Network troubleshooting

Ordered triage

oc> lspci              (NIC on the bus?)
oc> ifconfig           (driver bound? MAC present?)
oc> nicstat            (counters moving?)
oc> dhcp               (address + gateway + DNS)
oc> ping 10.0.2.2      (ICMP to the QEMU gateway)
oc> arp                (L2 resolution happened?)
oc> dns example.com    (UDP + resolver OK?)
oc> wget 10.0.2.2      (full TCP + HTTP round trip)

Each step isolates a layer: bus -> driver -> L2 -> L3 -> L4 -> application.

QEMU specifics

• User-mode networking always provides 10.0.2.2 (gateway) and DNS forwarding - no host configuration needed.
• The default -device e1000 is the best-tested path.
• Two-instance tests: shared -netdev socket/multicast gives a real two-node link for the NIC tests.

TLS/SSH specifics

• Certificate failures print the exact verification stage (chain/hostname/policy) - read the message; the trust model (un-anchored warns, mismatch is fatal for named hosts) is in arch/network-stack.md.
• sshd needs the /etc volume seeded (host_keygen_etc) - the E2E suite's prerequisite.