Introduction to MPLS

Lessons Discussion
54

In the lesson CE <-> PE is BGP
PE <-> P is ospf

I tried to create a similar lab. I find that there is only a LSP if the router has a route for the destination.
So how does the P router have an LSP for 5.5.5.5 and 1.1.1.1 ?

PE1#show mpls forwarding-table 
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop    
Label      Label      or Tunnel Id     Switched      interface              
16         17         4.4.4.4/32       0             Gi0/2      192.168.23.3
17         Pop Label  192.168.34.0/24  0             Gi0/2      192.168.23.3
18         Pop Label  3.3.3.3/32       0             Gi0/2      192.168.23.3

There is no label rule for 5.5.5.5 so how do the packets get routed.
I read the page many times but I just don’t get it.

PE1 knows to send packets for 5.5.5.5 via 4.4.4.4
PE1 knows to get to 4.4.4.4 it has to send packets to 192.168.23.3

somehow MPLS gets involved in the decision. This is a recursive route. It is like MPLS is checked at each stage of the route recursion. Is that what happens or is it some sort of magic interaction between MPLS and iBGP ?

I tried to do the same thing with a static route

Gateway of last resort is not set

     1.0.0.0/32 is subnetted, 1 subnets
C       1.1.1.1 is directly connected, Loopback0
     2.0.0.0/32 is subnetted, 1 subnets
D       2.2.2.2 [90/409600] via 172.16.12.2, 00:00:57, FastEthernet0/0
     3.0.0.0/32 is subnetted, 1 subnets
D       3.3.3.3 [90/435200] via 172.16.12.2, 00:12:56, FastEthernet0/0
     4.0.0.0/32 is subnetted, 1 subnets
D       4.4.4.4 [90/437760] via 172.16.12.2, 00:12:56, FastEthernet0/0
     172.16.0.0/24 is subnetted, 3 subnets
D       172.16.34.0 [90/309760] via 172.16.12.2, 00:12:57, FastEthernet0/0
D       172.16.23.0 [90/307200] via 172.16.12.2, 00:19:16, FastEthernet0/0
C       172.16.12.0 is directly connected, FastEthernet0/0
C    192.168.1.0/24 is directly connected, FastEthernet1/0
S    192.168.3.0/24 [1/0] via 172.16.34.4
R1#sh mpls for
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop    
tag    tag or VC   or Tunnel Id      switched   interface              
16     17          3.3.3.3/32        0          Fa0/0      172.16.12.2  
17     19          4.4.4.4/32        0          Fa0/0      172.16.12.2  
18     18          172.16.34.0/24    0          Fa0/0      172.16.12.2  
19     Pop tag     172.16.23.0/24    0          Fa0/0      172.16.12.2  
20     Untagged    192.168.3.0/24    0          Fa0/0      172.16.12.2  
21     Pop tag     2.2.2.2/32        0          Fa0/0      172

S 192.168.3.0/24 [1/0] via 172.16.34.4
18 18 172.16.34.0/24 0 Fa0/0 172.16.12.2
20 Untagged 192.168.3.0/24 0 Fa0/0 172.16.12.2

Why is 192.168.3.0/24 untagged ?

Stuart

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