Tutorial 9 of 9
Network evidence — routes, address plans and tunnel MTU
Intermediate 8 min
Paste a routing table, an address plan or a tunnel stack, let the Signalhouse network tools find blackholes, overlapping subnets and MTU drops, and track them as Opsdeck findings.
Press Add evidence and paste network text. Three kinds send it to the Signalhouse Network lab tools (they belong to Signalhouse; Opsdeck runs them like its other tools):
| Kind | You paste | Tool | What becomes a finding |
|---|---|---|---|
| Routing table | ip route / ip -6 route output, rows like 10.0.0.0/8 192.0.2.1 eth1 ospf 110 20, or a topology exported from the Network lab | Signalhouse Route Lookup | destinations without a route, discard-route hits, routes that stop working, forwarding loops, MTU drops and asymmetric return paths |
| Address plan | prefixes, one per line, with an optional name | Signalhouse Subnet Planner | overlapping and duplicate subnets, addresses the summary route adds |
| Tunnel MTU | the encapsulations from the wire inwards, for example pppoe, wireguard, optionally mtu 9000, packet 1500 and df | Signalhouse MTU Calculator | packets that are dropped or fragmented, IPv6 below 1280 bytes |
Opsdeck recognises all three while you paste (This looks like a routing table or a Network lab topology.). Masking is off for them by default, because addresses are the evidence.
1. A routing table
Paste five ip route lines with an OSPF route 10.0.0.0/8, a static 10.20.0.0/16, blackhole 192.168.64.0/19 and two connected networks, but no default route. A routing table needs Destinations to look up: enter 10.1.2.3 10.20.5.9 192.168.70.1 8.8.8.8 and press Run. The result reads 4 destinations looked up in 5 installed prefixes: 3 matched, 1 without a route. Two findings follow: No route to 8.8.8.8: packets are dropped (ICMP destination unreachable). (High) and 192.168.70.1 matches the discard route 192.168.64.0/19: packets are dropped on purpose. (Medium). Interfaces that are down (optional) tests a failure, for example eth1. For a Network lab topology, fill in Topology: packet from (device), Topology: packet to (address or device) and the packet size instead; the metrics then show hops, forwarding loops and the path MTU.
2. An address plan
Paste 10.0.0.0/22 Office, 10.0.4.0/24 Lab, 10.0.4.128/25 Printers, 10.0.6.0/24 Guest Wi-Fi and 10.0.0.0/22 VPN pool. Opsdeck reports 10.0.4.128/25 (Printers) overlaps 10.0.4.0/24 (Lab): the addresses of the smaller subnet are assigned twice. (High), the duplicate 10.0.0.0/22 (Medium) and that the summary route 10.0.0.0/21 also covers 512 addresses outside the plan (Low).
3. A tunnel MTU
Paste pppoe, wireguard, packet 1500 and df. With the default Link MTU (bytes) of 1500 the key metrics show an Inner MTU of 1,432 bytes, 68 bytes of overhead and a TCP MSS of 1,392 bytes, and the High finding reads 1500-byte packets are dropped: the inner MTU of PPPoE (DSL) → WireGuard over IPv4 is 1432 bytes. Change Inner IP version to IPv6 to check an IPv6 tunnel.
4. Findings, gate and actions
Network findings work like all others: they appear under Findings, release-gate rules can use their key metrics (for example Destinations without a route or Overlapping subnet pairs), and Create action turns them into tasks.
To paste and mask other evidence see Paste evidence and mask secrets.
Ready to try it?