Simon Knight

Network Simulator

Phase 61/67 (67%)

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Roadmap

Concept

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 Phase 61/67 (67%)
Language Rust
Started 2026

Roadmap

Why the Network Simulator?

Quick Start — Three-Router OSPF Example

Create 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

  - 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: eth2
        ip: 10.0.3.1/24

  - 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 the 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)

Discussion:

  1. Topology loaded — 3 routers, 2 hosts, 5 links
  2. OSPF converged — Routers exchanged LSAs, computed SPF
  3. Routes installed — FIBs populated with best paths
  4. Commands executed — show ip route, ping ran at scripted times
  5. Results output — ASCII tables showing routing tables and ping responses

Roadmap

Demo

netsim demo OSPF triangle: three routers form adjacencies, compute SPF, then a host pings across the network. ARP resolution, traceroute hop-by-hop path discovery, and convergence timing all visible.

Roadmap

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

# Network Simulator
netsim daemon start my-network topology.yaml

# Network Simulator
netsim daemon start my-network topology.yaml --tick-interval 50ms

The daemon runs continuously in the background, ticking the simulation at the specified interval. State files are stored in ~/.netsim/<name>/ — PID file, Unix domain socket for gRPC IPC, and structured log.

Execute One-Shot Commands

Run a single command against a device in a running daemon, get the result, and exit. Ideal for scripting and CI/CD:

# Network Simulator
$ netsim exec my-network r1 "show ip route"
Destination       Next Hop        Metric  Interface
10.0.1.0/24       —               0       eth2 (connected)
10.0.3.0/24       10.0.13.3       11      eth1 (OSPF)
10.0.12.0/24      —               0       eth0 (connected)
10.0.13.0/24      —               0       eth1 (connected)
10.0.23.0/24      10.0.12.2       20      eth0 (OSPF)

# Network Simulator
$ netsim exec my-network h1 "ping 10.0.3.10"
Ping 10.0.3.10: 5/5 packets received, 0% loss

# Network Simulator
$ netsim exec my-network r1 "show ip route --json"
[{"destination":"10.0.1.0/24","next_hop":"—","metric":0,"interface":"eth2","source":"connected"}, ...]

Attach an Interactive Console

netsim attach my-network r1

Opens a full interactive REPL session on the device. You’re effectively “logged in” to the simulated router with command history, tab completion, and abbreviated commands:

r1> sh ip ro
Destination       Next Hop        Metric  Interface
10.0.1.0/24       —               0       eth2 (connected)
10.0.12.0/24      —               0       eth0 (connected)
10.0.13.0/24      —               0       eth1 (connected)
10.0.3.0/24       10.0.13.3       11      eth1 (OSPF)
10.0.23.0/24      10.0.12.2       20      eth0 (OSPF)

r1> show interfaces
Interface  IP Address      MAC Address        Admin   Status
eth0       10.0.12.1/24    02:00:00:00:01:00  up      up
eth1       10.0.13.1/24    02:00:00:00:01:01  up      up
eth2       10.0.1.1/24     02:00:00:00:01:02  up      up

r1> show ospf neighbors
Neighbor ID     Interface  State   Priority  Dead Time
2.2.2.2         eth0       Full    1         38s
3.3.3.3         eth1       Full    1         36s

r1> show arp
IP Address      MAC Address        State     Age  Interface
10.0.12.2       02:00:00:00:02:00  Resolved  396  eth0
10.0.13.3       02:00:00:00:03:00  Resolved  396  eth1

Live interface management — shut down a link and watch the protocol reconverge in real time:

r1> interface shutdown eth0
Interface eth0 admin-down
[OSPF adjacency r1<->r2 torn down]

r1> sh ip ro
Destination       Next Hop        Metric  Interface
10.0.1.0/24       —               0       eth2 (connected)
10.0.13.0/24      —               0       eth1 (connected)
10.0.3.0/24       10.0.13.3       11      eth1 (OSPF)
10.0.23.0/24      10.0.13.3       21      eth1 (OSPF)
   ← traffic to r2 now routes via r3 (metric increased from 20 to 21)

r1> interface no shutdown eth0
Interface eth0 admin-up
[OSPF adjacency r1<->r2 re-establishing...]

r1> sh ip ro
   ← routes restored to original paths after reconvergence

JSON output on any show command for structured data:

r1> show ospf neighbors --json
[{"neighbor_id":"2.2.2.2","interface":"eth0","state":"Full","priority":1},
 {"neighbor_id":"3.3.3.3","interface":"eth1","state":"Full","priority":1}]

Console Features:

Roadmap

TUI Daemon Selector

Running netsim daemon with no subcommand launches an interactive TUI (built with ratatui) that lets you browse running daemons, select devices, and attach — all without memorizing names.

