About Up/Down bit of ISIS in MPLS VPN

hi guys:

MPLS and VPN Architecture Volume?:

"the Up/Down bit is set when redistributing a route from a higer level to a lower level(such as form the MPLS VPN backbone into Level 2 or Level 1)"


but how to check whether the Up/Down bit has already been set up?

Comments

  • You can check the down-bit from the lower level protocol, e.g. OSPF, database. The "Down" (If I recall correctly by heart) will appear in the OSPF DB if the particular prefix has been brought into the process from a MPLS/VPN super backbone.

  • Hi qasdrp,

    I don't know exactly DN bit also there in ISIS (if ISIS has some sort of same caveats of OSPF). Yes there is attach bit by L1/L2 router also can say ABR, which inject the default route to L1 router with attached bit. But for sure this OSPF example helps you to understand DN bit, domian-ID and domain TAG.

    The DN bit is the mechanism to prevent the inter-area loop. When you
    have a inter-area route with DNbit, router doesn't install into the
    routing table. If you verify on OSPF database, you can see the route but
    doesn't install into the routing table.

    R2#show ip route vrf B
    <removed>
    Gateway of last resort is not set

          23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    C        23.23.23.0/24 is directly connected, FastEthernet1/1
    L        23.23.23.2/32 is directly connected, FastEthernet1/1
          192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks
    C        192.168.3.0/24 is directly connected, FastEthernet2/0.2
    L        192.168.3.2/32 is directly connected, FastEthernet2/0.2
    !

    R2#show ip ospf database

                OSPF Router with ID (192.168.3.2) (Process ID 123)

                    Router Link States (Area 0)

    Link ID         ADV Router      Age         Seq#       Checksum Link count
    192.168.3.2     192.168.3.2     730         0x80000002 0x001A5B 1
    192.168.3.4     192.168.3.4     731         0x8000000C 0x00085B 1

                    Net Link States (Area 0)

    Link ID         ADV Router      Age         Seq#       Checksum
    192.168.3.4     192.168.3.4     731         0x80000001 0x00ACCD

                    Summary Net Link States (Area 0)

    Link ID         ADV Router      Age         Seq#       Checksum
    8.8.8.8         192.168.3.4     490         0x80000001 0x006BBE
    23.23.23.0      192.168.3.2     766         0x80000001 0x002761
    58.58.58.0      192.168.3.4     490         0x80000001 0x00A2F9
    88.88.88.88     192.168.3.4     490         0x80000001 0x00FCEB
    !

    R2#show ip ospf database summary 8.8.8.8

                OSPF Router with ID (192.168.3.2) (Process ID 123)

                    Summary Net Link States (Area 0)

      LS age: 518
      Options: (No TOS-capability, DC, Downward)
      LS Type: Summary Links(Network)
      Link State ID: 8.8.8.8 (summary Network Number)
      Advertising Router: 192.168.3.4
      LS Seq Number: 80000001
      Checksum: 0x6BBE
      Length: 28
      Network Mask: /32
            MTID: 0         Metric: 2

    There are three different methods to ignore DN BIT.

    1. Using capability vrf-lite

    R2#show run | section router ospf
    router ospf 123 vrf B
     log-adjacency-changes
     capability vrf-lite
     network 23.23.23.2 0.0.0.0 area 1
     network 192.168.3.0 0.0.0.255 area 0
    R2#show ip route vrf B ospf
    <removed>
    Gateway of last resort is not set

          8.0.0.0/32 is subnetted, 1 subnets
    O IA     8.8.8.8 [110/3] via 192.168.3.4, 00:00:27, FastEthernet2/0.2
          58.0.0.0/24 is subnetted, 1 subnets
    O IA     58.58.58.0 [110/2] via 192.168.3.4, 00:00:27, FastEthernet2/0.2
          88.0.0.0/32 is subnetted, 1 subnets
    O IA     88.88.88.88 [110/3] via 192.168.3.4, 00:00:27, FastEthernet2/0.2

    2. If the domain-id is same, OSPF treates the routes are coming from Inter-area:

    R4#show ip bgp vpnv4 rd 100:2 8.8.8.8
    BGP routing table entry for 100:2:8.8.8.8/32, version 29
    Paths: (1 available, best #1, table B)
      Not advertised to any peer
      Local
        5.5.5.5 (metric 2) from 5.5.5.5 (5.5.5.5)
          Origin incomplete, metric 2, localpref 100, valid, internal, best
          Extended Community: RT:100:2 OSPF DOMAIN ID:0x0005:0x000000170200
            OSPF RT:0.0.0.0:2:0 OSPF ROUTER ID:58.58.58.5:0
          mpls labels in/out nolabel/23
    If domain-id is same, it doesn't install the route into routing table, so, you can change the domain-id.

