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7f551081adcbbf700b594ea733c02d4cea10434a
lab/labsim/sim-net-config.py
Michal 7f551081ad labsim: capture BGP, dual WAN and both ISP VMs as code 
The sim's routing config existed only as running state on the VMs. It was
applied by hand over SSH, so rebuilding a VM lost the rehearsal and nothing
recorded why any of it was shaped the way it was. The two ISP VMs were not
referenced anywhere in the repo at all.

sim-net-config.py generates all four roles; sim-net-apply.sh applies them over
the serial console, or diffs them against the running VMs. Verified reproducing
live state exactly before committing: primary 40/40 commands, secondary 16/16,
isp-dhcp 19/19, isp-pppoe 21/21.

Carries the reasoning that was previously nowhere: RFC 8212 needing policy in
both directions or the session carries zero prefixes; probe targets that must
not double as system name-servers; default-route-distance 210 rather than
no-default-route, which blanks new_routers and hands the default route to the
backup line; and the WI-8 bootstrap bug that pinned /32s fix.

Dropped a stale `pppoe-server interface eth0` on isp-pppoe (a NIC that does not
exist there) so a green drift check stays meaningful.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DMVzWZgiKW2wquf5z8S1yH
2026-08-22 16:26:36 +01:00

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#!/usr/bin/env python3
"""Generate the labsim routing + WAN config: BGP, dual WAN, and the two ISP VMs.
`sim-ha-config.py` covers the LAN side of the sim routers (addresses, VRRP,
conntrack-sync, DHCP). This covers everything that makes the sim a rehearsal for
production routing rather than just a LAN:
* eBGP between the sim routers and the k3s nodes, carrying the service range
* dual WAN -- DHCP on VLAN 53, PPPoE on VLAN 51 -- with health-checked failover
* the two ISP VMs that terminate those WANs and NAT to the real internet
All of it previously existed only as running state on the VMs, applied by hand
over SSH. Rebuilding a VM lost the rehearsal, and nothing recorded *why* any of
it was shaped the way it is. That is the entire reason this file exists.
./sim-net-config.py --role primary > r1-net.conf
./console-apply.py --vm labsim-vyos --config r1-net.conf
or apply all four at once with ./sim-net-apply.sh.
"""
from __future__ import annotations
import argparse
import sys
# ---------------------------------------------------------------------------
# BGP. Numbers match production so what is proven here ports over unchanged.
# ---------------------------------------------------------------------------
ROUTER_AS = 65000
CLUSTER_AS = 65001
# The service range Cilium advertises. Chosen against a survey of third-party
# RFC1918 defaults (docker-desktop, tailscale, k3s, EKS...) so it cannot collide
# with something we adopt later. Production uses the same /22 -- keep them equal.
SERVICE_CIDR = "10.61.0.0/22"
K8S_VLAN = 2
K8S_NODES = ["172.31.2.11", "172.31.2.12", "172.31.2.13"]
PEER_GROUP = "K8S"
PFX_LIST = "K8S-SERVICE-IPS"
RM_IN, RM_OUT = "K8S-IN", "K8S-OUT"
# One route per node; ECMP across all three. 4 leaves headroom for a fourth node
# without a config change.
MAX_PATHS = 4
# A safety valve, not a capacity plan: a misconfigured Cilium that starts
# advertising pod CIDRs should tear the session down, not quietly fill the FIB.
MAX_PREFIX = 100
# ---------------------------------------------------------------------------
# Dual WAN. The sim ISPs deliberately use TEST-NET-3 (203.0.113.0/24) and
# TEST-NET-2 (198.51.100.0/24) from RFC 5737: documentation ranges that are
# guaranteed never to be real destinations, so a leaked sim route cannot
# blackhole something that matters.
# ---------------------------------------------------------------------------
WAN_DHCP_VLAN = 53 # "10gig-equivalent" -- the primary in production
WAN_PPPOE_VLAN = 51 # "Vodafone-equivalent" -- the backup
ISP_DHCP_NET = "203.0.113.0/24"
ISP_DHCP_GW = "203.0.113.1"
ISP_DHCP_POOL = ("203.0.113.100", "203.0.113.150")
ISP_PPPOE_NET = "198.51.100.0/24"
ISP_PPPOE_GW = "198.51.100.1"
ISP_PPPOE_POOL = ("198.51.100.100", "198.51.100.150")
