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  • 1.  LDP MPLS Policy export not working as expected

    Posted 02-21-2024 22:37

    Hi, 

    I'm currenly studdying for the JNCIS-SP exam.  I'm using Juniper V-LAB to test my knowledge.  For this lab I used the topology named "Intra-AS BGP-CT" which is preety simple 5 VMX router connected in one line to each others.

    I have attached to this post my own topology and router configuration. I start each lab session by erasing the current router configuration and paste mine to do my lab session.

    I have configured on PE1 a policy export to reinsert the network 192.168.200.0/30 in the MPLS topology. But it doesn't seem to work as I expect.  Using "show route 192.168.200.0/30 advertising-protocol bgp 192.168.2.4 " is currently provide no output.  On PE2 I don't get any route for 192.168.200.0/30 as I expect.

    I also include the traceoption output for flag "route, address & policy" been set.

    Thank you



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    Attachment(s)

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    p.txt   2 KB 1 version
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    pe1.txt   3 KB 1 version
    txt
    ce1.txt   2 KB 1 version
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    DEBUG_LDP.txt   6 KB 1 version
    txt
    ce2.txt   2 KB 1 version
    txt
    pe2.txt   3 KB 1 version
    pdf
    Intra-AS BGP-CT.pdf   53 KB 1 version


  • 2.  RE: LDP MPLS Policy export not working as expected

    Posted 02-22-2024 08:51

    Hi, 

    1. You do not advertise in BGP that prefix, that's why you do not see it, 192.168.200.0/30 is the subnet between CE-PE, usually you will insert this in your IGP as passive if for whatever reason you don't use BGP NHS.
    2. An Egress LDP policy should be written with care, you should specifically allow your Lo0 and your new FEC in the policy statements. 

    What I will do in your LAB to test egress policy, I will insert the link as passive in IGP, advertise BGP CE routes without NHS, and on remote-PE (PE2) you should see that 10.1.x.x networks have a NH of 192.168.200.2 which is resolved by LDP in inet.3 table because of the egress policy. 

    You need to make sure that 192.168.200.2 is in the inet0 table because of how LDP works, LDP always checks IGP before accepting a label binding. 



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    Bandiu Alin-Filip-Gabriel
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  • 3.  RE: LDP MPLS Policy export not working as expected

    Posted 02-22-2024 08:52

    Hi, 

    You're not seeing the BGP route because you do not advertise it to your peer.  

    set protocols bgp group ISP export pol-CUST
    set policy-options prefix-list pre-CUST 10.1.0.0/24 set policy-options prefix-list pre-CUST 10.1.1.0/24 set policy-options prefix-list pre-CUST 10.1.2.0/24 set policy-options prefix-list pre-CUST 10.1.3.0/24

    Your prefix list referenced in the policy does not match 192.168.200.0/30. 

    For LDP Egress policy you need to make sure that you include in your policy the prefix you want to advertise and also the Lo0 address. This policy needs to accept all the FECs you want to share. 

    Also for this to work you need to have the 192.168.200.0/30 in your IGP as passive because you're not doing BGP NHS and because how LDP works. 



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    Bandiu Alin-Filip-Gabriel
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