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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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    Xine
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    Attachment(s)

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


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

    Posted 02-22-2024 04:09

    Hi there, 

    LDP is mpls signalling protocol for interchange of mpls labels not ip networks. 
    I advise you to open documentation and start to do basic labs as shown there with configuration. 

    https://www.juniper.net/documentation/us/en/software/junos/mpls/topics/topic-map/ldp-overview.html

    The documentation goes from basics to more complex network cases. 
    For JNCIS you don't have to dive deep into all nuances, but review all main topics in "MPLS Fundamentals" course in basic. 
    You can also download documentation as PDF (in the right corner of the web page) and open LDP overview chapter. 
    Note that the Documentation file like advanced Student Guide concerned to a topic. 
    So for every topic Juniper has now documentation in one pdf file. 



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    WBW,
    Dmitriy
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  • 3.  RE: LDP MPLS Policy export not working as expected

    Posted 02-22-2024 22:44

    Hi Dmitriy, 

    I send a new post replying to my inital of last evening, if you can take a look.

    Thank you



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

    Posted 02-22-2024 04:42

    Well, the answer is simple enough - your export policy "pol-CUST" for "ISP" BGP group does not match 192.168.200.0/30. Adding this prefix to "pre-CUST" prefix-list should solve the problem.

    I assume that you're doing this to fix next-hop problem of prefixes, received from eBGP (CE1) and advertised to iBGP (PE2). In that the best solution would be to use next-hop-self in the export policy to PE2. Other way would be to enable IS-IS on that interface, but keep it passive.

    Hopefully this solves your problem.



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    FARID AKHUNDOV
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  • 5.  RE: LDP MPLS Policy export not working as expected

    Posted 02-22-2024 22:45

    Hi Farid,

    I send a new post replying to my inital of last evening, if you can take a look.

    Thank you



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

    Posted 02-22-2024 22:42

    Hi, 

    I discussed with a colleague this afternoon and we have finally find a way to make it work.

    BGP session between PE1 and PE2 has been disabled.

    The following configuration been applied on PE1

    set policy-options policy-statement EGRESS_LDP term EXPORT from protocol direct
    set policy-options policy-statement EGRESS_LDP term EXPORT then accept

    set protocols ldp egress-policy EGRESS_LDP

    The interface GE-0/0/0 is advertised in the IGP (my case ISIS) as passive interface

    on PE2 I did similar but instead list individual interface I decide to use sentence "from protocol direct"

    again the interface ge-0/0/1 is advertized in the IGP as passive interface (since no neighbor is present)

    This makes prefix 192.168.200.0/30 be advertised with label to PE2 by PE1, and prefixe 192.168.3.0/30 is now advertized to PE1 with label by PE2.  To see the difference the BGP session between router has to be disabled.

    This makes 192.168.200.1 be reachable from PE2 using labels.  But it not enough to make network present on CE1 be reachable.  The reverse is also true 192.168.3.1 is reachable from PE1 using label but network on CE2 aren't.

    Now what would be interesting use case for this ?  

    The route with label is present in routing table 

    jcluser@PE1# run show route 192.168.3.0/30 extensive                                    
     
    inet.0: 20 destinations, 20 routes (20 active, 0 holddown, 0 hidden)
    192.168.3.0/30 (1 entry, 1 announced)
            State: <FlashAll>
    TSI:
    KRT in-kernel 192.168.3.0/30 -> {192.168.211.1}
            *IS-IS  Preference: 18
                    Level: 2
                    Next hop type: Router, Next hop index: 615
                    Address: 0xc4b8c84
                    Next-hop reference count: 8
                    Next hop: 192.168.211.1 via ge-0/0/1.0, selected
                    Session Id: 0x141
                    State: <Active Int>
                    Local AS: 65500 
                    Age: 21:36 Metric: 30 
                    Validation State: unverified 
                    ORR Generation-ID: 0 
                    Task: IS-IS
                    Announcement bits (2): 0-KRT 6-LDP 
                    AS path: I 
                    Thread: junos-main 
     
    inet.3: 3 destinations, 3 routes (3 active, 0 holddown, 0 hidden)
     
    192.168.3.0/30 (1 entry, 1 announced)
            State: <FlashAll>
            *LDP    Preference: 9
                    Next hop type: Router, Next hop index: 0
                    Address: 0xc4b8e8c
                    Next-hop reference count: 2
                    Next hop: 192.168.211.1 via ge-0/0/1.0, selected
                    Label operation: Push 299904
                    Label TTL action: prop-ttl
                    Load balance label: Label 299904: None; 
                    Label element ptr: 0xcbc5b10
                    Label parent element ptr: 0x0
                    Label element references: 1
                    Label element child references: 0
                    Label element lsp id: 0
                    Session Id: 0x0
                    State: <Active Int>
                    Local AS: 65500 
                    Age: 21:36 Metric: 1 
                    Validation State: unverified 
                    Task: LDP
                    Announcement bits (1): 4-Resolve tree 5 
                    AS path: I              
                    Thread: junos-main 

    but the route with the label doesn't looks to be installed in the forwarding table :

      

    jcluser@PE1# run show route forwarding-table matching 192.168.3.0/30 extensive 
    Routing table: default.inet [Index 0] 
    Internet:
        
    Destination:  192.168.3.0/30
      Route type: user                  
      Route reference: 0                   Route interface-index: 0   
      Multicast RPF nh index: 0             
      P2mpidx: 0              
      Flags: sent to PFE, rt nh decoupled  
      Nexthop: 192.168.211.1
      Next-hop type: unicast               Index: 615      Reference: 11   
      Next-hop interface: ge-0/0/1.0   
     
    Routing table: __pfe_private__.inet [Index 3] 
    Internet:
     
    Routing table: __juniper_services__.inet [Index 5] 
    Internet:
     
    Routing table: __master.anon__.inet [Index 6] 
    Internet:

    I undersatand that it can be useful when 2 router can't have BGP session be established for some reason, but if I have to set static route to make network be reachable over this MPLS session I'm questionning the benefit at the end.  May for Carier over Carier topology ?

    attached to this new post the 2 new routers configurations.

    Thank you



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    Xine
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    Attachment(s)

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    pe2.txt   3 KB 1 version
    txt
    pe1.txt   3 KB 1 version