Routing

Expand all | Collapse all

OSPF Sham-link in L3VPN

  • 1.  OSPF Sham-link in L3VPN

    Posted 06-16-2021 09:12

    Hello! I am following JNCIE-SP self study bundle and one of the  task requirements in L3VPN chapter states "Make sure that the customer C1 OSPF area 0 appears as a contiguous area without ABRs." this indirectly hinting inter-area traffic vs intra-area and I understand that. the solution provided by workbook is the sham-link within L3VPN, no issues so far.  here is my confusion, why dont I see any change in ospf db when this change is made?

    self-study workbook shows difference when comparing databases from before and after the change. the difference is the far end lo0.1 IPs not being present in database before establishing sham-links.  when checking my lab I dont see that behavior, I see some differences but I dont think I fully understand them.
    This lab is running on vMX 20.1. I basically want to understand if Im doing something wrong, or if this behavior is expected on junos 20.x? 

    Quick background for those who dont have access to the bundle: there are 4 PE routers handling L3VPN with OSPF as PE-CE. below is a snapshot of one of those routers which shows database before the change, the change I committed and database after the change.

    after this change, the workbook indicates issue is fixed by this statement: "The LSA Type 1 from other PEs are now present in the OSPF database via the sham links. " but we see LSA type 1 prior to this change as well. what am I missing? 


    can someone clarify this for me please? Thanks in advance

    #####DATABASE BEFORE CHANGE#####
    root@R8# run show ospf database instance C1    
    
        OSPF database, Area 0.0.0.0
     Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
    Router   172.30.5.17      172.30.5.17      0x80000024    19  0x22 0xca33  48
    Router   172.30.5.21      172.30.5.21      0x8000001e    21  0x22 0x4fa0  48
    Router   172.30.5.29      172.30.5.29      0x80000020    23  0x22 0x9c21  48
    Router  *172.30.5.37      172.30.5.37      0x80000029    17  0x22 0x7b11  48
    Router   172.31.63.1      172.31.63.1      0x80000038    50  0x22 0xaa62  72
    Router   172.31.63.2      172.31.63.2      0x80000039    49  0x22 0xb91d 120
    Router   172.31.63.3      172.31.63.3      0x8000003e    60  0x22 0xf6a5 120
    Router   172.31.63.4      172.31.63.4      0x8000003d    62  0x22 0x7f6d  72
    Router   172.31.63.5      172.31.63.5      0x80000031  1925  0x22 0xe47c  84
    Network  192.168.0.70     172.31.63.2      0x80000001    49  0x22 0x4f43  32
    Network  192.168.0.74     172.31.63.3      0x80000001    60  0x22 0x6325  32
    Network  192.168.0.86     172.31.63.4      0x80000001    62  0x22 0x5f13  32
    Network  192.168.0.94     172.31.63.1      0x80000001    50  0x22 0x73f4  32
    
    
    ##### ABOUT TO COMMIT THIS CHANGE#####
    ##### .37 is lo0.1 which is part of C1 instance#####
    ##### other IPs are lo0.1 on other PE routers#####
    
    root@R8# show | compare 
    [edit routing-instances C1 protocols ospf area 0.0.0.0]
    +       sham-link-remote 172.30.5.17;
    +       sham-link-remote 172.30.5.21;
    +       sham-link-remote 172.30.5.29;
    [edit routing-instances C1 protocols ospf]
    +      sham-link local 172.30.5.37;
    
    
    #####Current local ospf peer#####
    root@R8# run show ospf neighbor instance C1 
    Address          Interface              State           ID               Pri  Dead
    192.168.0.94     ge-0/0/5.324           Full            172.31.63.1      128    30
    
    [edit]
    root@R8# commit 
    commit complete
    
    [edit]
    root@R8# run show ospf neighbor instance C1 
    Address          Interface              State           ID               Pri  Dead
    192.168.0.94     ge-0/0/5.324           Full            172.31.63.1      128    37
    172.30.5.17      shamlink.0             Full            172.30.5.17        0    31
    172.30.5.21      shamlink.1             Full            172.30.5.21        0    30
    172.30.5.29      shamlink.2             Full            172.30.5.29        0    38
    
