title: Multiple active APN
body: <p>I am working with VoLTE capable android devices. When a device attaches to LTE it automatically gets PDN connectivity to APN1 , which is for Internet access. Immediately after that, the device requests PDN connectivity to the IMS APN (APN2). After this procedure completes, the device is connected to two different APNs simultaneously, has different IP addresses for the two APNs and can send traffic simultaneous on both "connections".</p>
  
  <p>Q: I would like to understand how Android (4.1.2 in my case) actually implements this (?)</p>
  
  <p>I assume that these are two different interfaces, but netcfg (adb shell) shows only one interface up, the one for APN1. The one for APN2 is nowhere to be found. It is, however, active and working because the device is sending IMS signalling on it (I am 100% sure of that). As a result, I cannot capture traffic (tcpdump) or add routing rules to ping specific IP addresses via APN2.</p>