LLDP query – Why is LLDP supported on routers

Media Endpoint Discovery is an enhancement of LLDP, known as LLDP-MED, that provides the following facilities:

• Auto-discovery of LAN policies (such as VLAN, Layer 2 Priority and Differentiated services (Diffserv) settings) enabling plug and play networking.
• Device location discovery to allow creation of location databases and, in the case of Voice over Internet Protocol (VoIP), Enhanced 911 services.
• Extended and automated power management of Power over Ethernet (PoE) end points.
• Inventory management, allowing network administrators to track their network devices, and determine their characteristics (manufacturer, software and hardware versions, serial or asset number).

The LLDP-MED protocol extension was formally approved and published as the standard ANSI/TIA-1057 by the Telecommunications Industry Association (TIA) in April 2006.

It depends on the hardware involved. Juniper for example will drop the LLDP packets when there is no native VLAN configured (a VLAN in which all untagged traffic will be forwarded in).

Cisco for example will always send the LLDP tagged in VLAN 1. Juniper itself sends the LLDP untagged.

So it highly depends on your gear.