Simon Knight

Network Simulator

52 (in progress) — daemon-mode-interactive-console

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The Insight

Developing agentic AI systems and network automation tools requires rapid iteration. Spinning up containers for every test cycle takes minutes; simulation takes seconds. This simulator enables fast prototyping of network automation agents, DevOps pipelines, and AI-driven network operations — validate configurations and agent logic in simulation before committing to heavyweight container deployments.

Quick Facts

   
Status 52 (in progress) — daemon-mode-interactive-console
Language Rust
Started 2026

What This Is

A Rust-based network simulator that models packet-level behavior for routing protocols. It provides a middle ground between pure algorithmic analysis (like C-BGP) and full emulation (like Containerlab) — larger scale and smaller footprint than emulation, higher fidelity than algorithmic simulation.

Key Features

Daemon Mode — Real-Time Network Interaction

Run simulations as background daemons and interact with them in real-time — like docker exec for network simulations.

Starting a Daemon

# Start a simulation as a background daemon
netsim daemon start my-network topology.yaml

# With custom tick rate (default: 100ms)
netsim daemon start my-network topology.yaml --tick-interval 50ms

The daemon runs continuously in the background, ticking the simulation at the specified interval.

Execute One-Shot Commands

# Run a single command on a device
netsim exec my-network r1 "show ip route"
netsim exec my-network h1 "ping 10.0.3.10"
netsim exec my-network r2 "show ospf neighbors"

Attach an Interactive Console

# Attach to a device for an interactive session
netsim attach my-network r1

Once attached, you get an interactive REPL with command history:

r1> show ip route
Destination       Next Hop        Metric  Interface
10.0.1.0/24       —               0       eth2 (connected)
10.0.12.0/24      —               0       eth0 (connected)
...

r1> show interfaces
Interface  IP Address      MAC Address        Status
eth0       10.0.12.1/24    02:00:00:00:01:00  up
eth1       10.0.13.1/24    02:00:00:00:01:01  up
...

r1> ping 10.0.3.10
Ping 10.0.3.10: 5/5 packets received, 0% loss
...

r1> exit

Type help in the console for available commands, or exit to detach.

Daemon Management

# Check daemon status
netsim daemon status my-network

# Stop a daemon
netsim daemon stop my-network

Why Use Daemon Mode?

Available Commands in Daemon Mode

All commands from netsim run work in daemon mode via exec or attach:

Detailed Protocol Support

Layer 2: Data Link

Layer 3: Network

OSPF (RFC 2328 - OSPFv2):

IS-IS (ISO 10589):

BGP (RFC 4271 - BGP-4):

MPLS - Planned:

Example 1: OSPF Triangle Topology

Simple three-router topology to verify basic OSPF functionality.

Input topology (ospf-triangle.yaml):

name: ospf-triangle
description: Three OSPF routers in a triangle with hosts

devices:
  - name: r1
    type: router
    router_id: 1.1.1.1
    interfaces:
      - name: eth0
        ip: 10.0.12.1/24
        ospf: { area: 0, cost: 10 }
      - name: eth1
        ip: 10.0.13.1/24
        ospf: { area: 0, cost: 10 }
      - name: eth2
        ip: 10.0.1.1/24
        ospf: { area: 0, cost: 1 }

  - name: r2
    type: router
    router_id: 2.2.2.2
    interfaces:
      - name: eth0
        ip: 10.0.12.2/24
        ospf: { area: 0, cost: 10 }
      - name: eth1
        ip: 10.0.23.2/24
        ospf: { area: 0, cost: 10 }

  - name: r3
    type: router
    router_id: 3.3.3.3
    interfaces:
      - name: eth0
        ip: 10.0.13.3/24
        ospf: { area: 0, cost: 10 }
      - name: eth1
        ip: 10.0.23.3/24
        ospf: { area: 0, cost: 10 }

  - name: h1
    type: host
    interfaces:
      - name: eth0
        ip: 10.0.1.10/24
        gateway: 10.0.1.1

  - name: h3
    type: host
    interfaces:
      - name: eth0
        ip: 10.0.3.10/24
        gateway: 10.0.3.1

links:
  - endpoints: [r1:eth0, r2:eth0]
  - endpoints: [r1:eth1, r3:eth0]
  - endpoints: [r2:eth1, r3:eth1]
  - endpoints: [r1:eth2, h1:eth0]
  - endpoints: [r3:eth2, h3:eth0]

script:
  - at: converged
    device: r1
    command: show ip route
  - at: converged + 100
    device: h1
    command: ping 10.0.3.10

