Cheers from London! I learned this week that a “Christmas Cracker” is not a food item, OR a person. 
There is so much to know. I am grateful for students willing to show me the ropes here in the UK. Thank you all. Now on to the topic at hand.
MPLS is an important part of the RS Bootcamp, including troubleshooting MPLS.
Here is an MPLS troubleshooting scenario, that has 1 (one,одну,un,uno) configuration issue. Can you spot it? Lets get to it! Here is the diagram.
Problem: Clients on the 5.5.5.0 network are not able to ping the server, or any other devices, on the 1.1.1.0 network. Your challenge, based on the provided IOS show commands only, is to identify the 1 configuration problem that is causing the network failure.
For this scenario, the PC and Server configurations are correct, as well as all the layer 2 switching infrastructure on the Catalyst switches. R1 and R5 are CE routers, R2 and R4 are PE routers, and R3 is a P router.
We will work from the diagram, using the show commands from right to left, starting with R5. (I have grouped the show commands together, then the individual commands and their output. This way, the post may be used as a study/reference tool.)
R5
show ip int brief | ex una
show ip route
show ip protocols
ping 136.1.45.255
R5#show ip int brief | ex una
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 5.5.5.5 YES manual up up
FastEthernet0/1 136.1.45.5 YES NVRAM up up
Loopback0 150.1.5.5 YES NVRAM up up
R5#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
136.1.0.0/24 is subnetted, 2 subnets
R 136.1.12.0 [120/1] via 136.1.45.4, 00:00:08, FastEthernet0/1
C 136.1.45.0 is directly connected, FastEthernet0/1
1.0.0.0/24 is subnetted, 1 subnets
R 1.1.1.0 [120/1] via 136.1.45.4, 00:00:08, FastEthernet0/1
5.0.0.0/24 is subnetted, 1 subnets
C 5.5.5.0 is directly connected, FastEthernet0/0
150.1.0.0/24 is subnetted, 1 subnets
C 150.1.5.0 is directly connected, Loopback0
R5#show ip protocols
Routing Protocol is "rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Sending updates every 30 seconds, next due in 11 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Redistributing: rip
Default version control: send version 2, receive version 2
Interface Send Recv Triggered RIP Key-chain
FastEthernet0/0 2 2
FastEthernet0/1 2 2
Automatic network summarization is not in effect
Maximum path: 4
Routing for Networks:
5.0.0.0
136.1.0.0
Routing Information Sources:
Gateway Distance Last Update
136.1.45.4 120 00:00:08
Distance: (default is 120)
R5#ping 136.1.45.255
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 136.1.45.255, timeout is 2 seconds:
Reply to request 0 from 136.1.45.4, 8 ms
Reply to request 1 from 136.1.45.4, 32 ms
Reply to request 2 from 136.1.45.4, 16 ms
Reply to request 3 from 136.1.45.4, 4 ms
Reply to request 4 from 136.1.45.4, 24 ms
R5#
R4
show ip route
show ip route vrf Vrf1
show ip protocols
show mpls interface
show mpls ldp neighbor
show mpls forwarding-table
show ip bgp summary
show ip bgp vpnv4 all
ping vrf Vrf1 136.1.45.255
ping 136.1.34.255
R4#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
136.1.0.0/24 is subnetted, 2 subnets
O 136.1.23.0 [110/65] via 136.1.34.3, 00:04:28, FastEthernet0/0
C 136.1.34.0 is directly connected, FastEthernet0/0
150.1.0.0/32 is subnetted, 2 subnets
C 150.1.4.4 is directly connected, Loopback0
O 150.1.2.2 [110/66] via 136.1.34.3, 00:04:28, FastEthernet0/0
R4#show ip route vrf Vrf1
Routing Table: Vrf1