# Sim-only fake credentials. Both ends are in this file on purpose: they
# authenticate nothing real, and splitting them across a secret store would make
# the sim unreproducible for no security gain. The PRODUCTION PPPoE password
# lives in /config/wan-secrets on the router and is never in git.
PPPOE_USER, PPPOE_PASS = "simdsl", "simpass"
PPPOE_MTU = 1492 # 1500 - 8 bytes of PPPoE header
PPPOE_AC = "sim-isp"
# Failover probe targets. NOT 8.8.8.8/8.8.4.4: those are `system name-server`,
# so a probe failure and a DNS failure would be the same event and the router
# would flap the WAN every time DNS hiccuped.
PROBE_TARGETS = ["9.9.9.9", "208.67.222.222"]
# The bug this shape fixes (WI-8, found here, fixed in production): `ping -I
# bond0.53` binds the SOURCE address but does not make the kernel use that
# interface's gateway. On a cold boot where PPPoE won the default route, probes
# for the 10 gig egressed via PPPoE, succeeded, and the 10 gig was still never
# selected -- the house ran on the backup line silently. Pinning each target as
# a /32 via `dhcp-interface` forces the probe onto the line being tested.
WAN_DHCP_DISTANCE = 210 # NOT `no-default-route`, which blanks new_routers
PPPOE_DISTANCE = 10 # in the lease file, leaving failover no gateway
# to install and silently handing the default
# route to the backup line.
SIM_LAN = "172.31.0.0/16"
# The sim routers' own libvirt-NAT uplink, from before the ISP VMs existed. It
# is a third default route that does not exist in production and quietly masks
# WAN failures during a failover test. `--drop-scaffold` removes it.
SCAFFOLD_IF = "eth2"
SCAFFOLD_NAT_RULE = 100
def bgp(role: str) -> list[str]:
"""eBGP toward the k3s nodes. Identical on both routers except router-id."""
octet = 252 if role == "primary" else 253
out = [
f"# --- BGP: AS{ROUTER_AS} <-> AS{CLUSTER_AS} (k3s/Cilium) ---",
# FRR enforces RFC 8212: an eBGP session with no policy establishes but
# exchanges ZERO prefixes, silently. Both directions need a policy or
# the session looks perfectly healthy and carries nothing.
f"set policy prefix-list {PFX_LIST} rule 10 action permit",
f"set policy prefix-list {PFX_LIST} rule 10 prefix {SERVICE_CIDR}",
# `le 32` because Cilium advertises individual /32 service addresses out
# of the pool, not the aggregate.
f"set policy prefix-list {PFX_LIST} rule 10 le 32",
f"set policy route-map {RM_IN} rule 10 action permit",
f"set policy route-map {RM_IN} rule 10 match ip address prefix-list {PFX_LIST}",
# Deny everything outbound. The cluster must never learn a default route
# from us -- Cilium would install it and blackhole pod egress.
f"set policy route-map {RM_OUT} rule 10 action deny",
f"set protocols bgp system-as {ROUTER_AS}",
f"set protocols bgp parameters router-id 172.31.{K8S_VLAN}.{octet}",
f"set protocols bgp address-family ipv4-unicast maximum-paths ebgp {MAX_PATHS}",
f"set protocols bgp peer-group {PEER_GROUP} remote-as {CLUSTER_AS}",
f"set protocols bgp peer-group {PEER_GROUP} address-family ipv4-unicast route-map import {RM_IN}",
f"set protocols bgp peer-group {PEER_GROUP} address-family ipv4-unicast route-map export {RM_OUT}",
f"set protocols bgp peer-group {PEER_GROUP} address-family ipv4-unicast maximum-prefix {MAX_PREFIX}",
]
out += [f"set protocols bgp neighbor {n} peer-group {PEER_GROUP}" for n in K8S_NODES]
out.append("")
return out
def wan(drop_scaffold: bool) -> list[str]:
"""Dual WAN + health-checked failover. Primary router only -- see README."""
