I tested my dns servers with the oarc test and my size limit is at least 1403 bytes. I performed the same test before my Juniper ISG 2000 and the result is 2047 bytes. According to the chapter IP "Fragments Filtered" and this article, I think I have a fragmentation problem. This article talks about ip virtual-reassembly for cisco but I can't find the equivalent for Juniper. I prefer to find the good option in JunOS before I talk about this with my net admin :-) Thanks