Wireshark · Ethereal-users: Re: [Ethereal-users] Packet trace question- are invaild checksums "bad"

[Ulf Lamping <ulf.lamping@xxxxxx>]

Phil Jannusch wrote:

>I am starting to trace my network for errors and looking for reasons why
>my LAN is slow.  I am noticing invalid checksums from the NIC on my PC. 
>Is this BAD?  Should I be concerned?
>  
>
You didn't included which checksums you mean, as checksums are used in
different layers of a network protocol stack.

If you get invalid checksums *frequently* from a network card layer
(e.g. Ethernet FCS checksums), you should check your network components
/ cabling.

Seeing wrong Ethernet checksums might just be caused by a
buggy/incomplete driver implementation.

If this is a real problem, you will get frequent retransmissions e.g. at
the TCP layer, which *will* significantly slow down your network.


Invalid checksums in the upper layers may or may not cause problems.


I don't know of any general guideline how many checksum errors may be ok
or not ...

Regards, ULFL