Re: [tcpdump-workers]tcpdum lose packets

[Guy Harris <guy () alum mit edu>]

On Jan 12, 2009, at 11:09 PM, liu.yongfeng () zte com cn wrote:

> I use tcpdump to capture the packets of one RTP stream  in my rtsp
> server,

So you're running tcpdump on the server, trying to capture the traffic  
on that RTP stream?

If that's true, what filter are you using when you're capturing?  Or  
are you trying to capture *all* the traffic to and from the server?

> by the RTP sequence number,i found some packets had lost.
> but in the client that conneted to this server in the same time ,use
> tcpdump capture the packets of this RTP stream,

So, in that case, you're running TCP on the client, trying to capture  
the traffic on the same stream?

If that's true, what filter are you using when you're capturing?  Or  
are you trying to capture *all* the traffic to and from the client?

> i do not found lost packet.i don't konw why?

If you're not using a filter when you're capturing, the problem could  
be that your server has more traffic going to and from it than your  
client does, so if you're capturing *all* the traffic to or from the  
server, that requires more kernel buffer memory, more CPU, and more  
disk bandwidth than if you're capturing all the traffic to or from the  
client.

Unfortunately, RTP doesn't use fixed port numbers, so it's hard to set  
up a filter to capture all the traffic on an RTP stream.
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