To simulate Interior Gateway Protocols (IGPs) in NS2 has needs to setup the routing protocols that perform in an autonomous system (AS). The frequent IGPs that contain routing information protocol (RIP) and Open Shortest Path First (OSPF). NS2 supports RIP out of the box using the Distance Vector (DV) method, however for more advanced simulations such as OSPF, we required expand the NS2 or utilize external libraries.
In the below, we deliver the step-by-step procedures to achieve this approach in ns2.
Steps to Simulate Interior Protocol Projects in NS2
- Install NS2
Make sure that NS2 is installed on the system. We can install it on Linux-based systems using the following command:
sudo apt-get install ns2
For Windows, we need to utilize Cygwin or download a precompiled version of NS2.
- Simulating RIP (Routing Information Protocol)
Step-by-Step RIP Simulation
RIP is a simple Interior Gateway Protocol (IGP) that utilize distance vector routing to control the optimal path according to hop count. Here’s a basic TCL script to simulate RIP in NS2.
Example TCL Script for RIP Simulation
# Define simulator object
set ns [new Simulator]
# Open trace file to log simulation results
set tracefile [open rip_igp.tr w]
$ns trace-all $tracefile
# Open NAM file to visualize simulation
set namfile [open rip_igp.nam w]
$ns namtrace-all $namfile
# Define the number of nodes and simulation time
set val(nn) 4 ;# Number of nodes (routers)
set val(stop) 20.0 ;# Simulation stop time
set val(routing) DV ;# Use Distance Vector (RIP-like protocol)
# Create the nodes (representing routers)
for {set i 0} {$i < $val(nn)} {incr i} {
set node_($i) [$ns node]
}
# Create duplex links between the nodes (wired network)
$ns duplex-link $node_(0) $node_(1) 10Mb 10ms DropTail
$ns duplex-link $node_(1) $node_(2) 10Mb 10ms DropTail
$ns duplex-link $node_(2) $node_(3) 10Mb 10ms DropTail
$ns duplex-link $node_(3) $node_(0) 10Mb 10ms DropTail
# Enable RIP protocol (Distance Vector)
$ns rtproto $val(routing)
# Setup traffic between nodes using UDP
set udp0 [new Agent/UDP]
$ns attach-agent $node_(0) $udp0
set null0 [new Agent/Null]
$ns attach-agent $node_(2) $null0
$ns connect $udp0 $null0
# Create a CBR (Constant Bit Rate) traffic source over UDP
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 512
$cbr0 set interval_ 0.01
$cbr0 attach-agent $udp0
# Start traffic at time 1.0 second
$ns at 1.0 “$cbr0 start”
$ns at 19.0 “$cbr0 stop”
# End the simulation after 20 seconds
$ns at $val(stop) “finish”
# Procedure to end the simulation
proc finish {} {
global ns tracefile namfile
$ns flush-trace
close $tracefile
close $namfile
exec nam rip_igp.nam &
exit 0
}
# Run the simulation
$ns run
Explanation of the Script
- Nodes: Four nodes (representing routers) are generated and interrelated with duplex links.
- RIP Protocol: The routing protocol is set to Distance Vector (DV), that replicate RIP-like behaviour.
- Traffic: UDP traffic is generated among two routers, and the traffic pattern is defined using CBR (Constant Bit Rate).
- Simulation End: The simulation executes for 20 seconds, after which it terminate.
- Running the Simulation
To execute the simulation, save the script as rip_igp.tcl, and then run it with NS2:
ns rip_igp.tcl
- Visualizing the Simulation
Once the simulation is done, we can envision the network traffic and topology using the NAM (Network Animator):
nam rip_igp.nam
This will open the NAM visualization tool, in which we can track the network behaviour, packet flow, and routing updates.
- Analysing the Trace File
The trace file (rip_igp.tr) encompasses detailed logs of packet transmissions, routing updates, and drops. We need to evaluate it using AWK, Python, or other tools to estimate parameters such as:
- Packet Delivery Ratio
- End-to-End Delay
- Routing Overhead
- Simulating OSPF-Like Behavior in NS2
NS2 does not natively support OSPF (Open Shortest Path First) directly, however we can replicate OSPF-like behaviour by set up link-state routing protocols or by using custom extensions. OSPF is a more complex protocol related to RIP, as it utilizes Link State Routing (LSR) and needs topology information to be shared via all routers.
If we need to replicate OSPF, here are two options:
Option 1: Customizing Link-State Routing in NS2
NS2 supports Link-State Routing via extensions or by replicates the features using a custom protocol. To replicate OSPF-like behaviour, we will required to configured link-state routing in which each node distributes its entire link-state database with neighbouring nodes.
Here’s how we can describe Link-State Routing:
# Enable Link-State routing protocol (Custom implementation)
$ns rtproto LS
This permits Link State (LS) routing in NS2. We would require customizing the way packets are transmitted and execute OSPF’s certain characteristics like:
- Area-based routing
- Designated Routers (DR) and Backup DR
- Flooding of link-state advertisements (LSAs)
Option 2: External Extensions or Libraries
Some external NS2 extensions and libraries deliver an OSPF support. We can download and install these extensions to replicate an OSPF more precisely. These cannot be officially maintained, however they can be helpful for OSPF-based projects.
- Simulating OSPF-like Network with Link State
Here is a basic instance which replicates a Link State routing mechanism that implements OSPF’s approach:
# Define the simulator object
set ns [new Simulator]
# Open trace file and NAM file
set tracefile [open ospf_linkstate.tr w]
$ns trace-all $tracefile
set namfile [open ospf_linkstate.nam w]
$ns namtrace-all $namfile
# Create nodes for routers
for {set i 0} {$i < 4} {incr i} {
set node_($i) [$ns node]
}
# Create duplex links
$ns duplex-link $node_(0) $node_(1) 10Mb 10ms DropTail
$ns duplex-link $node_(1) $node_(2) 10Mb 10ms DropTail
$ns duplex-link $node_(2) $node_(3) 10Mb 10ms DropTail
$ns duplex-link $node_(3) $node_(0) 10Mb 10ms DropTail
# Enable Link State Routing protocol
$ns rtproto LS
# Create UDP traffic
set udp0 [new Agent/UDP]
$ns attach-agent $node_(0) $udp0
set null0 [new Agent/Null]
$ns attach-agent $node_(2) $null0
$ns connect $udp0 $null0
# Configure CBR traffic
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 512
$cbr0 set interval_ 0.01
$cbr0 attach-agent $udp0
# Start traffic at 1 second
$ns at 1.0 “$cbr0 start”
$ns at 19.0 “$cbr0 stop”
# End simulation
$ns at 20.0 “finish”
proc finish {} {
global ns tracefile namfile
$ns flush-trace
close $tracefile
close $namfile
exec nam ospf_linkstate.nam &
exit 0
}
# Run simulation
$ns run
- Modifying and Extending the Simulation
We can expand the simple simulation by:
- Adding more nodes: mimic larger networks.
- Changing traffic patterns: Utilize TCP or replicate real-world application protocols such as FTP or HTTP.
- Comparing performance: Assess the parameters such as throughput, delay in diverse routing configurations (RIP vs. OSPF).
The given above simulation process was successfully and effectively simulated by using ns2 tool for Interior Gateway Protocols and also we provide the sample snippets for OSPF and LSR, detailed explanation scrip and the extension of simulation scenarios. Additional details will be updated later.
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