    [edit]
    root@R8# run show ospf database instance C1    
    
        OSPF database, Area 0.0.0.0
     Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
    Router   172.30.5.17      172.30.5.17      0x80000028    11  0x22 0x38d3  72
    Router   172.30.5.21      172.30.5.21      0x80000022    14  0x22 0xcf9   72
    Router   172.30.5.29      172.30.5.29      0x80000024    13  0x22 0xf155  72
    Router  *172.30.5.37      172.30.5.37      0x8000002e     7  0x22 0xac78  72
    Router   172.31.63.1      172.31.63.1      0x80000038   253  0x22 0xaa62  72
    Router   172.31.63.2      172.31.63.2      0x80000039   252  0x22 0xb91d 120
    Router   172.31.63.3      172.31.63.3      0x8000003e   263  0x22 0xf6a5 120
    Router   172.31.63.4      172.31.63.4      0x8000003d   265  0x22 0x7f6d  72
    Router   172.31.63.5      172.31.63.5      0x80000031  2128  0x22 0xe47c  84
    Network  192.168.0.70     172.31.63.2      0x80000001   252  0x22 0x4f43  32
    Network  192.168.0.74     172.31.63.3      0x80000001   263  0x22 0x6325  32
    Network  192.168.0.86     172.31.63.4      0x80000001   265  0x22 0x5f13  32
    Network  192.168.0.94     172.31.63.1      0x80000001   253  0x22 0x73f4  32
    
    [edit]
    root@R8# 
    
    #####Copy of the instance for refrence#####
    
    root@R8# show routing-instances C1 
    protocols {
        ospf {
            area 0.0.0.0 {
                sham-link-remote 172.30.5.17;
                sham-link-remote 172.30.5.21;
                sham-link-remote 172.30.5.29;
                interface all;
            }
            sham-link local 172.30.5.37;
        }
    }
    instance-type vrf;
    interface ge-0/0/5.324;
    interface lo0.1;
    vrf-target target:54591:100;


  • 2.  RE: OSPF Sham-link in L3VPN

    Posted 06-18-2021 16:53
    Your post interests me. I started to learn Sham-link on Cisco before.  Right now I am to move to Juniper. So I like to know it too.

    I have not taken a look at yours yet. I am interested in taking a look when I have time.


    thanks !!




  • 3.  RE: OSPF Sham-link in L3VPN

    Posted 06-18-2021 17:16
    I think the  following inside the red is what Type 1 refers to.  Am I right ?

    Hopefully someone else can help to clarify for us.

    thanks !!


  • 4.  RE: OSPF Sham-link in L3VPN

    Posted 06-18-2021 21:02
    Hi Gongyayu,
    Thanks for checking this. Correct! those are know as LSA type 1 or Router LSA's. however the expectation is to see those 3 LSA's (identified by red box in your comment) only after sham-link is turned up in the instance.  this is not the case in my lab. I do see similar LSA's before and after the change. the only diff I notice is the "Len" column changes from 48 to 72 for these 4 LSA's. 

    BEFORE sham-link:
    root@R8# run show ospf database instance C1 
    
        OSPF database, Area 0.0.0.0
     Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
    Router   172.30.5.17      172.30.5.17      0x80000009   732  0x22 0x118   48
    Router   172.30.5.21      172.30.5.21      0x80000009   733  0x22 0x798b  48
    Router   172.30.5.29      172.30.5.29      0x80000008   736  0x22 0xcc09  48
    Router  *172.30.5.37      172.30.5.37      0x80000011   370  0x22 0xabf8  48
    
    
    AFTER shan-link:
    root@R8# run show ospf database instance C1    
    
        OSPF database, Area 0.0.0.0
     Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
    Router   172.30.5.17      172.30.5.17      0x8000000c    28  0x22 0x70b7  72
    Router   172.30.5.21      172.30.5.21      0x8000000d    25  0x22 0x36e4  72
    Router   172.30.5.29      172.30.5.29      0x8000000d    28  0x22 0x203e  72
    Router  *172.30.5.37      172.30.5.37      0x80000016    27  0x22 0xdc60  72
    

    here is an extensive output of the LSA shown above, generated by the same router (R8).
    I see the difference but I dont think I quite understand it.
    root@R8# run show ospf database instance C1 router advertising-router 172.30.5.37 extensive    
    
