We ran into a strange situation yesterday that I am still trying to figure out. We have many VoIP customers but yesterday suddenly select few of them couldn't reach the SIP provider's network from our network. I could traceroute to the SIP providers server from the affected clients' IP just fine. I confirmed that the SIP traffic was leaving our network out the interface to the upstream provider and the SIP provider says they couldn't see the SIP traffic come into their border router. SIP traffic coming from SIP provider to the affected customer came through fine. It's just Us -> SIP server was a problem. I thought there may be some strange BGP issue going on but we had other customers within the same /24 as the affected customers and they were connecting fine. The traffic at the time traversed Our network -> Qwest/century link -> Level 3 -> SIP provider I changed the routing around so it would go through our other upstream, AT&T, and it started working. With AT&T, the route was Our network -> AT&T -> Level 3 -> SIP provider So my questions is, is it possible there is some kind of filter at Qwest or Level 3 that is dropping traffic only for udp 5060 for select few IPs? That's the only explanation I can come up with other than the whole Juniper BGP issue 2 days ago left something in between in a strange state? I read the post about XO doing filtering on transit traffic, I haven't seen anyone say Level 3 or Qwest is doing the same.