Dec
07

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.

mpls-ine-blog

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”

 
  1. Mark Lah says:

    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.

  2. mbahar says:

    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.

  3. sergio says:

    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.

  4. oliv says:

    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

  5. oliv says:

    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

  6. oliv says:

    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

  7. Nicolas says:

    LDP is not enabled on R3 (might not even be on R2&R4). No LDP neighbor -> No remote label -> No forwarding.

  8. FrozenEyes says:

    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 .

  9. 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 :)

  10. Basile says:

    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 :-)

  11. Peter Koltl, CCIE #10192 says:

    R3 Lo0 is not routed. LDP sessions can’t be built as they use loopback addresses.

    R3
    interface Loopback0
    ip ospf 254 area 0

  12. AJN says:

    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)

  13. Steve says:

    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.

  14. diriger says:

    ip cef ?

  15. Gaurav Singla says:

    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.

  16. Mbong says:

    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.

  17. Mbong says:

    use the mpls ldp discovery transport-address interface interface configuration mode command.

  18. 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!

  19. somebody says:

    why You cannot paste “sh run”
    from every router
    On exam You have access to all command and devices.
    It’s sick

  20. Bob says:

    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?

  21. hpsn says:

    As a lot of people have mentioned.

    R3 loopback ip address is not being advertised to R2 and R4.

  22. Bob- That wasn’t intentional, and great job of identifying it. Thanks.

  23. [...] had also improved his skills in MPLS, Multi-Protocol BGP, IOS IPS, EEM, and many other areas by using the sweet blog articles at INE.  [...]

  24. davy says:

    Great exercise!

  25. Vijaya Laxmi says:

    gr8 task!

 

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