[tcpdump-workers] Latency impact while listening at eth0, lo and any on Linux

[Sergey Gomanyuk]

Hello,

I use pcap library to develop a tool that measures on the fly network latency 
(a time between receiving a request and sending a response) for HTTP, DIAMETER 
and other protocols. My tool is compiled for x86_64 Linux , So I noticed 
significant latency growing if my tool listening traffic at 'any' interface in 
compare with listening at 'eth0'. Listening at 'lo' also increases latency.

So I wander why does latency increase and can I do something to reduce latency 
impact while capturing traffic at 'any' or 'lo' interfaces?

Regards,
Sergey Gomanyuk


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Re: [tcpdump-workers] [tcpdump] tcpdump displays a dot('.') for an Ack flag. (#319)

[Michael Richardson]

pjp> Yesterday while looking through a packet dump, we realised that while
pjp> showing TCP hand shake, tcpdump(8) displays a dot('.') for an
pjp> Acknowledgement flag. The tcpdump(8) manual explains this under the

...

pjp> Why not display letter 'A' for acknowledgement flag? How does this
pjp> dot('.') help??

In general, we attempt to avoid gratuitous changes in output like this.
We are out of options as well.. It was my intention that things like this
would come with a name change to pktdump.  pktdump would use all the same
code, but have a different main(), which different (saner) options, and
different defaults.

So, a patch to change this, optionally by flag in ndo->ndo_NEWFLAG would be
welcome, but I don't think we are going to change the default.

--
]   Never tell me the odds! | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works| network architect  [
] m...@sandelman.ca  http://www.sandelman.ca/|   ruby on rails[

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