To simulate the Border Gateway Protocol (BGP) in NS2 has includes to design an inter-domain routing, in which the routers interchange routing information among different autonomous systems (ASes). Since NS2 doesn’t directly support BGP, we can replicate its characteristics by generating custom scripts that implement BGP functionality, like path vector routing, routing advertisements, and route selection policies.
You can consistently depend on us for optimal simulation guidance, as we provide customized support to meet your specific needs.
This manual outlines the steps to simulate BGP-like behaviour in NS2.
Steps to Simulate BGP Protocol in NS2
- Install NS2:
- Make sure NS2 is installed and configured properly. We can install it on a Linux system or utilize Cygwin if you’re on Windows.
- Define Network Topology:
- In BGP simulations, we usually have multiple autonomous systems (ASes), each with its own router. We will need to describe these ASes and the links among their routers.
Example Topology with Multiple Autonomous Systems:
set ns [new Simulator]
# AS1 routers
set as1_router1 [$ns node]
set as1_router2 [$ns node]
# AS2 routers
set as2_router1 [$ns node]
set as2_router2 [$ns node]
# AS3 router
set as3_router [$ns node]
# Create links between routers in the same AS
$ns duplex-link $as1_router1 $as1_router2 10Mb 10ms DropTail
$ns duplex-link $as2_router1 $as2_router2 10Mb 10ms DropTail
# Create inter-AS links
$ns duplex-link $as1_router2 $as2_router1 10Mb 20ms DropTail
$ns duplex-link $as2_router2 $as3_router 10Mb 30ms DropTail
- Simulate Path Vector Routing (BGP Behavior):
- BGP utilizes path vector routing, in which each router advertises the complete path to a destination to its neighbours. We can replicate this by generating routing table updates that propagate via the ASes.
Example: Path Vector Routing Simulation
proc bgp_advertise {src dst path} {
puts “BGP Update: $src is advertising path $path to $dst”
# Simulate routing table update at the destination
bgp_update $dst $path
}
proc bgp_update {router path} {
puts “Router $router has updated its routing table with path $path”
}
- Implement BGP Route Selection Policies:
- BGP routers choose the best path according to numerous factors, that contain the length of the AS path and local policies. We can replicate this by having each router to measure multiple paths and select the best one.
Example: BGP Route Selection
proc bgp_route_selection {router paths} {
set best_path “”
set min_length 99999
# Find the shortest AS path
foreach path $paths {
set length [llength $path]
if {$length < $min_length} {
set min_length $length
set best_path $path
}
}
puts “Router $router has selected path $best_path”
}
We can adapt this to contain other factors, like local preferences or next-hop reachability.
- Simulate Traffic Flow:
- Once the routes are introduced, mimic the traffic among routers in different ASes using agents and applications.
Example: Simulating Traffic Between ASes
set tcp [new Agent/TCP]
set sink [new Agent/TCPSink]
# Attach TCP agent to routers
$ns attach-agent $as1_router1 $tcp
$ns attach-agent $as3_router $sink
# Connect agents to simulate traffic
$ns connect $tcp $sink
# Set up a traffic generator (FTP over TCP)
set ftp [new Application/FTP]
$ftp attach-agent $tcp
$ns at 1.0 “$ftp start”
- Simulate BGP Session Establishment:
- Replicate the establishment of BGP sessions among the routers in different ASes by designing the TCP connections BGP utilizes to interchange routing information.
Example: Establishing BGP Sessions
proc bgp_session_establish {router1 router2} {
puts “Establishing BGP session between $router1 and $router2”
# Simulate TCP connection establishment
set tcp_session [new Agent/TCP]
$ns attach-agent $router1 $tcp_session
$ns attach-agent $router2 $tcp_session
puts “BGP session established between $router1 and $router2”
}
# Establish session between AS1 and AS2 routers
$ns at 0.5 “bgp_session_establish as1_router2 as2_router1”
- Simulate BGP Route Propagation and Convergence:
- Replicate the propagation of BGP routing updates via the network and how routers converge on stable routes after a period of time.
Example: Simulating Route Propagation
# Propagate BGP route updates at time intervals
$ns at 1.0 “bgp_advertise as1_router1 as1_router2 {AS1}”
$ns at 1.5 “bgp_advertise as1_router2 as2_router1 {AS1 AS2}”
$ns at 2.0 “bgp_advertise as2_router2 as3_router {AS1 AS2 AS3}”
- Simulate BGP Failures:
- Replicate link or node failures to track on how BGP manage routing changes and how the routers converge on new paths.
Example: Simulating Link Failure
# Simulate a failure in the link between AS1 and AS2 routers
$ns at 3.0 “$ns rtmodel-at 3.0 down $as1_router2 $as2_router1”
# Simulate the router finding an alternative path or updating routes
$ns at 3.5 “bgp_route_selection as1_router2 {AS1 AS3}”
- Use Trace Files to Log Events:
- Utilize NS2’s tracing functionality to log routing updates, path selections, and traffic flow. This can be utilized to measure BGP’s behaviour and the convergence time.
Example: Enable Tracing
set tracefile [open bgp_simulation.tr w]
$ns trace-all $tracefile
We need to evaluate these trace files to track the interchange of routing information and monitor on how BGP converges.
- Run the Simulation:
- After configuring the topology, traffic, and BGP behavior, executes the NS2 simulation.
$ns run
- Analyze Results:
- Evaluate the trace files to assess key performance indicators of the BGP protocol, like convergence time, routing stability, and route selection policies.
Example: Measuring Routing Updates in Trace Files
awk ‘/BGP Update/ {print $0}’ bgp_simulation.tr
Advanced Features for BGP Simulation
- AS Path Preferences:
- Replicate AS path preferences by having each AS prefer specific paths according to local policies such as shortest path or avoiding specific ASes.
Example: Setting AS Path Preferences
proc set_path_preference {router path} {
if {[lindex $path 0] == “AS2”} {
puts “Router $router prefers path $path”
}
}
- Route Filtering:
- Apply route filtering, in which an AS decides not to accept or advertise certain routes, replicating real-world BGP policies.
Example: Filtering Routes
proc filter_routes {src dst path} {
if {[lsearch $path “AS3”] >= 0} {
puts “Router $src filtering out path $path”
return
}
puts “Router $src advertising path $path to $dst”
}
- BGP Route Flapping:
- Replicate route flapping, in which routes become unstable and frequently change because of network challenges, and implement mechanisms such as route dampening to prevent this.
Example: Route Flapping Simulation
$ns at 5.0 “bgp_advertise as1_router1 as2_router1 {AS1}”
$ns at 6.0 “$ns rtmodel-at 6.0 down $as1_router2 $as2_router1”
$ns at 7.0 “$ns rtmodel-at 7.0 up $as1_router2 $as2_router1”
Metrics for BGP Simulation Analysis
- Convergence Time: Time taken for all BGP routers to agree on the best routes after a alters in the network.
- Path Diversity: Number of available paths to reach a destination.
- Routing Table Size: Amount of routes stored in each router’s routing table.
- Traffic Flow: The key metrics like throughput, packet loss, and latency via the ASes.
- Routing Stability: Frequency of route changes and the effects of route flapping.
With the help of this procedure you can obtain the knowledge and can be able to simulate the Border Gateway Protocol projects in ns2 tool. Additional specific details regarding the Border Gateway Protocol projects also provided.
