splithorizon · SONiC on GNS3
splithorizon FIELD NOTES · DISAGGREGATED NETWORKING Getting started with SONiC on GNS3 SONiC 202311 · GNS3 2.2.x Paul Carvill · CCIE #16661 Emeritus splithorizon.cloud Open-source NOS simulation — full containerised daemon stack, no hardware required WHAT IS SONIC SONiC (Software for Open Networking in the Cloud) is Microsoft's open-source NOS, born from the Azure merchant-silicon fleet. It runs on any ASIC with a SAI driver — Broadcom, NVIDIA/Mellanox, Intel/Barefoot. The architecture separates the control plane into containerised daemons (bgpd, lldpd, snmpd, syncd) communicating over a central Redis database. The VS image swaps the ASIC for a software dataplane — every daemon, CLI command, and config workflow is authentic. What you test here runs on real iron. PREREQUISITES SOFTWARE GNS3 2.2.x Server + GUI. GNS3 VM recommended for stable QEMU on any host OS. SONiC VS image Download sonic-vs.img.gz from sonic.software Image format conversion Convert .img.gz → .qcow2 before importing to GNS3 QEMU template. QEMU/KVM GNS3 VM 202311 stable HARDWARE & HOST RAM — ~2 GB per SONiC node Plan your topology before adding devices. A 3-node spine-leaf needs ~6 GB available. Virtualisation KVM/QEMU on Linux preferred. GNS3 VM on ESXi is ideal for nested virt. Adapter type — virtio only Must set virtio in QEMU template. e1000 causes interface mapping failures. Linux KVM ESXi + VM IMAGE PREPARATION bash · GNS3 VM # step 1 — decompress gunzip sonic-vs.img.gz # step 2 — convert to qcow2 qemu-img convert \ -f raw -O qcow2 \ sonic-vs.img \ sonic-vs.qcow2 # step 3 — verify (expect ~4–5 GB qcow2) qemu-img info sonic-vs.qcow2 # format: qcow2 virtual size: ~4.5G # Then: GNS3 → Preferences → QEMU VMs → New → upload GNS3 QEMU TEMPLATE 1 Preferences → QEMU VMs → New Upload the qcow2 to GNS3 server images folder 2 RAM 2048 MB · vCPUs 2 · Adapter: virtio Never use e1000 — interface mapping will break 3 Console type = telnet · boot headless Default creds: admin / YourPaSsWoRd (202311+) 4 Wait for docker ps — all containers Up Takes 60–90 s after boot. Don't configure before this. 5 Configure interfaces · save config sudo config save -y → persists to config_db.json ARCHITECTURE OVERVIEW GNS3 · QEMU · virtio interfaces bgpd FRRouting container lldpd discovery container snmpd monitoring container syncd SAI proxy container teamd / natd LAG / NAT containers Redis · CONFIG_DB · APP_DB · STATE_DB · ASIC_DB · COUNTER_DB SAI interface · VS software switch Linux kernel dataplane · vs datapath syncd translates ASIC_DB writes to SAI calls — in VS mode this targets the kernel software switch, not real silicon. ESSENTIAL CLI interface config # bring up interface sudo config interface startup Ethernet0 # assign IP address sudo config interface ip add Ethernet0 10.0.0.0/31 sudo config save -y vtysh — FRRouting BGP config sudo vtysh router bgp 65001 bgp router-id 10.0.0.1 neighbor 10.0.0.0 remote-as 65000 address-family ipv4 unicast network 192.168.1.0/24 exit-address-family VERIFICATION show interfaces status Port state, speed, MTU show ip bgp summary BGP peer state + prefix count show ip route FIB — kernel + BGP routes show arp ARP table — confirm L2 reachability docker ps All containers should show Up debugging # watch BGP convergence watch -n1 "show ip bgp sum" # tail syncd logs docker logs -f syncd # inspect ASIC_DB routes redis-cli -n 1 KEYS "ROUTE_ENTRY*" # reload without reboot sudo config reload -y COMMON PITFALLS Interface naming GNS3 adapters map to Ethernet0, Ethernet4… in steps of 4. Sequential numbering doesn't exist. e0→Ethernet0 e1→Ethernet4 e2→Ethernet8 Config persistence SONiC VS does not auto-save. Always run config save -y before snapshot or reboot. No hardware offload VS dataplane is pure software. ACLs and QoS work logically. Don't benchmark throughput. Default credentials changed 202311+: admin / YourPaSsWoRd Older builds: admin / admin Docker startup time All containers take ~60–90 s to come up. Run docker ps and wait for all to show Up. QEMU adapter type virtio only — set during template creation. e1000 breaks interface mapping completely. splithorizon SONiC on GNS3 — getting started · SONiC 202311 · GNS3 2.2.x Paul Carvill · CCIE #16661 Emeritus · splithorizon.io