Routing

i like to create a policy for the conditional advertisement of default route to a bgp customer i.e. the default routes (0.0.0.0/0) only advertised if another route (say 1.1.0.0/16) presents. Following are two ways which comes into my mind and appreciate if  one can provide your feedback if the following can fullfill the requirement. If both can work than which one could be the recommended one.

Thanks

-------------------------------

---- OPTION 1 -----------------

-------------------------------

[edit routing-options]

aggregate {

    route 1.1.0.0/16;

}

generate {

    route 0.0.0.0/0 discard;

}

[edit policy-options]

policy-statement bgpcust-default-out {

    term 10 {

        from {

            route-filter 0.0.0.0/0 exact;

            route-filter 1.1.0.0/16 exact;

        }

        then {

            community delete all;

            accept;

        }

    }

}

community all members *:*;

[edit protocols bgp]

group External {

    neighbor 99.99.99.1 {

        export bgpcust-default-out;

        peer-as 65100;

    }

}

-------------------------------

---- OPTION 2 -----------------

-------------------------------

[edit routing-options]

generate {

    route 0.0.0.0/0 {

        policy if-default-network-exists;

        discard;

    }

}

[edit policy-options]

policy-statement if-default-network-exists {

    term DEFAULT_ROUTE {

        from {

            route-filter 1.1.0.0/16 exact;

        }

        then accept;

    }

    term reject-all-other-routes {

        then reject;

    }

}

policy-statement bgpcust-defaultroute-out {

    term 1 {

        from {

            route-filter 0.0.0.0/0 exact;

        }

        then {

            community delete all;

            accept;

        }          

    }

}

community all members *:*;

[edit protocols bgp]

group External {

    neighbor 100.100.100.1 {

        export bgpcust-defaultroute-out;

        peer-as 65100;

    }

}

Hi MSC,

OPTION 2 will work for you and, it is the perfect way for conditional route advertisement..

OPTION 1 will not work for you.

Regards

Satinder Singh

Hello Satinder,

I tried to test it but the default route is not coming up in the routing table so it is not advertised to the peer. The other route 1.1.0.0/16 is in the routing table but it is also have discard so not sure if that making a difference.

HI MSC,

Can you remove discard and see if it make any difference, I don't think it is a problem.

Also please send the output of "sh route  1.1.0.0/16 detail"

Regards

Satinder

The matching route  (1.1.0.0/16) is generated from the route-reflector.  I tried to generate it locally using the aggregate command without discard but that didn't resolve the issue.

1.1.0.0/16     *[BGP/170] 00:51:03, localpref 100, from x.x.x.11
                      AS path: I, validation-state: unverified
                      Discard
                    [BGP/170] 00:50:25, localpref 100, from x.x.x.22
                      AS path: I, validation-state: unverified
                      Discard

Hi,

It looks issue with 1.1.0.0/16 route.

Could you create a static route (1.1.0.0/16 ) with valid next hop (instead of discard). Hope this will activate 0/0 ?

Regards

Satinder Singh

It is kind of a supernet so there is no such valid next-hop and don't want to have traffic forwarded to 1.1.0.0/16 so that's why configuring it as discard.

One thing I don't get. If you are receiving the route from the RR, why do you have this?

[edit routing-options]

aggregate {

    route 1.1.0.0/16;

}

How does the route look like when you remove that bit of config?

Hello Satinder,

I test the option 2 which DOESN'T have  the following statement. This statement is in option 1.

aggregate {

    route 1.1.0.0/16;

}

Can you send the output of:

show route receive-protocol bgp 1.1.0.0/16 x.x.x.11

Whatever x is. Thanks,

Ato

Hello Ato,

Here is the output. x.x.x.35 is the route reflector which has 1.1.0.0/16 defined as static route with discard.

router#run show route receive-protocol bgp 1.1.0.0/16  x.x.x.35           

inet.0: 375481 destinations, 375624 routes (375479 active, 0 holddown, 2 hidden)
Restart Complete

inet.3: 72 destinations, 72 routes (72 active, 0 holddown, 0 hidden)
Restart Complete

export policy if-default-network-exists should be exported in bgp protocol. Give the export if-default-network-exists in the edit protocols bgp and check.

I am exporting "bgpcust-defaultroute-out". Why "if-default-network-exists" needed to be exported ?

It is only to check and conditionally geenrate default route.

one modification

policy-statement bgpcust-defaultroute-out {
term 1 {
from {
protocol aggregate;
route-filter 0.0.0.0/0 exact;
}
then {
community delete all;
accept;
}
}
}
community all members *:*;

The route is generated by using the generate command. Thanks lyndidon and other for the feebback. I make it working by tweaking the policy little bit.

policy-statement if-default-network-exists {
    term DEFAULT_ROUTE {
        from {
            route-filter 1.1.0.0/16 exact;
        }
        then accept;
    }
}

policy-statement bgpcust-default-out {
    term 10 {
        from {
            route-filter 1.1.0.0/16 exact;
        }
        then {
            community delete all-communities;
            accept;
        }
    }
    term 20 {
        then reject;
    }
}

If the route is generated by bgp then you also need to modify statement like this:

[edit policy-options]

policy-statement if-default-network-exists {

    term DEFAULT_ROUTE {

        from {

            protocol bgp;

            route-filter 1.1.0.0/16 exact;

        }

        then accept;

    }

    term reject-all-other-routes {

        then reject;