Level 1 — Daemon selector lists all running simulations:

┌─ Running Daemons ─────────────────────────────────────────┐
│                                                           │
│ > ospf-triangle  (PID 48291, 2h 15m)                     │
│     examples/ospf-triangle.yaml                           │
│                                                           │
│   sp-core         (PID 48305, 45m 12s)                    │
│     topologies/transitnet-sp-core.yaml                    │
│                                                           │
│   dc-fabric       (PID 49102, 3m 8s)                      │
│     topologies/spine-leaf-evpn.yaml                        │
│                                                           │
└───────────────────────────────────────────────────────────┘
 Up/Down: Navigate  Enter: Select  l: Logs  q: Quit

Press Enter to select a daemon, then Level 2 — Device selector shows all devices:

┌─ ospf-triangle: Devices ──────────────────────────────────┐
│                                                           │
│ > r1  (router)                                            │
│   r2  (router)                                            │
│   r3  (router)                                            │
│   h1  (host)                                              │
│   h3  (host)                                              │
│                                                           │
└───────────────────────────────────────────────────────────┘
 Up/Down: Navigate  Enter: Select  l: Logs  q: Back

Press Enter on a device to open an interactive console session. Press l at any point to open the log viewer showing real-time daemon events (protocol state changes, adjacency transitions, convergence events).

Roadmap

Daemon Management

# Network Simulator
$ netsim daemon list
NAME            PID    UPTIME   TOPOLOGY
ospf-triangle   48291  2h 15m   examples/ospf-triangle.yaml
sp-core         48305  45m 12s  topologies/transitnet-sp-core.yaml

# Network Simulator
$ netsim daemon status my-network
Daemon: my-network
PID: 48291
Uptime: 2h 15m 30s
Tick interval: 100ms
Topology: examples/ospf-triangle.yaml
Devices: r1 (router), r2 (router), r3 (router), h1 (host), h3 (host)

# Network Simulator
$ netsim daemon stop my-network

# Network Simulator
$ netsim daemon list --clean

Roadmap

CI/CD Integration Example

Start a daemon, run automated validation, collect results, tear down:

#!/bin/bash
# Network Simulator

# Network Simulator
netsim daemon start ci-test topology.yaml --tick-interval 10ms

# Network Simulator
sleep 2

# Network Simulator
ROUTES=$(netsim exec ci-test r1 "show ip route --json")
OSPF=$(netsim exec ci-test r1 "show ospf neighbors --json")
PING=$(netsim exec ci-test h1 "ping 10.0.3.10")

# Network Simulator
echo "$ROUTES" | jq -e '.[] | select(.destination == "10.0.3.0/24")' || exit 1
echo "$OSPF" | jq -e 'length == 2' || exit 1
echo "$PING" | grep -q "0% loss" || exit 1

# Network Simulator
netsim daemon stop ci-test

echo "All validations passed"

Failover Testing with Daemon Mode

Test link failure and reconvergence interactively:

# Network Simulator
$ netsim daemon start failover-test sp-core.yaml

# Network Simulator
$ netsim exec failover-test r1 "show ospf neighbors"
Neighbor ID     Interface  State   Priority  Dead Time
2.2.2.2         eth0       Full    1         38s
3.3.3.3         eth1       Full    1         36s

# Network Simulator
$ netsim exec failover-test r1 "interface shutdown eth0"
Interface eth0 admin-down

# Network Simulator
$ netsim exec failover-test r1 "show ip route"
10.0.23.0/24      10.0.13.3       21      eth1 (OSPF)

# Network Simulator
$ netsim exec failover-test r1 "interface no shutdown eth0"
$ sleep 1
$ netsim exec failover-test r1 "show ospf neighbors"
Neighbor ID     Interface  State   Priority  Dead Time
2.2.2.2         eth0       Full    1         38s      ← re-established
3.3.3.3         eth1       Full    1         36s

Why Use Daemon Mode?