out = [
"# --- WAN: DHCP (primary) + PPPoE (backup), health-checked ---",
f"set interfaces bonding bond0 vif {WAN_PPPOE_VLAN} description "
f"'WAN1 Vodafone-equivalent (sim ISP PPPoE)'",
f"set interfaces bonding bond0 vif {WAN_DHCP_VLAN} address dhcp",
f"set interfaces bonding bond0 vif {WAN_DHCP_VLAN} description "
f"'WAN3 10gig-equivalent (sim ISP DHCP)'",
f"set interfaces bonding bond0 vif {WAN_DHCP_VLAN} dhcp-options "
f"default-route-distance {WAN_DHCP_DISTANCE}",
f"set interfaces pppoe pppoe0 source-interface bond0.{WAN_PPPOE_VLAN}",
f"set interfaces pppoe pppoe0 authentication username {PPPOE_USER}",
f"set interfaces pppoe pppoe0 authentication password {PPPOE_PASS}",
f"set interfaces pppoe pppoe0 default-route-distance {PPPOE_DISTANCE}",
f"set interfaces pppoe pppoe0 mtu {PPPOE_MTU}",
# The ISP's resolvers would otherwise overwrite ours in resolv.conf every
# time the session comes up.
"set interfaces pppoe pppoe0 no-peer-dns",
"",
"# Failover: prefer the DHCP WAN, fall back to PPPoE when probes fail.",
f"set protocols failover route 0.0.0.0/0 dhcp-interface bond0.{WAN_DHCP_VLAN} metric 1",
f"set protocols failover route 0.0.0.0/0 dhcp-interface bond0.{WAN_DHCP_VLAN} check type icmp",
f"set protocols failover route 0.0.0.0/0 dhcp-interface bond0.{WAN_DHCP_VLAN} check timeout 5",
# any-available, not all: one unreachable public resolver is a normal
# internet event, not a reason to abandon a working 10 gig line.
f"set protocols failover route 0.0.0.0/0 dhcp-interface bond0.{WAN_DHCP_VLAN} check policy any-available",
]
for t in PROBE_TARGETS:
out.append(f"set protocols failover route 0.0.0.0/0 dhcp-interface "
f"bond0.{WAN_DHCP_VLAN} check target {t}")
out.append("")
out.append("# Pin the probe targets to the line under test (WI-8 -- see above).")
for t in PROBE_TARGETS:
out.append(f"set protocols static route {t}/32 dhcp-interface bond0.{WAN_DHCP_VLAN}")
out += [
"",
"# Masquerade out of whichever WAN currently holds the default route.",
f"set nat source rule 110 outbound-interface name bond0.{WAN_DHCP_VLAN}",
f"set nat source rule 110 source address {SIM_LAN}",
"set nat source rule 110 translation address masquerade",
"set nat source rule 120 outbound-interface name pppoe0",
f"set nat source rule 120 source address {SIM_LAN}",
"set nat source rule 120 translation address masquerade",
"",
]
if drop_scaffold:
out += [
"# Remove the pre-ISP-VM libvirt-NAT uplink: a third default route",
"# that has no production equivalent and hides real WAN failures.",
f"delete interfaces ethernet {SCAFFOLD_IF} address",
f"delete nat source rule {SCAFFOLD_NAT_RULE}",
"",
]
return out
def isp_dhcp(wan_if: str, uplink_if: str) -> list[str]:
"""The 10gig-equivalent ISP: hands out a lease, NATs to the real internet."""
return [
f"# --- sim ISP: DHCP WAN on VLAN {WAN_DHCP_VLAN} ---",
"set system host-name isp-dhcp",
f"set interfaces ethernet {wan_if} address {ISP_DHCP_GW}/24",
f"set interfaces ethernet {wan_if} description "
f"'sim ISP - 10gig-equivalent WAN on VLAN{WAN_DHCP_VLAN}'",
f"set interfaces ethernet {uplink_if} address dhcp",
f"set interfaces ethernet {uplink_if} description 'uplink to the real internet'",
f"set service dhcp-server shared-network-name WAN{WAN_DHCP_VLAN} "
f"subnet {ISP_DHCP_NET} subnet-id 1",
f"set service dhcp-server shared-network-name WAN{WAN_DHCP_VLAN} "
f"subnet {ISP_DHCP_NET} option default-router {ISP_DHCP_GW}",
f"set service dhcp-server shared-network-name WAN{WAN_DHCP_VLAN} "
f"subnet {ISP_DHCP_NET} option name-server 8.8.8.8",
f"set service dhcp-server shared-network-name WAN{WAN_DHCP_VLAN} "
f"subnet {ISP_DHCP_NET} range CUST start {ISP_DHCP_POOL[0]}",
f"set service dhcp-server shared-network-name WAN{WAN_DHCP_VLAN} "
f"subnet {ISP_DHCP_NET} range CUST stop {ISP_DHCP_POOL[1]}",
"",
] + _isp_common(uplink_if, ISP_DHCP_NET, "sim ISP: NAT customers to the real internet")
def isp_pppoe(wan_if: str, uplink_if: str) -> list[str]:
"""The Vodafone-equivalent ISP: terminates PPPoE, NATs to the real internet."""
