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You are here: Home / Juniper / OSPF ABR will not generate default LSA to stub area when area 0 has only one router

OSPF ABR will not generate default LSA to stub area when area 0 has only one router

June 27, 2016 by Marques Brownlee

How to inject a default route to address the OSPF area border router (ABR) not generating a default link-state advertisement (LSA) to stub area when area 0 has only one router.

When area 0 has only one router, OSPF ABR will not generate default LSA to stub area. We need to inject default route to stub area.

Topology:

SRX240A(ge-0/0/2)---|---(ge-0/0/2)SRX240B
                    |
        area0       |       area1(stub)

Configuration:
SRX240A:
interfaces {
    ge-0/0/2 {
        unit 0 {
            family inet {
                address 10.10.10.1/30;
            }
        }
    }
    lo0 {
        unit 0 {
            family inet {
                address 10.1.1.1/32;
            }
        }
    }
}
protocols {
    ospf {
        area 0.0.0.1 {
            stub default-metric 10;
            interface ge-0/0/2.0;
        }
        area 0.0.0.0 {
            interface lo0.0;
        }
    }
}

SRX240B:
interfaces {
    ge-0/0/2 {
        unit 0 {
            family inet {
                address 10.10.10.2/30;
            }
        }
    }
    lo0 {
        unit 0 {
            family inet {
                address 10.2.2.2/32;
            }
        }
    }
}
protocols {
    ospf {
        area 0.0.0.1 {
            stub;
            interface ge-0/0/2.0;
        }
    }
    stp;
}

[email protected]# run show ospf database 
    OSPF database, Area 0.0.0.0
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
Router  *10.1.1.1         10.1.1.1         0x80000002  2059  0x22 0x38d1  36
Summary *10.10.10.0       10.1.1.1         0x80000004  1418  0x22 0xa26e  28

    OSPF database, Area 0.0.0.1
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
Router  *10.1.1.1         10.1.1.1         0x80000003  1418  0x20 0x7266  36
Router   10.2.2.2         10.2.2.2         0x800001b3  1419  0x20 0xe23e  36
Network  10.10.10.2       10.2.2.2         0x80000001  1419  0x20 0xbb36  32
Summary *10.1.1.1         10.1.1.1         0x80000002   343  0x20 0x9291  28


[email protected]# run show ospf database 

    OSPF database, Area 0.0.0.1
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
Router   10.1.1.1         10.1.1.1         0x80000003  1437  0x20 0x7266  36
Router  *10.2.2.2         10.2.2.2         0x800001b3  1436  0x20 0xe23e  36
Network *10.10.10.2       10.2.2.2         0x80000001  1436  0x20 0xbb36  32
Summary  10.1.1.1         10.1.1.1         0x80000002   362  0x20 0x9291  28

[edit]
[email protected]# run show route protocol ospf         

inet.0: 7 destinations, 7 routes (7 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.1.1.1/32        *[OSPF/10] 00:24:04, metric 1
                    > to 10.10.10.1 via ge-0/0/2.0
224.0.0.5/32       *[OSPF/10] 2w0d 18:01:23, metric 1
                      MultiRecv

Junos OS supports active backbone detection. Active backbone detection is implemented to verify that ABRs are connected to the backbone. If the connection to the backbone area is lost, then the routing device’s default metric is not advertised, effectively rerouting traffic through another ABR with a valid connection to the backbone.

Junos OS does not generate the default LSA if ABR does not have any active backbone connection (any adjacency in area 0). If only one router exist in area 0, there is a hidden command which will change this behavior. You can configure following command on ABR.

[email protected]#set protocols ospf no-active-backbone  ####Hidden Command ####
[edit]
[email protected]# run show ospf database 

    OSPF database, Area 0.0.0.0
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
Router  *10.1.1.1         10.1.1.1         0x80000002  2133  0x22 0x38d1  36
Summary *10.10.10.0       10.1.1.1         0x80000004  1492  0x22 0xa26e  28

    OSPF database, Area 0.0.0.1
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
Router  *10.1.1.1         10.1.1.1         0x80000003  1492  0x20 0x7266  36
Router   10.2.2.2         10.2.2.2         0x800001b3  1493  0x20 0xe23e  36
Network  10.10.10.2       10.2.2.2         0x80000001  1493  0x20 0xbb36  32
Summary *0.0.0.0          10.1.1.1         0x80000001     9  0x20 0x9c8b  28   <---HERE
Summary *10.1.1.1         10.1.1.1         0x80000002   417  0x20 0x9291  28


[email protected]# run show ospf database 

    OSPF database, Area 0.0.0.1
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len 
Router   10.1.1.1         10.1.1.1         0x80000003  1516  0x20 0x7266  36
Router  *10.2.2.2         10.2.2.2         0x800001b3  1515  0x20 0xe23e  36
Network *10.10.10.2       10.2.2.2         0x80000001  1515  0x20 0xbb36  32
Summary  0.0.0.0          10.1.1.1         0x80000001    34  0x20 0x9c8b  28   <---HERE
Summary  10.1.1.1         10.1.1.1         0x80000002   441  0x20 0x9291  28

[edit]
[email protected]# run show route protocol ospf 

inet.0: 8 destinations, 8 routes (8 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

0.0.0.0/0          *[OSPF/10] 00:00:38, metric 11        <---HERE
                    > to 10.10.10.1 via ge-0/0/2.0
10.1.1.1/32        *[OSPF/10] 00:25:20, metric 1
                    > to 10.10.10.1 via ge-0/0/2.0
224.0.0.5/32       *[OSPF/10] 2w0d 18:02:39, metric 1
                      MultiRecv

 

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Filed Under: Juniper Tagged With: ABR, area border router

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