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
136.1.0.0/24 is subnetted, 2 subnets
B 136.1.12.0 [200/0] via 150.1.2.2, 00:04:23
C 136.1.45.0 is directly connected, FastEthernet0/1
1.0.0.0/24 is subnetted, 1 subnets
B 1.1.1.0 [200/2] via 150.1.2.2, 00:04:23
5.0.0.0/24 is subnetted, 1 subnets
R 5.5.5.0 [120/1] via 136.1.45.5, 00:00:01, FastEthernet0/1
R4#show ip protocols
Routing Protocol is "ospf 234"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 150.1.4.4
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4
Routing for Networks:
Routing on Interfaces Configured Explicitly (Area 0):
FastEthernet0/0
Loopback0
Reference bandwidth unit is 100 mbps
Routing Information Sources:
Gateway Distance Last Update
150.1.2.2 110 00:04:28
150.1.3.3 110 00:04:28
Distance: (default is 110)
Routing Protocol is "rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Sending updates every 30 seconds, next due in 0 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Redistributing: rip
Default version control: send version 1, receive any version
Automatic network summarization is in effect
Maximum path: 4
Routing for Networks:
Routing Information Sources:
Gateway Distance Last Update
Distance: (default is 120)
Routing Protocol is "bgp 24"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
IGP synchronization is disabled
Automatic route summarization is disabled
Neighbor(s):
Address FiltIn FiltOut DistIn DistOut Weight RouteMap
150.1.2.2
Maximum path: 1
Routing Information Sources:
Gateway Distance Last Update
Distance: external 20 internal 200 local 200
R4#show mpls interface
Interface IP Tunnel Operational
FastEthernet0/0 Yes (ldp) No Yes
R4#show mpls ldp neighbor
R4#show mpls forwarding-table
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
17 Untagged 150.1.2.2/32 0 Fa0/0 136.1.34.3
18 Untagged 136.1.23.0/24 0 Fa0/0 136.1.34.3
19 Untagged 5.5.5.0/24[V] 19950 Fa0/1 136.1.45.5
20 Aggregate 136.1.45.0/24[V] 1684
R4#show ip bgp summary
BGP router identifier 150.1.4.4, local AS number 24
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
150.1.2.2 4 24 148 149 1 0 0 02:08:57 0
R4#show ip bgp vpnv4 all
BGP table version is 22, local router ID is 150.1.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf Vrf1)
*>i1.1.1.0/24 150.1.2.2 2 100 0 ?
*> 5.5.5.0/24 136.1.45.5 1 32768 ?
*>i136.1.12.0/24 150.1.2.2 0 100 0 ?
*> 136.1.45.0/24 0.0.0.0 0 32768 ?
R4#ping vrf Vrf1 136.1.45.255
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 136.1.45.255, timeout is 2 seconds:
Reply to request 0 from 136.1.45.5, 4 ms
Reply to request 1 from 136.1.45.5, 28 ms
Reply to request 2 from 136.1.45.5, 16 ms
Reply to request 3 from 136.1.45.5, 32 ms
Reply to request 4 from 136.1.45.5, 8 ms
R4#ping 136.1.34.255
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 136.1.34.255, timeout is 2 seconds:
Reply to request 0 from 136.1.34.3, 8 ms
Reply to request 1 from 136.1.34.3, 4 ms
Reply to request 2 from 136.1.34.3, 16 ms
Reply to request 3 from 136.1.34.3, 8 ms
Reply to request 4 from 136.1.34.3, 4 ms
R4#
R3
show ip route
show ip protocols
show mpls interface
show mpls ldp neighbor
show mpls forwarding-table
R3#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
136.1.0.0/24 is subnetted, 2 subnets
C 136.1.23.0 is directly connected, Serial0/0.23
C 136.1.34.0 is directly connected, FastEthernet0/0
150.1.0.0/32 is subnetted, 3 subnets
O 150.1.4.4 [110/2] via 136.1.34.4, 00:05:16, FastEthernet0/0