return [
f"# --- sim ISP: PPPoE WAN on VLAN {WAN_PPPOE_VLAN} ---",
"set system host-name isp-pppoe",
f"set interfaces ethernet {wan_if} description "
f"'sim ISP - Vodafone-equivalent WAN on VLAN{WAN_PPPOE_VLAN} (PPPoE)'",
f"set interfaces ethernet {uplink_if} address dhcp",
f"set interfaces ethernet {uplink_if} description 'uplink to the real internet'",
f"set service pppoe-server access-concentrator {PPPOE_AC}",
f"set service pppoe-server interface {wan_if}",
f"set service pppoe-server gateway-address {ISP_PPPOE_GW}",
"set service pppoe-server authentication mode local",
f"set service pppoe-server authentication local-users username {PPPOE_USER} "
f"password {PPPOE_PASS}",
f"set service pppoe-server client-ip-pool CUST range "
f"{ISP_PPPOE_POOL[0]}-{ISP_PPPOE_POOL[1]}",
"set service pppoe-server default-pool CUST",
"set service pppoe-server name-server 8.8.8.8",
"",
] + _isp_common(uplink_if, ISP_PPPOE_NET, "sim ISP: NAT PPPoE customers to the real internet")
def _isp_common(uplink_if: str, customer_net: str, desc: str) -> list[str]:
return [
"set nat source rule 100 description " + f"'{desc}'",
f"set nat source rule 100 outbound-interface name {uplink_if}",
f"set nat source rule 100 source address {customer_net}",
"set nat source rule 100 translation address masquerade",
"",
# An ISP that drops return traffic is not simulating an ISP. The forward
# chain defaults to accept here on purpose -- these VMs model the
# internet, and the thing under test is the router's firewall, not this.
"set firewall ipv4 forward filter default-action accept",
"set firewall ipv4 forward filter rule 10 action accept",
"set firewall ipv4 forward filter rule 10 state established",
"set firewall ipv4 forward filter rule 10 state related",
"set firewall ipv4 forward filter rule 10 description conntrack-engage",
"",
]
def build(role: str, drop_scaffold: bool, wan_if: str, uplink_if: str) -> list[str]:
if role == "primary":
# WAN lives on the primary only. Production has WAN on both routers;
# the sim does not, because two PPPoE clients sharing one credential
# against a single access concentrator is a different failure mode than
# anything production has. VRRP/conntrack failover is still exercised --
# see README, "known gaps".
return [f"# labsim routing -- {role}", ""] + bgp(role) + wan(drop_scaffold)
if role == "secondary":
return [f"# labsim routing -- {role}", ""] + bgp(role)
if role == "isp-dhcp":
return isp_dhcp(wan_if, uplink_if)
return isp_pppoe(wan_if, uplink_if)
def main() -> int:
ap = argparse.ArgumentParser()
ap.add_argument("--role", required=True,
choices=("primary", "secondary", "isp-dhcp", "isp-pppoe"))
ap.add_argument("--drop-scaffold", action="store_true",
help="also remove the pre-ISP-VM libvirt-NAT uplink (primary only)")
# The ISP VMs' interface names depend on PCI enumeration order, which is not
# stable across a rebuild: isp-dhcp came up as eth0/eth1 and isp-pppoe as
# eth2/eth3 from identical XML. Check with `show interfaces` before applying
# rather than trusting these defaults.
ap.add_argument("--wan-if", default=None, help="ISP VM: customer-facing NIC")
ap.add_argument("--uplink-if", default=None, help="ISP VM: internet-facing NIC")
args = ap.parse_args()
defaults = {"isp-dhcp": ("eth0", "eth1"), "isp-pppoe": ("eth2", "eth3")}
w, u = defaults.get(args.role, ("", ""))
w, u = args.wan_if or w, args.uplink_if or u
if args.drop_scaffold and args.role != "primary":
print("--drop-scaffold only applies to --role primary", file=sys.stderr)
return 2
lines = build(args.role, args.drop_scaffold, w, u)
sys.stdout.write("\n".join(lines) + "\n")
n = len([l for l in lines if l.startswith(("set ", "delete "))])
print(f"{args.role}: {n} commands", file=sys.stderr)
return 0
if __name__ == "__main__":
sys.exit(main())
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