Run simulation:

$ netsim run ospf-triangle.yaml

[t=0ms] Network initialized: 5 devices, 5 links
[t=0ms] OSPF: r1, r2, r3 sending Hello on all interfaces
[t=10ms] OSPF: Neighbors established (r1<->r2, r1<->r3, r2<->r3)
[t=15ms] OSPF: LSA flooding in progress
[t=20ms] OSPF: SPF calculation complete on all routers
[t=20ms] Network converged

[t=20ms] r1> show ip route
10.0.1.0/24   directly connected (eth2)
10.0.3.0/24   via 10.0.13.3 [OSPF/110] metric=11
10.0.12.0/24  directly connected (eth0)
10.0.13.0/24  directly connected (eth1)
10.0.23.0/24  via 10.0.12.2 [OSPF/110] metric=20

[t=120ms] h1> ping 10.0.3.10
PING 10.0.3.10: 64 bytes from 10.0.3.10: icmp_seq=1 ttl=62 time=2.1ms
Round-trip path: h1 -> r1 -> r3 -> h3 -> r3 -> r1 -> h1

Simulation complete: 120ms simulated, 0.034s real time (3529x speedup)

Example 2: IS-IS Level 1/Level 2 Hierarchy

Service provider topology demonstrating IS-IS hierarchical routing with L1 and L2 areas.

Input topology (isis-hierarchy.yaml):

name: isis-hierarchy
description: IS-IS L1/L2 hierarchy with inter-area routing

devices:
  - name: r1
    type: router
    isis:
      net: "49.0001.0000.0000.0001.00"
      level: l1
    interfaces:
      - name: eth0
        ip: 10.1.0.1/24
        isis: { metric: 10 }
      - name: lo
        ip: 192.0.2.1/32
        isis: {}

  - name: r2
    type: router
    isis:
      net: "49.0001.0000.0000.0002.00"
      level: l1l2  # Area border router
    interfaces:
      - name: eth0
        ip: 10.1.0.2/24
        isis: { metric: 10 }
      - name: eth1
        ip: 10.0.0.2/24
        isis: { metric: 10 }
      - name: lo
        ip: 192.0.2.2/32
        isis: {}

  - name: r3
    type: router
    isis:
      net: "49.0002.0000.0000.0003.00"
      level: l2
    interfaces:
      - name: eth0
        ip: 10.0.0.3/24
        isis: { metric: 10 }
      - name: lo
        ip: 192.0.2.3/32
        isis: {}

links:
  - endpoints: [r1:eth0, r2:eth0]
  - endpoints: [r2:eth1, r3:eth0]

script:
  - at: converged
    device: r2
    command: show isis neighbors
  - at: converged
    device: r2
    command: show isis database
  - at: converged
    device: r1
    command: show ip route

Run simulation:

$ netsim run isis-hierarchy.yaml

[t=0ms] Network initialized: 3 devices, 2 links
[t=0ms] IS-IS: r1, r2, r3 sending IIH (IS-IS Hello)
[t=3ms] IS-IS: Adjacencies forming
[t=5ms] IS-IS: r1<->r2 L1 adjacency Up
[t=5ms] IS-IS: r2<->r3 L2 adjacency Up
[t=8ms] IS-IS: LSP flooding in progress
[t=12ms] IS-IS: SPF calculation complete (L1 and L2)
[t=12ms] Network converged

[t=12ms] r2> show isis neighbors
System ID       Interface  State  Level  Holdtime
0000.0000.0001  eth0       Up     L1     24s
0000.0000.0003  eth1       Up     L2     24s

[t=12ms] r2> show isis database
IS-IS Level-1 Link State Database:
LSPID                 LSP Seq Num  Checksum  Lifetime  Attributes
0000.0000.0001.00-00  0x00000003   0x4a2e    864       L1
0000.0000.0002.00-00  0x00000003   0x5c1a    864       L1L2

IS-IS Level-2 Link State Database:
LSPID                 LSP Seq Num  Checksum  Lifetime  Attributes
0000.0000.0002.00-00  0x00000003   0x7f3c    864       L1L2
0000.0000.0003.00-00  0x00000003   0x9a2b    864       L2