C 150.1.3.3 is directly connected, Loopback0
O 150.1.2.2 [110/65] via 136.1.23.2, 00:05:26, Serial0/0.23
R3#show ip protocols
Routing Protocol is "ospf 234"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 150.1.3.3
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4
Routing for Networks:
Routing on Interfaces Configured Explicitly (Area 0):
FastEthernet0/0
Serial0/0.23
Reference bandwidth unit is 100 mbps
Routing Information Sources:
Gateway Distance Last Update
150.1.4.4 110 00:05:16
150.1.2.2 110 00:05:26
Distance: (default is 110)
R3#show mpls interface
Interface IP Tunnel Operational
FastEthernet0/0 Yes (ldp) No Yes
Serial0/0.23 Yes (ldp) No Yes
R3#show mpls ldp neighbor
R3#show mpls forwarding-table
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 Untagged 150.1.2.2/32 0 Se0/0.23 point2point
17 Untagged 150.1.4.4/32 0 Fa0/0 136.1.34.4
R2
show ip route
show ip route vrf Vrf1
show ip protocols
show mpls interface
show mpls ldp neighbor
show mpls forwarding-table
show ip bgp summary
show ip bgp vpnv4 all
ping 136.1.23.255
ping vrf Vrf1 136.1.12.255
R2#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
136.1.0.0/24 is subnetted, 2 subnets
C 136.1.23.0 is directly connected, Serial0/0.23
O 136.1.34.0 [110/65] via 136.1.23.3, 00:05:41, Serial0/0.23
150.1.0.0/32 is subnetted, 2 subnets
O 150.1.4.4 [110/66] via 136.1.23.3, 00:05:41, Serial0/0.23
C 150.1.2.2 is directly connected, Loopback0
R2#show ip route vrf Vrf1
Routing Table: Vrf1
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
136.1.0.0/24 is subnetted, 2 subnets
C 136.1.12.0 is directly connected, FastEthernet0/0
B 136.1.45.0 [200/0] via 150.1.4.4, 00:05:18
1.0.0.0/24 is subnetted, 1 subnets
O 1.1.1.0 [110/2] via 136.1.12.1, 02:18:47, FastEthernet0/0
5.0.0.0/24 is subnetted, 1 subnets
B 5.5.5.0 [200/1] via 150.1.4.4, 00:05:18
R2#show ip protocols
Routing Protocol is "ospf 234"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 150.1.2.2
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4
Routing for Networks:
Routing on Interfaces Configured Explicitly (Area 0):
Serial0/0.23
Loopback0
Reference bandwidth unit is 100 mbps
Routing Information Sources:
Gateway Distance Last Update
150.1.4.4 110 00:05:41
150.1.3.3 110 00:05:51
Distance: (default is 110)
Routing Protocol is "bgp 24"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
IGP synchronization is disabled
Automatic route summarization is disabled
Neighbor(s):
Address FiltIn FiltOut DistIn DistOut Weight RouteMap
150.1.4.4
Maximum path: 1
Routing Information Sources:
Gateway Distance Last Update
Distance: external 20 internal 200 local 200
R2#show mpls interface
Interface IP Tunnel Operational
Serial0/0.23 Yes (ldp) No Yes
R2#show mpls ldp neighbor
R2#show mpls forwarding-table
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
17 Untagged 136.1.34.0/24 0 Se0/0.23 point2point
18 Untagged 150.1.4.4/32 0 Se0/0.23 point2point
21 Aggregate 136.1.12.0/24[V] 1040
22 Untagged 1.1.1.0/24[V] 18240 Fa0/0 136.1.12.1
R2#show ip bgp summary
BGP router identifier 150.1.2.2, local AS number 24
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
150.1.4.4 4 24 151 150 1 0 0 02:10:15 0
R2#show ip bgp vpnv4 all
BGP table version is 13, local router ID is 150.1.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
Route Distinguisher: 1:1 (default for vrf Vrf1)
*> 1.1.1.0/24 136.1.12.1 2 32768 ?
*>i5.5.5.0/24 150.1.4.4 1 100 0 ?
