Re: Intel X520-SR2 not seeing packets in tcpdump

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

On Mar 1, 2012, at 3:39 PM, Mark W. Jeanmougin wrote:

> On Thu, Mar 1, 2012 at 11:55, Charles DeVoe <scarecrow_57 () yahoo com> wrote:
> > I have installed an X520 card with the latest driver ixgbe 3.8.  The operating systems is CentOS 5.7.  When doing an 
> > ifconfig I see receive packets.  I also see packets when I do an ethtool -S p1p2.  However, when I do tcpdump -i 
> > p1p2 I see no packets.  Does anyone know why this may be happening.
> > -
>
> Charles,
>
> I've got some experience with the X520 cards under various flavors of
> Linux. I've always had good luck. Although, they do require a bit more
> care and feeding than a Copper e1000. Can you be a bit more specific
> about what you're seeing?
>
> The other thing I'll throw out there: Do you have vlan tags set on
> these packets? If so, you need to add the "vlan" option to tcpdump.

That should only be necessary if you're capturing with a filter; if the command is just

        tcpdump -i p1p2

then no filter was specified, so "vlan" shouldn't be necessary and will, in fact, *reduce* the number of packets (as 
it'll mean capturing only packets with VLAN tags).

"vlan" is used when its side-effect, of causing other filters to go past the VLAN tag and look at the actual Ethernet 
type field, is desired, e.g. if you have tagged packets, "host foobar" won't work as it won't recognize IPv4 or IPv6 
packets, you'd need either

        vlan and host foobar

or

        host foobar or vlan and host foobar

where the former will match only VLAN-tagged packets to or from "foobar" and the latter will match untagged or 
VLAN-tagged packets to or from "foobar".

(I.e., "vlan" isn't an option, it's a term to use in a filter expression.)-
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