How to implement bgp protocol in ns2
To implement the Border Gateway Protocol (BGP) using NS2 (Network Simulator 2) is more difficult than other routing protocols such as RIP since BGP protocol is an inter-domain routing protocol which deals with policies, path vector mechanisms, and the management of routing tables among the autonomous systems (AS). The simulation tool NS2 does not have native aid for BGP, so we executing it has includes either expanding the NS2’s capabilities over the C++ code or mimicking BGP-like performance using scripts.
Given below is a general procedure to executing BGP-like behaviour in NS2:
Step-by-Step Implementations:
- Set Up the NS2 Environment:
- Make sure that NS2 is installed on the system and that we are familiar including its simple functionality.
- Create the Network Topology:
- Define a topology that denotes several autonomous systems (AS). Every single AS will have its individual internal routers, and BGP is used to route among these ASes.
Example:
set ns [new Simulator]
set nf [open out.nam w]
$ns namtrace-all $nf
# Define nodes for different ASes
set AS1_R1 [$ns node]
set AS1_R2 [$ns node]
set AS2_R1 [$ns node]
set AS2_R2 [$ns node]
# Links within AS1
$ns duplex-link $AS1_R1 $AS1_R2 1Mb 10ms DropTail
# Links within AS2
$ns duplex-link $AS2_R1 $AS2_R2 1Mb 10ms DropTail
# BGP peering link between AS1 and AS2
$ns duplex-link $AS1_R2 $AS2_R1 512Kb 20ms DropTail
- Simulate BGP Behavior:
- Routing Information Exchange: To emulate the exchange of routing information among the ASes. In BGP, every AS advertises its individual network prefaces to its neighbours.
- Path Vector Mechanism: We execute a simple path vector mechanism in which every AS advertises the comprehensive path to an end network.
Example:
proc bgp_advertise {src dest} {
# Simulate advertisement of routes from src to dest
puts “BGP: Advertising routes from $src to $dest”
# Add route to routing table (simplified for simulation)
set path [list $src $dest]
return $path
}
proc bgp_update {src dest path} {
# Simulate a BGP update message
puts “BGP: Updating route from $src to $dest with path $path”
# Update routing table (simplified for simulation)
return $path
}
# Simulate BGP advertisements and updates
set path1 [bgp_advertise $AS1_R2 $AS2_R1]
set path2 [bgp_update $AS2_R1 $AS1_R2 $path1]
- Implement Policy-Based Routing:
- Policy Control: To execute the policies that control which routes are marketed or obtained. BGP permits the policies to be utilized based on prefix, path length, AS path, etc.
- Route Filtering: We execute the route filtering based on policies, mimicking decisions to accept or reject particular routes.
Example (Pseudocode):
proc bgp_policy {path} {
# Example policy: reject paths longer than 3 hops
if {[llength $path] > 3} {
puts “BGP: Rejecting path $path due to policy”
return 0
}
return 1
}
if {[bgp_policy $path2]} {
# Accept the route
puts “BGP: Route accepted: $path2”
} else {
# Reject the route
puts “BGP: Route rejected: $path2”
}
- Simulate Network Traffic:
- To emulate the traffic flows among the nodes in various ASes to monitor the influences of BGP routing.
- We can attach agents and describe traffic flows same to other NS2 simulations.
Example:
set udp0 [new Agent/UDP]
$ns attach-agent $AS1_R1 $udp0
set null0 [new Agent/Null]
$ns attach-agent $AS2_R2 $null0
$ns connect $udp0 $null0
set cbr [new Application/Traffic/CBR]
$cbr set packetSize_ 512
$cbr set rate_ 1Mb
$cbr attach-agent $udp0
$ns at 1.0 “$cbr start”
- Run the Simulation:
- To perform the simulation script and monitor the network behaviour over the trace files and NAM (Network Animator).
- Evaluate how the emulated BGP exchanges and policies influence the routing decisions in the network.
Example:
$ns at 20.0 “finish”
$ns run
- Analyse and Enhance:
- We can use the trace files to consider the routing paths selected then we can observe how BGP policies effect the traffic.
- To execute more advanced BGP characteristics such as Multi-Exit Discriminators (MED), AS Path Prepending, or BGP Confederations if required.
A stepwise method was executed for BGP protocol and it was implemented and analysed using the simulation tool ns2. We will be offered more details related this topic if needed.
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