Re: disabling checksums flag

[alex medvedev <alexm () pycckue org>]

Hi Hannes,

i like checksumming and i think this functionality is great and
informative.
the reason i tried to disable the checksumming was unpleasant messages
[bad tcp cksum!] and [bad cksum!] while running over loopback in AIX :)
because AIX does not do checksumming over loopback.

i think you are right that we can simply suppress the warning messages and
still calculate the checksums.

-alexm
--
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On Sat, 19 Jul 2003, Hannes Gredler wrote:

> alex,
>
> could you give some insight why one generally wants to have
> checksumming turned off rather than just turning the
> warning messages off ?
>
> if there are good reasons for both options
> then i'd propose that we still do the checksumming
> verification suppression,based on your flag;
> call it a checksum verification flag ...
>
> i.e.
>
> 12:36:45.587565 OSI, IS-IS, length: 405
>         hlen: 27, v: 1, pdu-v: 1, sys-id-len: 6 (0), max-area: 3 (0), pdu-type: L2 LSP
>           lsp-id: 2092.1113.4009-00, seq: 0x000002fd, lifetime:  1198s
>           chksum: 0xe984 (correct), PDU length: 405, L1L2 IS
>                          ^^^^^^^^^
> becomes with k flag
>
> 12:36:45.587565 OSI, IS-IS, length: 405
>         hlen: 27, v: 1, pdu-v: 1, sys-id-len: 6 (0), max-area: 3 (0), pdu-type: L2 LSP
>           lsp-id: 2092.1113.4009-00, seq: 0x000002fd, lifetime:  1198s
>           chksum: 0xe984, PDU length: 405, L1L2 IS
>
> /hannes
>
> On Fri, Jul 18, 2003 at 12:55:50PM -0500, alex medvedev wrote:
> | hallo,
> |
> | i would like to add a disable checksum flag to tcpdump.
> |
> | i assume this will affect ip, tcp, udp, icmp, icmp6, isoclns, igmp, vrrp,
> | mobile printers, and tcpdump.c file (is it all?)
> |
> | proposed change:
> | add a global int cksumflag=1 in tcpdump.c :)
> | add a command line flag: k (?),
> | which when specified disables the checksum calculation (cksumflag=0);
> | check cksumflag before calculating checksums in printers.
> |
> | i attached the patch against today's cvs, which worked on my setup,
> | but i have no idea what some printers do, so, please, let me know
> | if there is more changes needed or things should be done differently.
> |
> |  ???
> |
> | thanks,
> |
> | -alexm

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