Hi friend!
The Link Layer Discovery Protocol (LLDP) is a standard Layer 2 topology discovery protocol defined in IEEE 802.1ab. LLDP allows a device to send local management information such as management IP address, device ID, and port ID to neighbors. LLDP provides a standard link-layer discovery method. Layer 2 information obtained through LLDP allows the NMS (Network Management System) to detect the topology of neighboring devices. Details, such as device capabilities or device identity can be advertised using this protocol.
Using LLDP, device information such as chassis identification, port ID, port description, system name and description, device capability (as router, switch, hub…), IP/MAC address, etc., are transmitted to the neighboring devices. This information is also stored in local Management Information Databases (MIBs), and can be queried with the Simple Network Management Protocol (SNMP). The LLDP-enabled devices have an LLDP agent installed in them, which sends out advertisements from all physical interfaces either periodically or as changes occur.
Network monitoring software (like WhatsUp Gold) uses SNMP queries to scan a device’s MIB to retrieve neighbor information. Plus its built-in layer 2/3 network discovery and mapping uses LLDP in conjunction with its ARP Cache Discovery method, as well as other layer 2/3 protocols, to trawl through the interconnected devices, retrieving information to build a detailed topology map. As LLDP works purely at the data link layer, WhatsUp Gold will discover devices with no recent IP traffic, as well as devices in a blocked state.
The Label Distribution Protocol (LDP) is used to establish MPLS transport LSPs when traffic engineering is not required. It establishes LSPs that follow the existing IP routing table, and is particularly well suited for establishing a full mesh of LSPs between all of the routers on the network.
LDP can operate in many modes to suit different requirements; however the most common usage is unsolicited mode, which sets up a full mesh of tunnels between routers.
In solicited mode, the ingress router sends an LDP label request to the next hop router, as determined from its IP routing table. This request is forwarded on through the network hop-by-hop by each router. Once the request reaches the egress router, a return message is generated. This message confirms the LSP and tells each router the label mapping to use on each link for that LSP.
In unsolicited mode, the egress routers broadcast label mappings for each external link to all of their neighbors. These broadcasts are fanned across every link through the network until they reach the ingress routers. Across each hop, they inform the upstream router of the label mapping to use for each external link, and by flooding the network they establish LSPs between all of the external links.
The main advantage of LDP over RSVP is the ease of setting up a full mesh of tunnels using unsolicited mode, so it is most often used in this mode to set up the underlying mesh of tunnels needed by Layer 2 and Layer 3 VPNs.
Hope to help you!
