Diagnostics
Three one-shot read-only checks that inspect the live network state: routing table, connectivity test and advanced statistics. None of them write to /etc/network/interfaces — safe to use at any time, including over SSH. For interactive live monitoring, see Live monitoring tools.
What this does
Show Routing Table
Lists every route the kernel currently uses (ip route show) and highlights the default gateway. Useful for confirming that traffic to the internet leaves through the expected interface and that no leftover routes are taking precedence.
Total routes: 4 ➡ default via 192.168.1.1 dev vmbr0 onlink • 10.10.10.0/24 dev vmbr1 proto kernel scope link src 10.10.10.1 • 169.254.0.0/16 dev vmbr0 scope link metric 1000 • 192.168.1.0/24 dev vmbr0 proto kernel scope link src 192.168.1.10 🌍 Default Gateway: 192.168.1.1
Test Connectivity
Sends two ICMP probes to three targets in sequence and reports each one. Then runs an nslookup google.com to verify DNS resolution independently of ICMP.
| Test | Target | What it confirms |
|---|---|---|
| Google DNS | 8.8.8.8 | External reachability via well-known anycast IP |
| Cloudflare DNS | 1.1.1.1 | Independent second-opinion if Google blocks ICMP |
| Gateway | (default route) | L2 / L3 connectivity to the local router |
| DNS Resolution | google.com | DNS server is reachable and answering |
Reading the result
8.8.8.8 succeed, the issue is the resolver, not the network: check /etc/resolv.conf.Advanced Diagnostics
Aggregates network-wide statistics and runs a battery of common-issue checks. Reports active connection counts, listening ports, total interfaces and flags two anti-patterns explicitly:
- NetworkManager running on a Proxmox host. NetworkManager and Proxmox's
ifupdownconflict — both try to manage interfaces, leading to bridges that flap or refuse to come up. If detected, the tool offers an interactive prompt to stop, disable and purge it (this is the only diagnostic that can modify the system, and only after explicit consent). - Duplicate IP addresses on different interfaces. Two interfaces holding the same IPv4 cause intermittent connectivity that's extremely hard to debug from inside the VM. Detected via
ip -4 addr show | sort | uniq -d.
The NetworkManager prompt is the only modifying action here
systemctl stop / disable + apt-get purge -y network-manager. If you decline, nothing changes.Troubleshooting
Test Connectivity reports the gateway as failed but the host has internet
traceroute 8.8.8.8 from a console: if the second hop is your ISP and the public DNS test passed, the gateway is fine despite the failed ping.Advanced Diagnostics keeps flagging duplicate IPs after I removed one
ip -4 addr show to confirm; if the duplicate is still present, an interface is still holding it. Use ip addr del <IP>/<mask> dev <iface> to remove it from the live state, then edit /etc/network/interfaces if it is also persistent.Related
- Live monitoring tools — interactive iftop / iptraf-ng / iperf3 launchers.
- Bridge analysis & guided repair — when a vmbrX is missing its physical port.
- Config analysis & guided cleanup — when an old NIC is still declared but no longer present.
- Interfaces backup & restart — to snapshot the config before any change.