*> 136.1.12.0/24 0.0.0.0 0 32768 ?
*>i136.1.45.0/24 150.1.4.4 0 100 0 ?
R2#ping 136.1.23.255
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 136.1.23.255, timeout is 2 seconds:
Reply to request 0 from 136.1.23.3, 12 ms
Reply to request 1 from 136.1.23.3, 16 ms
Reply to request 2 from 136.1.23.3, 32 ms
Reply to request 3 from 136.1.23.3, 28 ms
Reply to request 4 from 136.1.23.3, 28 ms
R2#ping vrf Vrf1 136.1.12.255
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 136.1.12.255, timeout is 2 seconds:
Reply to request 0 from 136.1.12.1, 4 ms
Reply to request 1 from 136.1.12.1, 28 ms
Reply to request 2 from 136.1.12.1, 16 ms
Reply to request 3 from 136.1.12.1, 28 ms
Reply to request 4 from 136.1.12.1, 12 ms
R2#
R1
show ip int brief | ex una
show ip route
show ip protocols
ping 136.1.12.255
R1#show ip int brief | ex una
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 136.1.12.1 YES NVRAM up up
FastEthernet0/1 1.1.1.1 YES manual up up
Loopback0 150.1.1.1 YES NVRAM up up
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
136.1.0.0/24 is subnetted, 2 subnets
C 136.1.12.0 is directly connected, FastEthernet0/0
O E2 136.1.45.0 [110/1] via 136.1.12.2, 00:06:20, FastEthernet0/0
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, FastEthernet0/1
5.0.0.0/24 is subnetted, 1 subnets
O E2 5.5.5.0 [110/1] via 136.1.12.2, 00:06:20, FastEthernet0/0
150.1.0.0/24 is subnetted, 1 subnets
C 150.1.1.0 is directly connected, Loopback0
R1#show ip protocols
Routing Protocol is "ospf 12"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 150.1.1.1
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4
Routing for Networks:
1.1.1.0 0.0.0.255 area 0
136.1.12.1 0.0.0.0 area 0
Reference bandwidth unit is 100 mbps
Routing Information Sources:
Gateway Distance Last Update
136.1.12.2 110 00:06:20
Distance: (default is 110)
R1#ping 136.1.12.255
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 136.1.12.255, timeout is 2 seconds:
Reply to request 0 from 136.1.12.2, 8 ms
Reply to request 1 from 136.1.12.2, 20 ms
Reply to request 2 from 136.1.12.2, 12 ms
Reply to request 3 from 136.1.12.2, 24 ms
Reply to request 4 from 136.1.12.2, 8 ms
R1#
What do you see as the problem, and what may be done to correct it?
Good luck!
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25 Responses to ““Broken MPLS? Troubleshoot it we should, mmmmm.” … yoda”
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Looks to me like R3 isn’t advertising its Loopback0 address (150.1.3.3) into OSPF PID 234.
The solution to correct it would be to add that network statement into the OSPF 234 process on R3.
I can see that LDP peering does not form between R3 and R2/R4. Labels are not exchanged between the R2-R3-R4 LSR, thus R4 and R2 sees the outgoing “Untagged” labels towards R3 for all prefixes.
I believe the LDP peering failed because R2 and R4 does not have a route to R3′s loopback address, which is used for LDP peering. Including R3′s loopback interface under the OSPF process in R3 should resolve this.
It looks like R2 and R4 are not creating an LDP neighbor with R3. R3 needs to have its loopback in the IGP(OSPF), before this works.
R3 has no tag to BGP next hops 150.1.2.2 and 150.1.4.4, so when it receive a packet destined to 1.1.1.0/24 or 5.5.5.0/24 it just drop the packets as it has no routing infos to those networks in the global table
obvioulsy, ldp neighbor relationships between R4-R3 and R2-R2 are down. This could probably be because of router-id not reacheable.
the command “mpls ldp discovery transport-address interface” could help on transport interfaces between R4-R3 and R3-R2
olivier
Usually ldp, is a TCP session between loopbacks. In this case there is not loopback in the global table, this is why there is no end-to-end LSP.
