Well, this is kinda funny. Firstly, I should mention that this is a project that I was recently asked to work on where everyone that previously worked on it has left the company and there is next to no documentation. All I had to go on was a grossly inaccurate network topology diagram which I am in the process of redrawing.
Anyway, after investigating a million other things, I traced the tremendous mess of cables behind the server racks to look at the multiple ethernet cables from the segment that wasn't talking to the rest of the network. This is where I saw no link lights for the ethernet ports on the back of a server whereas the front panel showed several green lights. What I found out is that the front panel of the server will show those green lights even when it isn't turned on! Since it was off, there was no active connection from that particular server rack to the rest of the network. After turning it on, I checked the router again and AREA 0 is no longer inactive. It now has its OSPF neighbors and routes that it should have and the end devices are able to communicate properly. So, everything works now that the server has been turned on.
In summary, one needs to always ask the following two questions:
- Are you sure it's plugged in?
- Have you tried turning it off and on again?
First, I would recommend checking out Cisco's MPLS FAQ For Beginners, or the NANOG Presentation "MPLS for Dummies" by Richard A Steenbergen. They both have some really good information.
With that said, let me address your questions one at a time. (I have excerpted them in part below.)
1: After the initial convergence of the network, LSPs now exist between all FECs which are typically interfaces on LERs that connect to a subnet.
Yes, LSP's exist towards all reachable FECs. And an MPLS packet could now be switched across the network.
2: Assuming that baseline is correct; How does R1 know it is an LER for an LSP that spans to R6 for example
R1 has no clue that it is part of an LSP that spans to R6. It only cares about the local/connected labels and FECs. That is part of what makes MPLS Label Switching fast and effective. It doesn't have to know the whole path. The router just knows that to reach FEC1, I apply label 1234, and exit interface XYZ.
Then later hops in the path utilize the same process, swapping in the appropriate next hop label and switching the packet on.
As for the bottom line question How are the LERs determined?, a router itself doesn't really know or care if it's an LER. It just knows that when it receives a packet destined for a local destination, with no tag, it delivers it.
In your output above, you can see that the first 4 outgoing FECs have Pop tag listed as the Outgoing Tag. A packet leaving R1 for one of the local subnets on R2 or R3 simply has it's tag popped and forwarded out the appropriate interface.
When R2 or R3 receive that packet, they see no label and process it via the normal routing process which delivers it to a local interface.
To quote the Wikipedia article on MPLS:
At the egress router, when the last label has been popped, only the payload remains. This can be an IP packet, or any of a number of other kinds of payload packet. The egress router must therefore have routing information for the packet's payload, since it must forward it without the help of label lookup tables. An MPLS transit router has no such requirement.
Best Answer
Did you try
no router ospf <process number>?That will delete the OSPF process. If you have created any interface specific OSPF configurations, you will need to deal with those individually.