title: Capturing on a non-default interface with tcpdump
body: <p>O/P of if config is </p>
  
  <pre><code>[root@test2 ~]# ifconfig
  lo        Link encap:Local Loopback
            inet addr:127.0.0.1  Mask:255.0.0.0
            inet6 addr: ::1/128 Scope:Host
            UP LOOPBACK RUNNING  MTU:16436  Metric:1
            RX packets:3045306 errors:0 dropped:0 overruns:0 frame:0
            TX packets:3045306 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:0
            RX bytes:969363066 (924.4 MiB)  TX bytes:969363066 (924.4 MiB)
  
  p4p1      Link encap:Ethernet  HWaddr F0:4D:A2:F7:CE:20
            inet addr:192.168.250.58  Bcast:192.168.250.255  Mask:255.255.255.0
            inet6 addr: fe80::f24d:a2ff:fef7:ce20/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
            RX packets:222163621 errors:0 dropped:0 overruns:0 frame:0
            TX packets:29525032 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:1000
            RX bytes:67504475609 (62.8 GiB)  TX bytes:13910424527 (12.9 GiB)
  
  virbr0    Link encap:Ethernet  HWaddr 52:54:00:3C:38:60
            inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
            RX packets:0 errors:0 dropped:0 overruns:0 frame:0
            TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:0
            RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
  </code></pre>
  
  <p>when i executed tcpdump , o/p is </p>
  
  <pre><code>root@test2 ~]# tcpdump
  tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
  listening on virbr0, link-type EN10MB (Ethernet), capture size 65535 bytes
  </code></pre>
  
  <p>where it is listening to vibra0 interface as default.
  I want to set p4p1 interface as default interface so that i may get appropriate o/p when executing tcpdump.</p>
  
  <p>Any solutions.</p>