Resolving MPLS LDP Troubleshooting Issue

When faced with a troubleshooting ticket involving MPLS you need to clear the basics first to ensure that everything is working from a Label Distribution perspective.

1. First of all you need to establish IGP connectivity between all the routers. 
2. Can you ping all the loopbacks?
3. Are there /32 loopbacks configured on every router and advertised into IGP?
4. Is CEF enabled?
5. Is MPLS IP enabled on the required interfaces?
6. Have the routers discovered any LDP neighbors?

I have put together this quick list of commands that I would run on each router to quickly verify that Label Distribution is working

sh run | inc ip cef
sh run | inc mpls ip
sh mpls interface
sh mpls ldp disco
sh mpls ldp neigh

And also when applied to a router in a working MPLS Core the output must look as per fig. below,