From Emmanuel.Halbwachs at obspm.fr  Fri Apr 17 10:49:49 2026
From: Emmanuel.Halbwachs at obspm.fr (Emmanuel Halbwachs)
Date: Fri, 17 Apr 2026 16:49:49 +0200
Subject: [j-nsp] Doing SNAT only for destinations learned from a specific BGP
 peering
Message-ID: <aeJIjSNpdBGjDlM_@bop.lan>

Hello,

On MX204 or MX80, is there a way to configure source NAT only for
destinations learned from a BGP peering?

Details:

We are a public research institution. For some reason, we need to
connect to a government network N that is only reachable throught a
L3VPN. So we have a BGP peering with a /31 prefix (say x.x.x.0 the
peer and x.x.x.1 us). All servers in this particular network are
filtered and only accessible if source address is x.x.x.1 (our side of
the peering).

So I have do to source NAT for all our hosts that want to reach
servers in N. I have ≈ 800 routes learned through the peering.

I've never done NAT in the Junos world, only basic routing and basic
BGP.

What are the best way to do this NAT on MX routers only for the
destinations learned from a specific BGP peering?

Any help or clue will be much appreciated!

Thanks and have a nice week-end,

-- 
Emmanuel Halbwachs, Observatoire de Paris, ✆ +33 1 45 07 75 54
DIO¹ / CASTORS² 🦫 / PANDA³ 🐼
¹ Direction Informatique de l'Observatoire ; ² CAlcul, STOckage, Réseau, Système
³ Pool of Awesome Network Devices Administrators