LDP - Label distribution protocol

LDP is used to exchange labels used for IP forwarding. A separate protocol was chosen to minimize changes needed to IGPs.

LDP is a standard (RFS 3036) that replaced Cisco’s proprietary Tag Distribution Protocol (TDP)

Generally used on directly connected neighbors, can be targeted for routed neighbors.

frame-mode mpls - per-platform label space

224.0.0.2 All routers multicast address,

Hello packet UDP port 646 for source and destination

LSR ID: Highest IP on loopback interface

Highest LSR ID becomes active

TCP destination port 646 used for LDP session

show mpls ldp neighbor

clear mpls ldp neighbor 1.1.1.1

show mpls ldp discovery detail

Liberal Label Retention - keeps both upstream and downstream label

Label Switch Path - by default, same as IGP

1. Which LDP neighbors advertise network
2. Who owns next hop IPv4 for network

• RIB - Routing Information Base (All routes learned about)
• FIB - Forwarding Information Base (Routing Table)
• LIB - Label Information Base (All labels learned LDP)
• LFIB - Label Forwarding Information Base (Label Forwarding Table)
• CEF - Cisco Express Forwarding (cache of FIB and LFIB)

LFIB takes priority over FIB

!!RIB
show ip ospf 1 rib

!!FIB
show ip route

!!LIB
show mpls ldp bindings 

!!LFIB
show mpls forwarding-table

LDP Security

• Authentication
• LDP Session Protection
• IGP Synchronisation
• Label Filtering

LDP Authentication

Password set individually for each neighbour

mpls neighbor 1.1.1.1 password Password123!

MPLS LDP Lossless MD5 session authentication

access-list 10 permit host 1.1.1.1

key chain LDP_KEYS
	key 1
		key-string Password123!
		accept-lifetime 0:0:0 jan 1 2002 infinite
		send-lifetime 0:0:0 jan 1 2002 infinite
		
mpls ldp password option 2 for 10 key-chain LDP_KEYS
mpls ldp password required