[t=12ms] r1> show ip route
Codes: C - connected, i L1 - IS-IS level-1, i L2 - IS-IS level-2

C    10.1.0.0/24 is directly connected, eth0
C    192.0.2.1/32 is directly connected, lo
i L1 192.0.2.2/32 [115/10] via 10.1.0.2, eth0
i L2 192.0.2.3/32 [115/20] via 10.1.0.2, eth0
     (route leaked from L2 to L1 by ABR r2)

Simulation complete: 15ms simulated, 0.008s real time
IS-IS events: 18 hellos, 4 LSPs, 2 SPF runs

Example 3: Protocol State Inspection (OSPF)

Detailed protocol state inspection with full routing tables and OSPF database dumps.

[t=45ms] core-1> show ip route
Codes: C - connected, O - OSPF, IA - OSPF inter-area
       * - candidate default

Gateway of last resort is not set

C    10.0.0.0/30 is directly connected, eth0
C    10.0.0.4/30 is directly connected, eth1
C    10.0.0.8/30 is directly connected, eth2
C    10.0.100.1/32 is directly connected, lo0
O    10.0.100.2/32 [110/10] via 10.0.0.2, eth0, 00:00:25
O    10.0.100.3/32 [110/10] via 10.0.0.6, eth1, 00:00:25
O    10.0.100.4/32 [110/10] via 10.0.0.10, eth2, 00:00:25
O    10.5.1.0/24 [110/20] via 10.0.0.2, eth0, 00:00:23
O    10.5.2.0/24 [110/20] via 10.0.0.6, eth1, 00:00:23
O    10.5.12.0/24 [110/20] via 10.0.0.2, eth0, 00:00:23
                  [110/20] via 10.0.0.6, eth1, 00:00:23
O IA 10.10.1.0/24 [110/25] via 10.0.0.10, eth2, 00:00:20
O IA 10.10.2.0/24 [110/25] via 10.0.0.10, eth2, 00:00:20

[t=45ms] core-1> show ip ospf database

       OSPF Router with ID (10.0.100.1) (Process ID 1)

                Router Link States (Area 0.0.0.0)

Link ID         ADV Router      Age  Seq#       Checksum
10.0.100.1      10.0.100.1      25   0x80000003 0x6d2a
10.0.100.2      10.0.100.2      23   0x80000003 0x7f1c
10.0.100.3      10.0.100.3      24   0x80000003 0x8b0e
10.0.100.4      10.0.100.4      22   0x80000004 0x9700

                Net Link States (Area 0.0.0.0)

Link ID         ADV Router      Age  Seq#       Checksum
10.0.0.1        10.0.100.1      25   0x80000001 0x4a12
10.0.0.5        10.0.100.1      25   0x80000001 0x5b23
10.5.12.2       10.0.100.2      23   0x80000002 0x7c45

                Summary Net Link States (Area 0.0.0.0)

Link ID         ADV Router      Age  Seq#       Checksum
10.10.1.0       10.0.100.4      20   0x80000001 0xa1f3
10.10.2.0       10.0.100.4      20   0x80000001 0xb2e4

[t=45ms] core-1> show ip ospf database router 10.0.100.1

       OSPF Router with ID (10.0.100.1) (Process ID 1)

                Router Link States (Area 0.0.0.0)

  LS age: 25
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 10.0.100.1
  Advertising Router: 10.0.100.1
  LS Seq Number: 0x80000003
  Checksum: 0x6d2a
  Length: 60
  Number of Links: 3

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 10.0.0.1
     (Link Data) Router Interface address: 10.0.0.1
      Number of TOS metrics: 0
       TOS 0 Metrics: 10

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 10.0.0.5
     (Link Data) Router Interface address: 10.0.0.5
      Number of TOS metrics: 0
       TOS 0 Metrics: 10

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 10.0.0.9
     (Link Data) Router Interface address: 10.0.0.9
      Number of TOS metrics: 0
       TOS 0 Metrics: 10