Roadmap

Protocol Support

Layer 2

Protocol Status Notes
Ethernet ✓ MAC addressing, frame encapsulation
ARP ✓ Request/reply, cache management

Layer 3

Protocol Status Notes
IPv4 ✓ Forwarding, TTL decrement, fragmentation not supported
ICMP ✓ Echo (ping), Time Exceeded (traceroute), Destination Unreachable

Routing Protocols

Protocol Status Notes
Static ✓ Host default gateway
OSPF ✓ Point-to-point, Area 0, LSA Types 1 & 2, SPF via Dijkstra
IS-IS ✓ L1/L2 hierarchical routing, LSP flooding, SPF via Dijkstra
BGP ✓ iBGP/eBGP, communities, route reflectors, MP-BGP VPNv4

MPLS & Tunneling

Protocol Status Notes
MPLS ✓ Label imposition/swap/pop/pop-continue, LFIB, multi-label stacks
LDP ✓ Label distribution, targeted sessions
SR-MPLS ✓ Segment Routing with SRGB, Node-SIDs, SR-owned LFIB precedence
RSVP-TE ✓ Explicit-path tunnels, deterministic refresh, convergence gating
GRE ✓ Generic routing encapsulation, overlay tunnels
VRF ✓ Virtual routing and forwarding, L3VPN with RD/RT

Resilience & Telemetry

Protocol Status Notes
BFD ✓ Bidirectional forwarding detection, async mode
BMP ✓ RFC 7854 BGP Monitoring Protocol, post-decision export
PCAP ✓ Packet capture with MPLS-aware filtering, Wireshark compatible

Available Commands

All commands support prefix abbreviation (e.g., sh ip ro) and --json output for structured data.

Show Commands (Read-Only Introspection):

Command Purpose
show ip route [vrf <name>] Routing table (global or per-VRF)
show interfaces Interface status, IP, MAC, admin state
show arp ARP cache entries
show ospf neighbors OSPF adjacency state
show ospf database OSPF LSDB contents
show isis neighbors IS-IS adjacency state
show isis database IS-IS LSDB contents
show isis interfaces IS-IS interface status
show isis spf IS-IS SPF run information
show isis route IS-IS routing table
show bgp [summary] BGP Loc-RIB / neighbor overview
show bgp neighbors [<ip>] BGP neighbor details
show bgp vpn VPNv4 routes
show mpls [forwarding] MPLS FTN/LFIB tables
show mpls vpn-labels VPN label allocations
show ldp [bindings/neighbors] LDP session and label state
show bfd [sessions] BFD session status
show gre [tunnels] GRE tunnel status
show vrf [<name> [routes]] VRF list, details, or per-VRF routes
show sr Segment Routing state and SIDs
show rsvp [tunnels] RSVP-TE tunnel status
show traffic Traffic generator statistics

Data Plane Probes:

Command Purpose
ping <ip> [-c N] ICMP echo test
traceroute <ip> [-m TTL] Hop-by-hop path discovery
mpls ping <ip> [--vrf <name>] MPLS OAM echo test
mpls traceroute <ip> [--vrf <name>] MPLS OAM path discovery

Operational Configuration:

Command Purpose
route add <dest> via <nexthop> Add static route
interface shutdown <name> Admin-down interface (triggers protocol reconvergence)
interface no shutdown <name> Admin-up interface
mpls lfib add/del <label> ... Manipulate MPLS LFIB entries
mpls ftn add/del <prefix> ... Manipulate MPLS FTN entries
bgp vpn-originate <vrf> Trigger VPN route origination
gre tunnel set <iface> ... Configure GRE tunnel parameters

Roadmap

Example: IS-IS L1/L2 Hierarchy with Real Output

Service provider topology demonstrating IS-IS hierarchical routing:

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

Simulation Output:

$ 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

Roadmap

Use Cases

Roadmap

Milestones

v1.0 MVP (Shipped Jan 24, 2026) Tick-based simulation engine with deterministic execution.

v1.1 Scale & Features (Shipped Jan 31, 2026) Parallel execution, BGP, and traffic generation.

v1.2 Engine Hardening (Shipped Jan 31, 2026) Convergence detection and dynamic topology changes.

v1.3 Automation (Shipped Feb 1, 2026) Python bindings and REST API.

v1.4 Observability & Export (Shipped Feb 1, 2026) Packet capture and flow export.

v1.5 Protocol Foundation (Shipped Feb 5, 2026) Second IGP, sub-second failure detection, tunneling, and MPLS.

v1.6 L3VPN & Telemetry (Shipped Feb 11, 2026) VRF isolation, L3VPN services, RSVP-TE, and BGP monitoring.

v1.7 Segment Routing (Shipped Feb 14, 2026) SR-MPLS programming and traffic analysis.

v1.8 Data Center Fabric & EVPN (In Progress) EVPN control plane and VXLAN dataplane for data center fabrics.

Roadmap:

Tech Stack

Rust, Tokio for async execution, petgraph for topology representation, gRPC for daemon IPC, ratatui for TUI

Roadmap

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