What physical port does a SNMP trap/inform go out on?

Question

I would like a switch to let my server know of link status.

Does a trap/inform go out one or many ports?
What if the link sending the trap/inform goes down, how do I retrieve traps/informs?
Is this switch dependent, (e.g. dedicated management port or not)?

Ron Maupin · Accepted Answer · 2016-05-05 17:53:17Z

Just like any host, if the server is on the same network as the switch management interface, it gets switched to the correct port based on the MAC address of the destination, otherwise it gets sent to the configured gateway for the switch from the port which connects to the gateway, based on the gateway MAC address.
Just like any host, if the path to the destination is broken anywhere, the traps/informs don't reach the destination, and you don't get them.
Since a switch is a layer-2 device, and it is sending a layer-3 packet for SNMP, it needs to come from the layer-3 interface (usually a logical, management interface).

I am having a hard time grasping the idea of a "dedicated management port". An arista 7050t-36 has a dedicated port that I can talk out of band with from a client. A netgear m7100-24x does not (I believe), in the GUI interface I set up a management vlan. Does this mean every port on the switch is in that vlan and no matter what port I am, I can talk management? — user_ABCD
– user_ABCD, Commented May 5, 2016 at 18:39
Ports are in the VLAN you configure them to be. You can configure ports to be in the same VLAN as the switch management interface. The management interface is often a logical, rather than a physical interface. This is dependent on the vendor and switch model. For instance, Cisco switches can have a management interface on any, or all, VLANs within the switch; you just configure a layer-3 SVI and assign it an IP address. When the switch, itself, wants to send something on such a VLAN, it sources it from the SVI of that VLAN. — Ron Maupin
– Ron Maupin ♦, Commented May 5, 2016 at 18:44

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