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.
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Steve Puluka BSEET - Juniper Ambassador
IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP - Retired)
http://puluka.com/home------------------------------
Original Message:
Sent: 07-05-2022 13:10
From: Unknown User
Subject: Is there an opposite to generate or aggregate routes?
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