When troubleshooting LDP operations on the Cisco IOS and IOS XE routers, what is one of the
first things that should be verified?
A.
if running OSPF as the IGP, ensure that OSPFv3 has been enabled
B.
check if the ip cef command has been enabled
C.
verify in the running configurations that all of the required LDP interfaces are defined under the
mpls ldp command configuration mode
D.
verify if there are any access lists that are denying TCP and UDP port 464 packets
Explanation:
http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fsldp22.html#wp1354836
An LSR engages in discovery by periodically transmitting LDP Hello messages to signal its desire to advertise label bindings. The LSR sends the LDP Hello messages as UDP packets to the well known LDP port (646).
LDP label distribution between two LSRs requires establishment of an LDP session. LSRs that have discovered each other establish an LDP session by:
•Opening a TCP connection to be used to distribute label bindings.
TCP port 646