Re: aix: tcpdump over loopback

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

On Monday, July 7, 2003, at 4:11 PM, alex medvedev wrote:

> is there an easy way to find out the current linktype in print-ip.c?

Not really - "main()" doesn't save the link type in a global variable, 
and the pcap_t from which tcpdump is reading isn't global.

> AIX doesn't compute cksum over loopback.
> i would like to add a check, so that if we are listening on a loopback,
> i.e. linktype == IFT_LOOP we simply do not compute/print cksum but 
> still
> compute it on other link types.

Other OSes *do* compute a checksum on loopback interfaces, so that's 
not necessarily the right thing to do.

Furthermore, the checksums are invalid on outgoing packets on 
interfaces that do checksum offloading, so that shouldn't be restricted 
to loopback interfaces.

The right thing to do is probably to add a command-line flag to turn 
off checksum checks (I think somebody suggested that at one point).

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