        OSPF database, Area 0.0.0.0
     Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
    Router  *172.30.5.37      172.30.5.37      0x80000017   200  0x22 0x9ffe  48
      bits 0x1, link count 2
      id 192.168.0.94, data 192.168.0.93, Type Transit (2)
        Topology count: 0, Default metric: 1
      id 172.30.5.37, data 255.255.255.255, Type Stub (3)
        Topology count: 0, Default metric: 0
      Topology default (ID 0)
        Type: Transit, Node ID: 192.168.0.94
          Metric: 1, Bidirectional
      Gen timer 00:46:40
      Aging timer 00:56:40
      Installed 00:03:20 ago, expires in 00:56:40, sent 00:03:20 ago
      Last changed 00:03:20 ago, Change count: 15, Ours
    
    [edit]
    root@R8# commit 
    commit complete
    
    [edit]
    root@R8# run show ospf database instance C1 router advertising-router 172.30.5.37 extensive    
    
        OSPF database, Area 0.0.0.0
     Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
    Router  *172.30.5.37      172.30.5.37      0x8000001c    46  0x22 0xd066  72
      bits 0x1, link count 4
      id 192.168.0.94, data 192.168.0.93, Type Transit (2)
        Topology count: 0, Default metric: 1
      id 172.30.5.17, data 128.1.0.0, Type PointToPoint (1)
        Topology count: 0, Default metric: 1
      id 172.30.5.21, data 128.1.0.1, Type PointToPoint (1)
        Topology count: 0, Default metric: 1
      id 172.30.5.29, data 128.1.0.2, Type PointToPoint (1)
        Topology count: 0, Default metric: 1
      Topology default (ID 0)
        Type: PointToPoint, Node ID: 172.30.5.29
          Metric: 1, Bidirectional
        Type: PointToPoint, Node ID: 172.30.5.21
          Metric: 1, Bidirectional
        Type: PointToPoint, Node ID: 172.30.5.17
          Metric: 1, Bidirectional
        Type: Transit, Node ID: 192.168.0.94
          Metric: 1, Bidirectional
      Gen timer 00:49:14
      Aging timer 00:59:14                  
      Installed 00:00:46 ago, expires in 00:59:14, sent 00:00:46 ago
      Last changed 00:00:46 ago, Change count: 19, Ours​



  • 5.  RE: OSPF Sham-link in L3VPN

    Posted 06-18-2021 21:55
    I got your point.  I need to review it. It is a good  chance for me to review this topic.

    thanks !!


  • 6.  RE: OSPF Sham-link in L3VPN

    Posted 06-19-2021 00:49
    I checked the  material,  you don't expect to see the following:
    Router   172.30.5.29      172.30.5.29      0x80000008   736  0x22 0xcc09  48
    Router  *172.30.5.37      172.30.5.37      0x80000011   370  0x22 0xabf8  48​
    But you saw them before adding sham-link, right ?


  • 7.  RE: OSPF Sham-link in L3VPN

    Posted 06-19-2021 02:07
    I tested more and noticed it might be caused by images. Try to reboot to see whether they change.

    I tested R8 and R6 after reboot
    before adding sham-link
    root@R8# run show ospf database instance CE1 
    
        OSPF database, Area 0.0.0.0
     Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
    Router   172.16.1.1       172.16.1.1       0x80000006   377  0x22 0x5133  72
    Router  *172.30.5.37      172.30.5.37      0x80000004  2202  0x22 0x3eae  48
    
    [edit]​

    After adding sham-link

    root@R8# run show ospf database instance CE1                                                       
    
        OSPF database, Area 0.0.0.0
     Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
    Router   172.16.1.1       172.16.1.1       0x80000006   577  0x22 0x5133  72
    Router   172.16.4.1       172.16.4.1       0x80000005  2359  0x22 0x2762  72
    Router   172.30.5.29      172.30.5.29      0x80000004     9  0x22 0x5121  60
    Router  *172.30.5.37      172.30.5.37      0x80000005     8  0x22 0xb7b5  60
    
    [edit]

    root@R8# run show version
    Hostname: R8
    Model: vmx
    Junos: 14.1R1.10