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Can I make JUNOS advertise two /26's in BGP from a single /25 route in the RIB?

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  • 1.  Can I make JUNOS advertise two /26's in BGP from a single /25 route in the RIB?

    Posted 05-08-2018 07:27

    Scenario.  I am assigned a /25 lan block from the ISP.  They allow us to carve that up into two /26's so we can load share across two circuits.  (Think advertise /26 A out Circuit A and /26 B + prepended out Circuit A, and vice versa for Circuit B)

     

    My problem is this.  On the inside/LAN side interface I have the entire /25 lan block configured on the interface.

     

    My device (SRX) does not want to advertise the two /26's.  I'm thinking the exact /26 must be in my routing table for the advertisement to work.  So at this point I'm wondering if there is any work around.

     

    Here's the partial config.  I am thinking it doesn't work because I lack the exact /26 routes in my table.  Is there a way to get around this.  I'd like to advoid configuring them separately unless there is no work around.

     

    interfaces {
        ge-0/0/0 {
            description "LAN INTERFACE";
            }
            unit 0 {
                family inet {
                    address 10.10.10.0/25;
    
    policy-options {
        prefix-list SUBNET-A {
            10.10.10.0/26;
        }
        prefix-list SUBNET-B {
            10.10.10.64/26;
        policy-statement CIRCUIT-A-OUT {
            term SUBNET-A-TERM {
                from {
                    prefix-list SUBNET-A;
                }
                then accept;
            }
            term SUBNET-B-TERM {
                from {
                    prefix-list SUBNET-B;
                }
                then {
                    as-path-prepend "65001 65001";
                    accept;
    protocols {
                bgp {
                    group ISP-GROUP {
                        type external;
                        peer-as 65002;
                        neighbor 1.1.1.1 {
                            import DEFAULT-IN;
                            export CIRCUIT-A-OUT;
    
    
    


  • 2.  RE: Can I make JUNOS advertise two /26's in BGP from a single /25 route in the RIB?
    Best Answer

    Posted 05-08-2018 09:13

    Hello,

    Of course there is a way.  

    "BGP-static" routes would be the perfect candidate feature ( https://www.juniper.net/documentation/en_US/junos/topics/example/example-configuring-bgp-static-routes.html ) but since it is not supported on SRX (MX only), You can configure two /26 statics to point to the network IP of covering /25:

     

    set routing-options static route 10.10.10.0/26 next-hop 10.10.10.0 no-install
    set routing-options static route 10.10.10.64/26 next-hop 10.10.10.0 no-install

    This way, the two /26 will be:

    1/ present in the RIB but not in the FIB (at least how it behaves in my virtual lab)

    2/ removed from RIB if ge-0/0/0 goes down.

    And You can advertise these two /26 via eBGP out, as You normally do with any other static route.

    HTH

    Thx
    Alex



  • 3.  RE: Can I make JUNOS advertise two /26's in BGP from a single /25 route in the RIB?

    Posted 05-08-2018 10:21

    The perfect solution accomplishing exaclty what I was hoping to achieve.  Thanks much!