    R2#show run | section router ospf
    router ospf 123 vrf B
     log-adjacency-changes
     network 23.23.23.2 0.0.0.0 area 1
     network 192.168.3.0 0.0.0.255 area 0
    !

    R2#show ip route vrf B

    <removed>
    Gateway of last resort is not set

          23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    C        23.23.23.0/24 is directly connected, FastEthernet1/1
    L        23.23.23.2/32 is directly connected, FastEthernet1/1
          192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks
    C        192.168.3.0/24 is directly connected, FastEthernet2/0.2
    L        192.168.3.2/32 is directly connected, FastEthernet2/0.2

    Now I changed domain-id value on PE router:

    R4(config-router)#router ospf 23 vrf B
    R4(config-router)#domain-id type 0005 value 000000170100

    Remember if you have different domain-id,  OSPF treates as a external routes.

    R2#show ip route vrf B
    <removed>
    Gateway of last resort is not set

          8.0.0.0/32 is subnetted, 1 subnets
    O E2     8.8.8.8 [110/2] via 192.168.3.4, 00:00:22, FastEthernet2/0.2
          23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    C        23.23.23.0/24 is directly connected, FastEthernet1/1
    L        23.23.23.2/32 is directly connected, FastEthernet1/1
          58.0.0.0/24 is subnetted, 1 subnets
    O E2     58.58.58.0 [110/1] via 192.168.3.4, 00:00:22, FastEthernet2/0.2
          88.0.0.0/32 is subnetted, 1 subnets
    O E2     88.88.88.88 [110/2] via 192.168.3.4, 00:00:22, FastEthernet2/0.2
          192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks
    C        192.168.3.0/24 is directly connected, FastEthernet2/0.2
    L        192.168.3.2/32 is directly connected, FastEthernet2/0.2

    3. The basic formation of OSPF Domain-ID is based on OSPF process ID,
    if you use the different OSPF process id on different sites,  there
    will be different OSPF domain-Id and OSPF treates as a external routes
    rather than inter-area routes.

    R4(config-router)#router ospf 23 vrf B
    R4(config-router)#domain-id type 0005 value 000000170100
    R4(config-router)#no domain-id type 0005 value 000000170100
    !

    R2#show ip route vrf B
    <removed>
    Gateway of last resort is not set

          23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    C        23.23.23.0/24 is directly connected, FastEthernet1/1
    L        23.23.23.2/32 is directly connected, FastEthernet1/1
          192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks
    C        192.168.3.0/24 is directly connected, FastEthernet2/0.2
    L        192.168.3.2/32 is directly connected, FastEthernet2/0.2

    Now I changed the OSPF process id in another router,

    R5#show running-config | section router ospf
    router ospf 231 vrf B
     log-adjacency-changes
     redistribute bgp 100 subnets
     network 58.58.58.5 0.0.0.0 area 0
    !

    R4#show ip bgp vpnv4 rd 100:2 8.8.8.8
    BGP routing table entry for 100:2:8.8.8.8/32, version 46
    Paths: (1 available, best #1, table B)
      Not advertised to any peer
      Local
        5.5.5.5 (metric 2) from 5.5.5.5 (5.5.5.5)
          Origin incomplete, metric 2, localpref 100, valid, internal, best
          Extended Community: RT:100:2 OSPF DOMAIN ID:0x0005:0x000000E70200
            OSPF RT:0.0.0.0:2:0 OSPF ROUTER ID:58.58.58.5:0
          mpls labels in/out nolabel/20
    !

    R2#show ip route vrf B
    <removed>

    Gateway of last resort is not set

          8.0.0.0/32 is subnetted, 1 subnets
    O E2     8.8.8.8 [110/2] via 192.168.3.4, 00:02:02, FastEthernet2/0.2
          23.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    C        23.23.23.0/24 is directly connected, FastEthernet1/1
    L        23.23.23.2/32 is directly connected, FastEthernet1/1
          58.0.0.0/24 is subnetted, 1 subnets
    O E2     58.58.58.0 [110/1] via 192.168.3.4, 00:02:02, FastEthernet2/0.2
          88.0.0.0/32 is subnetted, 1 subnets
    O E2     88.88.88.88 [110/2] via 192.168.3.4, 00:02:02, FastEthernet2/0.2
          192.168.3.0/24 is variably subnetted, 2 subnets, 2 masks
    C        192.168.3.0/24 is directly connected, FastEthernet2/0.2
    L        192.168.3.2/32 is directly connected, FastEthernet2/0.2

    HAPPY STUDY

    [:D]

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