Same guard the ethernet-switch scenario already carries: NetworkManager
can release an NM-managed TAP from its bridge shortly after
(re-)enslavement (docs/bugs/networkmanager-tap-release.md). Applied to
the Dynamips, QEMU, IOU, IOL-runner and switch-cascade scenarios after
their nodes have booted (no-op where nmcli/NetworkManager is absent).
This keeps those tests deterministic on un-declared hosts.
The L2-anchor spec's behavioral guarantee — an idle link stays silent for
5 s once the enslavement burst settles — only ran in the Dynamips and
Docker suites. It now also runs in QEMU, IOU, the IOL container, the
switch fast path and the switch cascade, which covers every host-device
creation path:
* tap create (Dynamips/QEMU/IOU anchors), docker create_veth (Docker host
ends; the cascade's race-loser end is hardened after create by the
server), bridge add_nio_tap (the IOL container anchor, the fifth
creator), and the brctl switch bridges, whose multicast snooping is off
precisely so the bridge role can reach silence;
* each scenario silences its guests first (IOS interfaces shut through
the console; Docker guests' links down) and re-verifies the ping after;
* the cascade measures 8 devices at once (four absorbed router anchors,
both cascade ends, both switch bridges).
IOL 158 s, cascade 293 s, ESW fast path 378 s, QEMU 428 s, IOU 308 s —
all green.
Two switches cascaded through the link-owned veth pair, two c7200
routers per switch, real ICMP crossing both bridges: the pair is born
UP with exactly one end per switch bridge, a dot1q trunk cascade
carries two VLANs at once, the symmetric access/trunk mode flip on the
cascade ends isolates and revives a VLAN in place (asymmetric flips are
semantically broken — the access side egresses untagged into the far
trunk's native PVID), a delay filter lands as netem on both ends (one
per direction, RTT ~= 2x delay), suspend admin-downs both ends, and a
link delete/re-create retires the whole pair and mints a new one under
the new link id — zero host residue after the project goes.
