Editing Label Distribution Protocol (section)

{{Short description|Computer network protocol}}
{{Infobox networking protocol
| title        = Label Distribution Protocol
| logo         = 
| logo alt     = 
| image        = 
| image alt    = 
| caption      = 
| is stack     = 
| abbreviation = LDP
| purpose      = 
| developer    =  
| date         = {{Start date and age|2007|10}}
| based on     = 
| influenced   = 
| osilayer     = 
| ports        = 646
| rfcs         = {{IETF RFC|5036}}
| hardware     = Routers
}}
'''Label Distribution Protocol''' ('''LDP''') is a [[protocol (computing)|protocol]] in which routers capable of [[Multiprotocol Label Switching]] (MPLS) exchange label mapping information. Two routers with an established session are called LDP peers and the exchange of information is bi-directional.
LDP is used to build and maintain [[label-switched path]] (LSP) databases that are used to forward traffic through MPLS networks.

LDP can be used to distribute the inner label (VC/VPN/service label) and outer label (path label) in MPLS. For inner label distribution, targeted LDP (tLDP) is used.

LDP and tLDP discovery runs on UDP port 646 and the session is built on TCP port 646. During the discovery phase hello packets are sent on UDP port 646 to the 'all routers on this subnet' group multicast address (224.0.0.2). However, tLDP unicasts the hello packets to the targeted neighbor's address.