Thank you very much to all for your replies, public or private. I should have said that we do not use LACP. Remote firewall admins confirmed that there is no LACP, there wasn't LACP on the previous MX5 and when I put the 10G switch in beetween, there is no LACP configured (I should check if there is not LACP behind the curtain by default).
So this is plain 802.3ad LAG, without LACP. Multiple answers said that LAG is not supported at 1G and here is a link [1] (thanks Adrien Desportes) that says: On MX10003 and MX204 routers, Link Aggregation Group (LAG) is supported on 10-Gbps speed only. It is not supported on 1-Gbps speed. [1] https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/speed-gigether-options.html I wasn't aware of this limitation. So I'm puzzled by Alexandre Snarskii's reply who shows a working 1G LACP LAG on 18.4R3-S6.3. I'm running 19.4R1.10. I'll try a LAG with my switch first to be sure of it. Thanks again to everybody, -- Emmanuel Halbwachs DIO/CASTORS/Resp. Réseau,Sécurité Observatoire de Paris ✆ +33 1 45 07 75 54 Campus Paris : 61 av. de l'Observatoire F 75014 PARIS Campus Meudon : 11 av. Marcellin Berthelot F 92190 MEUDON _______________________________________________ juniper-nsp mailing list juniper-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/juniper-nsp