Other option could be to add loopbacks in global table of R4,R3 and R2 and annouce them in OSPF. Then ldp sessions could occurs, and build LSPs.
Hope this helps
olivier
ooops, 150.1.2.2 and 150.1.4.4 are annouced, just missing to create 150.1.3.3 loopback in R3 and annouce it in OSPF…
olivier
LDP is not enabled on R3 (might not even be on R2&R4). No LDP neighbor -> No remote label -> No forwarding.
I think because Both PE and P router can’t form LDP neighbors between other and we can see that from show mpls ldp neighbor command .
Conclusion#1: iBGP next-hop has “untagged” outgoing label. Not good.
Conclusion#2: R2, R3 and R4 are not exchanging labels via LDP. Ahmm …
Conclusion#3: R3 has no LDP neighbors. Baaad.
Conclusion#4: loopback interface of R3 is not announced to R2 and R4, so the LDP session is not established. Fail.
Fix: change the LDP router ID or include loopback interface into the OSPF process.
Nice task
The loopback interface of R3 is not reachable from R4 and R2. Add net 150.1.3.3 0.0.0.0 a 0 under router ospf 234 on R3.
Bring us more MPLS questions
R3 Lo0 is not routed. LDP sessions can’t be built as they use loopback addresses.
R3
interface Loopback0
ip ospf 254 area 0
Observations:
- R4 sees .23.0 as “untagged” ==» not reachable through LDP (should be “POP tag”)
- R2 sees .34.0 as “untagged” ==» not reachable through LDP (should be “POP tag”)
- R4 do not receive 150.1.3.3 (R3 RID) through OSPF 234 ==» NOT advertised by R3
Consequently R3 do not establish LDP relationships with neither R2 nor R4
Solution:
- Better to hardcode Router-ID with “force” to avoid surprises (ex:better UP/UP loopback which is not advertised)
- LDP/MP-BGP RID should be unique & reachable (announced through backbone IGP)
R3 loopback is used for LDP peering.
R3 loopback is not advertised.
Can be fixed by advertising the loopback ip address as mentioned above.
Could also be fixed by using the transport address for the LDP TCP connection between neighbors
int fa0/0
mpls ldp discovery transport-address interface
int se0/0.23
mpls ldp discovery transport-address interface
A useful command for troubleshooting LDP peering is “show mpls ldp discovery” If ran on R2 or R4 it would show ” LDP Id: 150.1.3.3:0; no route”
Fun stuff.
ip cef ?
To form an LDP neighbor relationship, the remote LDP router-id should be reachable. Here R3 have chosen 150.1.3.3 as its LDP router-id. So to form an LDP neighborship, this ip 150.1.3.3 should be reachable from R2 and R4. That is missing from the ospf database.
It is simple…the transport address being used by MPLS LDP is not reachable from the neighbors. This can be displayed with the show mpls ldp discovery detail command.
use the mpls ldp discovery transport-address interface interface configuration mode command.
Excellent work people!!! The missing route to router’s 3 loopback was the problem, and thanks for the multiple solutions provided to fix it, or get around it. Also appreciated are the additional commands that would assist in pinpointing the problem even faster. Concise and accurate troubleshooting skills are a valuable asset in the troubleshooting and configuration sections of the CCIE 4 lab.
Again, thanks for all the responses, and good luck with your studies!
why You cannot paste “sh run”
from every router
On exam You have access to all command and devices.
It’s sick
Great brainteaser.
By the way, “R4#show mpls ldp neighbor” isn’t in bold like all the other commands. Is this intentional, since it’s a dead giveaway?
As a lot of people have mentioned.
R3 loopback ip address is not being advertised to R2 and R4.
Bob- That wasn’t intentional, and great job of identifying it. Thanks.
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Great exercise!
gr8 task!