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@jennifer/routeros

Neighbor discovery

File: src/topics/neighbor.j. Path: /ip/neighbor (NEIGHBOR_PATH).

Background

Network devices announce themselves on the wire - MikroTik with MNDP, Cisco with CDP, most vendors with LLDP. The router collects those announcements from its directly-connected segments, so /ip/neighbor answers "what is plugged into this segment" without a scan: the switch on ether2, the AP on ether5, the router upstream. Only same-segment neighbors appear - nothing behind another router.

Struct

jennifer
mt.Neighbor { interfaceName, address, mac, identity, platform, board, version }

Functions

FunctionPurpose
neighbors(c) → list of Neighboreverything discovered
neighborsOn(c, interfaceName)one interface's neighbors

Example

Map the rack:

jennifer
def ns as list of mt.Neighbor init mt.neighbors($c);
for (def n in $ns) {
    io.printf("%s: %s %s (%s) at %s on %s\n",
        $n.identity, $n.platform, $n.board, $n.version, $n.address, $n.interfaceName);
}

Find what's on the uplink:

jennifer
def up as list of mt.Neighbor init mt.neighborsOn($c, "ether1");
for (def n in $up) { io.printf("upstream: %s (%s)\n", $n.identity, $n.address); }

Pitfalls

  • Layer-2 only: a neighbor with no address was heard at layer 2 but has no IP on this segment - normal, not an error.
  • Discovery must be enabled on the interface for the router to hear (and be heard) - it is on by default, but a hardened config may restrict /ip/neighbor/discovery-settings (generic verbs); on an untrusted/WAN interface, turning discovery off is good hygiene (it otherwise leaks your model and version).
  • Non-announcing devices (plain PCs, most servers) never appear - absence here doesn't mean nothing is connected. Pair with arp.md for IP↔MAC presence.