Jumbo Frames -- How do they work?

Jumbo Frames -- How do they work?

Post by Thomas Bahl » Sun, 06 Jul 2003 01:08:40



Hi all,

Recently I had spent a minute on how Ethernet Jumbo Frames (i.e.,
something around 9k) would work. I understand that there is no standard
for it and the technology was originally driven by Alteon, now Lucent.
Unfortunately, their White Paper has vanised from the Web and I didn't
find much more technical information.

What I am struggeling with is how the frame format of a Jumbo Frame would
look like. So far, 0x0600 has been the hard limit that determines type or
length encapsulation. 9k is certainly beyond 0x0600 and would, therefore,
be regarded as type instead of length.

Could anybody share some more insights with me how Jumbo Frames look like
and how that feature works? At cisco.com I read something about
negotiation but with no further details.

Thanks,
/Tom.

--
Thomas Bahls                | "Wege enstehen dadurch, da? man sie geht."
Greifswald, Germany         |                             -- Franz Kafka
http://tbahls.gmxhome.de/   |

 
 
 

Jumbo Frames -- How do they work?

Post by Albert Manfred » Tue, 08 Jul 2003 06:43:35



> Recently I had spent a minute on how Ethernet Jumbo Frames (i.e.,
> something around 9k) would work. I understand that there is no
standard
> for it and the technology was originally driven by Alteon, now
Lucent.
> Unfortunately, their White Paper has vanised from the Web and I
didn't
> find much more technical information.

> What I am struggeling with is how the frame format of a Jumbo
Frame would
> look like. So far, 0x0600 has been the hard limit that determines
type or
> length encapsulation. 9k is certainly beyond 0x0600 and would,
therefore,
> be regarded as type instead of length.

Agreed. Jumbo frames must use "type" encapsulation.

Quote:> Could anybody share some more insights with me how Jumbo Frames
look like
> and how that feature works? At cisco.com I read something about
> negotiation but with no further details.

Not sure there's anything more to tell, but Id love to know if I'm
missing anything. As long as every Ethernet switch along the way
knows that 9K frames are allowable, and you're using "type"
encapsulation, all should work perfectly well.

RFC 1191, MTU Discovery, works by setting the "do not fragment" bit,
then a source sending bigger and bigger frames until it gets back a
ICMP error message. I would think that basic mechanism ought to work
when jumbo frames are allowed by switches and routers?

Bert

 
 
 

1. Jumbo Ethernet Frames and PIX

    Hello all,

    I'm configuring a PIX 535 with two GBEthernets, one side terminates onto
a 6509 which will have MSFC-2s, and the other onto a 4003. I'd like to
enable Jumbo frames on the switch ports of each respective switch and on the
535s, as well. Has anybody attempted this? If so, can you share with me the
results?

    TIA

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