGRP performs better in terms of network convergence, routing traffic, and Ethernet delay.

EIGRP has the characteristics of both distance vector and link state protocols, has improved network convergence, reduced routing protocol traffic, and less CPU and RAM utilization compared to RIP protocol.

EIGRP has very low usage of network resources during normal operation since only hello packets are transmitted. When a routing table changes, its convergence time is short and it reduces bandwidth utilization

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FAILURE SCENARIO

We introduced a link Failure Scenario between Bristol corporate and Porstmouth Office after 100 Seconds and its recovery at 200 Seconds and run the RIP and EIGRP protocol over network.

Following are our Observations with side by side comparison of RIP and EIGRP

Utilization

In the RIP protocol the link failure after 100 sec prevented the traffic to flow; therefore when the link recovered after 200 sec a huge amount of traffic was bottlenecked on the link causing the utilisation of the London to Portsmouth to suddenly increase. Also it can be observed that during the time of the failure the RIP protocol began to reroute the traffic over the London to Oxford, Oxford to Birmingham, and Birmingham to Bristol links before the link recovered the graph is showing this small utilization on the links.

In the EIGRP Protocol, link failure event did not affect the utilisation of the EIGRP protocol because the link was not used in the routing path; The EIGRP did not use the link Portsmouth to Bristol in its path selection, so the performance of the network will be barely affected by the failure ; hence the utilisation values doesn’t change

Convergence

In RIP The Convergence Duration becomes much higher as compare to old scenario before Failure , it was 6.975 before and 19.409 now , this is because routers updates their routing tables when failure occurred and recovered it takes more time period ,

In Contrast with EIGRP protocol the Convergence Duration becomes 0.012273 , much less than RIP this is because EIGRP only update the link failure routing table not the whole network , So EIGRP provides much efficient and faster way to achieve convergence.

Time Delay of Protocol

More IP packets drops in RIP as compared to EIGRP because of the failure in link of the path which RIP follows , and as contrast less IP packets drops in EIGRP because it does not follow the path of failure link.

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Consider the given Network merging with another network, Picture shown below the merging Network

• The IP Traffic flows sending traffic from London Office to three destination North-wales Plant, Birmingham Plant and Oxford Office. We defined IP Traffic according to given table.
• A New Link DS_1 ( Black Line in Picture ) introduced which connects North-wales Plant to London Office via The New Manchester Office.
• We runs RIP as routing Protocol which gives us Following observations:

Utilization

From Graph it is clearly showing that utilisation is high for London office to Manchester office and Manchester Office to North Wales

Both are approximately 97 % utilisation which is overutilization and cause serious problems to the network.

For London to oxford office and Oxford to Birmingham Plant the utilisation is nearly 13% and 6% this is because of link using high data rate cable DS3 where we get the low utilisation and low data rate comparatively where we get lower data rate cable.

DS1 cable has data rate of 1.5Mbps which DS3 has 44.736 Mbps

With this Observation , we come to know that one possible solution is using EIGRP protocol , as EIGRP protocol solve the over utilisation problem from our network.

Lets see by running the EIGRP protocols and compare the result of it with RIP

The EIGRP protocol solves the Over utilization problem we have faced in RIP protocol and the resultant graph and comparison is showing this clearly with evenly distributed utilization over selected path by EIGRP.

CONCLUSIONS : It can be seen that EIGRP compared to RIP performs better in terms of network convergence activity and Routing protocol traffic. EIGRP has the characteristics of both distance vector and link state protocols, has improved network convergence, reduced routing protocol traffic, and less CPU and RAM utilization compared to RIP

References:

Performance Analysis of RIP, EIGRP, and OSPF using OPNET By Don Xu and Ljiljana Trajković

Dynamic Routing Protocol Implementation Decision between EIGRP, OSPF and RIP Based on Technical Background Using OPNET Modeller By Thornier, S.G.