RE: [RPRWG] RE: [IPORPR] payload length and padding and stuff
Dan -
If your question translates as "Can a Bridge be built that supports
more than one type of MAC", then the answer is Yes. And indeed,
there are Bridges that support plug-in blades for each port, and which
can therefore potentially support a wide variety of frame
sizes.
However, at least as far as the standard is concerned, there is no
configurable per-Port parameter involved; if a Port supports an 802.X
MAC, then the frame size supported on that Port is as stated in the
standard for the 802.X MAC (i.e., there is no standard means to
configurable the frame size independently of the MAC type).
So, if you are asking "Is it possible to build a Bridge that will
forward jumbo frames?" then clearly, the answer is "Yes".
However, that is a different question to asking "Is forwarding jumbo
frames conformant behaviour for a Bridge?"; the interpretation of
the 802.1D standard relative to that question is
"No".
Regards,
Tony
At 10:34 09/12/2002 +0200, Romascanu, Dan (Dan) wrote:
Tony,
You are right, and I obviously
stand corrected. My question would be - is the reference
mac_service_data_unit supported by the LAN configurable per port? If the
answer is yes, the implication would be that standard 802.1D bridges can
be configured to support these MAC and PHY implementations that
accommodate larger frame sizes ('jumbo frames') that some vendors built
as proprietary extensions to the 802.3 MAC and PHYs.
Regards,
Dan
- -----Original Message-----
- From: Tony Jeffree
[mailto:tony@xxxxxxxxxxxxx]
- Sent: Thursday, December 05, 2002 11:36 AM
- To: Romascanu, Dan (Dan)
- Cc: Nader Vijeh; iporpr@xxxxxxxx; stds-802-17@xxxxxxxx
- Subject: RE: [RPRWG] RE: [IPORPR] payload length and padding and
stuff
- Dan -
- I think that you will find the 802.1D standard requires conformant
Bridges to discard frames that exceed the max frame size for the
destination LAN:
- "7.7.1 Enforcing topology
restriction
- Each Port is selected as a potential transmission Port if, and only
if
- a) The Port on which the frame was received was in a forwarding state
(8.4), and
- b) The Port considered for transmission is in a forwarding state,
and
- c) The Port considered for transmission is not the same as the Port
on which the frame was received,
- and
- d) The size of the mac_service_data_unit conveyed by the frame does
not exceed the maximum size of
- mac_service_data_unit supported by the LAN to which the Port
considered for transmission is
- attached.
- For each Port not selected as a potential transmission Port, the
frame shall be discarded."
- Regards,
- Tony
- At 18:25 04/12/2002 +0200, Romascanu, Dan (Dan) wrote:
- Nader,
- There are actually two different layers here.
- 802.3 MACs and PHYs MUST support a max frame length of 1522. You may
find implementations that are both standard compliant and support jumbo
sizes as proprietary extensions.
- I think that 802.1 bridges do not have such a limitation within the
standard. As you mention, they can be configured to support larger frame
sizes. Actually some of the non-Ethernet 802 technologies already support
larger frame sizes.
- Dan
- > -----Original Message-----
- > From: Nader Vijeh
[mailto:nader@xxxxxxxxxxxxxx]
- > Sent: Wednesday, December 04, 2002 6:10 PM
- > To: Romascanu, Dan (Dan)
- > Cc: iporpr@xxxxxxxx; stds-802-17@xxxxxxxx
- > Subject: RE: [RPRWG] RE: [IPORPR] payload length and padding and
stuff
- >
- >
- > Dan,
- >
- > Thank you for the correction. Jumbo frames are not supported
- > by the 802.3
- > standard.
- > There are Ethernet switches on the market that support jumbo
- > frames in a
- > proprietary manner. Of course these will not interoperate
- > with standard
- > compliant 802.1 bridges. As I pointed out in the rest of the
- > message, even
- > if jumbo frames are supported, max frame size "needs to be
- > configurable to
- > be lower, in order to comply with transparent bridging
requirements".
- >
- > Nader
- >
- > -----Original Message-----
- > From: Romascanu, Dan (Dan)
[mailto:dromasca@xxxxxxxxx]
- > Sent: Wednesday, December 04, 2002 12:45 AM
- > To: Nader Vijeh; Necdet Uzun; Anoop Ghanwani
- > Cc: Frank Kastenholz; iporpr@xxxxxxxx; stds-802-17@xxxxxxxx
- > Subject: RE: [RPRWG] RE: [IPORPR] payload length and padding and
stuff
- >
- >
- > >
- > > The max frame size may be extended beyond 802.3 1522 bytes
- > > limit as there is
- > > precedence in 802.3 community.
- >
- > Nader,
- >
- > I am not sure what you exactly mean. If you refer to what is
- > popularly known
- > as 'Jumbo frames', they are not supported by the IEEE 802.3
- > standards.
- >
- > Dan
- >
- Regards,
- Tony
Regards,
Tony