Routing

 View Only

IMPORTANT MODERATION NOTICE

This community is currently under full moderation, meaning  all posts will be reviewed before appearing in the community. Please expect a brief delay—there is no need to post multiple times. If your post is rejected, you'll receive an email outlining the reason(s). We've implemented full moderation to control spam. Thank you for your patience and participation.



  • 1.  Is there an opposite to generate or aggregate routes?

    Posted 07-05-2022 13:10
    Hi All,

    Scenario: I receive a route - e.g. 10.1.1.0/24 - in the GRT of a router from another router in my network via iBGP. 

    The router in which I receive this route is going to be used to peer with an external AS, and I want to announce a longer mask/more specific route from the 10.1.1.0/24 network to the external peer - e.g. I only want to announce 10.1.1.0/30 to the external peer.

    Is there an 'opposite' of the generate/aggregate route feature - e.g. the contributing route can be shorter (e.g. /24) than the generate/aggregate route (a /30) that I want to announce to the peer?

    P.S. I don't want to configure a static route for the 10.1.1.0/30 subnet in the router I will use to peer with the external AS. 

    In summary: how do I announce the 10.1.1.0/30 to the peer when all I have is a 10.1.1.0/24 in my local GRT (inet.0) without configuring a static route for the 10.1.1.0/30 subnet and redistributing it into eBGP via policy to announce to the external peer?

    TIA


  • 2.  RE: Is there an opposite to generate or aggregate routes?

    Posted 30 days ago
    ***BUMP ***

    Anyone?


  • 3.  RE: Is there an opposite to generate or aggregate routes?

     
    Posted 28 days ago
    I'd suggest to look at condition | Juniper Networks with a semi comprehensible example in the first section of Example: Configuring a Routing Policy for Conditional Advertisement Enabling Conditional Installation of Prefixes in a Routing Table | Juniper Networks ...  Ulf


  • 4.  RE: Is there an opposite to generate or aggregate routes?

     
    Posted 28 days ago
    The problem that this presents for any routing policy creation is that the smaller subnet you want to advertise will need to be active in the local table by some means.

    So the issue is to figure out where the least potentially disruptive place will be to create and then propagate that route. 

    Bearing in mind that since it is a more specific route it will override the larger prefix already being received at this peer having the potential to blackhole or misdirect traffic in some circumstances.

    So in generally, I would think you want to create this more specific subnet as close to the resources within that subnet as possible.  Ideally at the router where those hosts are connected.

    ------------------------------
    Steve Puluka BSEET - Juniper Ambassador
    IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP - Retired)
    http://puluka.com/home
    ------------------------------



  • 5.  RE: Is there an opposite to generate or aggregate routes?

    Posted 28 days ago
    Thanks Spuluka - you've described the problem perfectly - i.e. creating a more specific route and having it active in the local route table of the peering router in order to allow it to be redistributed to the external peer means it overrides the less-specific route which I want the inbound traffic to actually use.

    Creating the more-specific route at the router where those hosts are connected just isn't possible in this particular case.

    I'll have to admit defeat on this one! :(