Re: RUNT Packets(Last Word)
I am not proposing anything and have little interests keeping this discussion
going. The whole thing was started with a EOP question for XGMII interface.
I am simply saying It's not a good idea for MAC for to discard a receiving
carrier event with good preamble and SFD without saying anything. If the
standard board doesn't think this is a standard issue and it's implementation
dependent. I have no problem with that. But, If "The MAC silently discards
packets that are shorter than the minimum", than who is telling RMON
to increase those counters. As far as I know, MAC is the only device checking
Preamble, SFD, FCS and frame byte counts.
Shimon was right, whatever in the standard now didn't prevent us from doing
the right thing. I don't think it will in the future.
> We are writing a standard and need to keep focused on what is in scope for
> the standard to define.
> The MAC defined in 802.3 doesn't forward a packet to the host until it has
> checked. Of course, some implementations may start forwarding the packet
> earlier, but providing some mechanism to cause discard of an errored frame
> that the MAC has started to forward is an implementation issue for those
> MACs and not an 802.3 issue.
> The MAC defined in 802.3 also does not take any action with an undersized
> frame other than discard it. It does not do any counter update for an
> undersized frame. We haven't changed this aspect of the MAC definition. It
> has been this way always. Of course, an implementation or an IETF management
> standard such as RMON is always free to add additional managed objects that
> cover items we did not put in the 802.3 MAC decision. In that case, it is up
> to the implementor or the IETF folks to define the way that object works.
> The alternative is for someone to propose adding the object to 802.3
> I do not see why we are continuing to discuss this subject. Are you
> proposing some action for 802.3ae?
> -----Original Message-----
> From: Louis Lin [mailto:louislin@xxxxxxxx]
> Sent: Thursday, November 16, 2000 2:20 PM
> Cc: stds-802-3-hssg@xxxxxxxx
> Subject: Re: RUNT Packets
> I have to disagree with your statement of "The MAC silently discards packets
> that are shorter than the minimum". When MAC is receiving a packet and
> forwarding the packet data to the host. If the the EOP comes before 64th
> MAC needs to inform host to discard the packet and that packet needed to be
> counted in RMON. Otherwise we will see packets disappear(packet counts
> mis-match) if they are shortened by what ever reasons.
> Standard doesn't need to say anything about it, but saying "The MAC silently
> discards packets that are shorter than the minimum" is not good. And I
> believe most MACs in the market count undersized packets.
> Of course, most undersized packets don't come with good CRC. But we can't
> make this kind of assumption.
> Shimon Muller wrote:
> > > The important point is that runts are not counted by MACs.
> > > The MAC silently discards packets that are shorter than the minimum.
> > > It has no counter for them.
> > Pat is absolutely correct.
> > > Unless someone is proposing creating a new runt MIB object, runts do not
> > > apply to 10 Gig Ethernet because we do not have repeaters.
> > I do not believe we should create such an object.
> > Just ignore the "shortened" frame. This is not something that is expected
> > to happen very often. And if it does, there are going to be other errors
> > that will give you plenty of indication that something is broken.
> > Shimon.