[t=45ms] core-1> show ip protocols
Routing Protocol is "ospf 1"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Router ID 10.0.100.1
  Number of areas in this router is 1. 1 normal 0 stub 0 nssa
  Maximum path: 4
  Routing for Networks:
    10.0.0.0 0.0.0.3 area 0.0.0.0
    10.0.0.4 0.0.0.3 area 0.0.0.0
    10.0.0.8 0.0.0.3 area 0.0.0.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    10.0.100.2      110           00:00:25
    10.0.100.3      110           00:00:24
    10.0.100.4      110           00:00:22
  Distance: (default is 110)

[t=45ms] core-1> show ip ospf interface eth0
eth0 is up, line protocol is up
  Internet Address 10.0.0.1/30, Area 0.0.0.0
  Process ID 1, Router ID 10.0.100.1, Network Type BROADCAST, Cost: 10
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 10.0.100.1, Interface Address 10.0.0.1
  Backup Designated router (ID) 10.0.100.2, Interface Address 10.0.0.2
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    Hello due in 00:00:07
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 10.0.100.2 (Backup Designated Router)
  Suppress hello for 0 neighbor(s)

Example 4: BGP Multi-AS Route Propagation

eBGP peering across three autonomous systems with route propagation and path attribute handling.

Input topology (bgp-multi-as.yaml):

name: bgp-multi-as
description: BGP propagation across multiple ASes with communities

devices:
  - name: r1
    type: router
    router_id: 1.1.1.1
    interfaces:
      - name: lo0
        ip: 1.1.1.1/32
      - name: eth0
        ip: 10.0.12.1/24
    bgp:
      as: 65001
      networks: ["10.1.0.0/24"]
      neighbors:
        - ip: 10.0.12.2
          remote_as: 65002
          send_community: true

  - name: r2
    type: router
    router_id: 2.2.2.2
    interfaces:
      - name: lo0
        ip: 2.2.2.2/32
      - name: eth0
        ip: 10.0.12.2/24
      - name: eth1
        ip: 10.0.23.2/24
    bgp:
      as: 65002
      neighbors:
        - ip: 10.0.12.1
          remote_as: 65001
        - ip: 10.0.23.3
          remote_as: 65003

  - name: r3
    type: router
    router_id: 3.3.3.3
    interfaces:
      - name: lo0
        ip: 3.3.3.3/32
      - name: eth0
        ip: 10.0.23.3/24
    bgp:
      as: 65003
      neighbors:
        - ip: 10.0.23.2
          remote_as: 65002

links:
  - endpoints: [r1:eth0, r2:eth0]
  - endpoints: [r2:eth1, r3:eth0]

script:
  - at: converged
    device: r2
    command: show bgp summary
  - at: converged
    device: r3
    command: show bgp

Run simulation:

$ netsim run bgp-multi-as.yaml

[t=0ms] Network initialized: 3 devices, 2 links
[t=0ms] BGP: r1, r2, r3 establishing sessions
[t=5ms] BGP: r1<->r2 session established (eBGP AS65001-AS65002)
[t=5ms] BGP: r2<->r3 session established (eBGP AS65002-AS65003)
[t=10ms] BGP: r1 advertising 10.1.0.0/24
[t=12ms] BGP: Route propagation in progress
[t=15ms] Network converged

[t=15ms] r2> show bgp summary
BGP router identifier 2.2.2.2, local AS number 65002

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
10.0.12.1       4 65001       3       3        1    0    0 00:00:15        1
10.0.23.3       4 65003       3       3        1    0    0 00:00:15        0

Total number of neighbors 2

[t=15ms] r3> show bgp
BGP table version is 1, local router ID is 3.3.3.3
Status codes: s suppressed, d damped, h history, * valid, > best, i internal
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 10.1.0.0/24      10.0.23.2                0             0 65002 65001 i

Total number of prefixes 1

Path details:
  10.1.0.0/24:
    AS_PATH: 65002 65001
    NEXT_HOP: 10.0.23.2
    ORIGIN: IGP
    MED: not set
    LOCAL_PREF: not set (eBGP)
    Communities: (none)

Simulation complete: 18ms simulated, 0.009s real time
BGP events: 6 sessions established, 1 route originated, 2 UPDATEs sent

Limitations

Use Cases

Roadmap

Current Status

v1.6 shipped with OSPF support. 126,000 lines of Rust, 122 requirements met (35 MVP + 87 advanced).

Tech Stack

Rust, Tokio for async execution, petgraph for topology representation

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