Trouble with inter and intra area filtering between two areas.

15 Dec 2015

      Hello.

Here's my setup with 4 routers:

   area 0
    /     \
R1 ---- R2
|              |
|              |
R3 ------ R4
 \  area1 /

What I am trying is to prevent routes that fall in 10.0.0.0/8 range from
being announced from Area 1 routers (R3, R4) to Area 0 routers (R1, R2). At
the same time I want Area 1 routers (R3, R4) to exchange these routes
between themselves.

I thought that I could achieve it by using "networks { 10.0.0.0/8 hidden;
};" in Area 1 routers configs. Documentation says: "Hidden networks are not
propagated into other areas." It does indeed prevent annoucement to Area 0
routers from Area 1, but at the same time it also filters these routes out
between Area 1 routers (R3, R4) which is not what I want, I expected it not
getting filtered from Area 1 routers. (Since they are the same area).

Is there any way I can filter 10.0.0.0/8 from reaching Area 0 from Area 1,
but at the same time keep such routes announced between Area 1 routers?

Thank you.

My configs are as follows:

Config for R1:

router id 1.1.1.1;

protocol kernel {
        export all;
}

protocol device {
        scan time 10;
}

protocol static {

}

protocol ospf {
        tick 2;

        area 0.0.0.0 {
                interface "eth0" {
       # interface from R1 to R2
                        dead count 4;
                        type broadcast;
                };
interface "eth1" {
       # interface from R1 to R3
                        dead count 4;
                        type broadcast;
};
        };
}

Config for R2:

router id 2.2.2.2;

protocol kernel {
        export all;
}

protocol device {
        scan time 10;
}

protocol static {

}

protocol ospf {
        tick 2;

        area 0.0.0.0 {
                interface "eth0" {
       # interface from R2 to R1
                        dead count 4;
                        type broadcast;
                };
interface "eth1" {
       # interface from R2 to R4
                        dead count 4;
                        type broadcast;
};
        };
}

Config for R3:

router id 3.3.3.3;

protocol kernel {
        export all;
}

protocol device {
        scan time 10;
}

protocol static {

}

protocol ospf {
        tick 2;

        area 0.0.0.0 {
                interface "eth0" {
# interface from R3 to R1
                        dead count 4;
                        type broadcast;
                };
        };

        area 0.0.0.1 {
                stub yes;
                summary no;

                networks {
                        10.0.0.0/8 hidden;
                };

                interface "eth1" {
# interface from R3 to R4
                        cost 1000;
                        dead count 4;
                        type broadcast;
                };

                interface "ppp*" {
                        stub yes;
                };
        };
}

Config for R4:

router id 4.4.4.4;

protocol kernel {
        export all;
}

protocol device {
        scan time 10;
}

protocol static {

}

protocol ospf {
        tick 2;

        area 0.0.0.0 {
                interface "eth0" {
# interface from R4 to R2
                        dead count 4;
                        type broadcast;
                };
        };

        area 0.0.0.1 {
                stub yes;
                summary no;

                networks {
                        10.0.0.0/8 hidden;
                };

                interface "eth1" {
# interface from R4 to R4
                        cost 1000;
                        dead count 4;
                        type broadcast;
                };

                interface "ppp*" {
                        stub yes;
                };
        };
}

LU

Ondrej Zajicek

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