[29352] in North American Network Operators' Group
Re: Jumbo Frames (was Re: MAE-EAST Moving? from Tysons corner toreston VA. )
daemon@ATHENA.MIT.EDU (Bill Woodcock)
Mon Jun 19 12:33:04 2000
Date: Mon, 19 Jun 2000 09:28:33 -0700 (PDT)
From: Bill Woodcock <woody@zocalo.net>
To: William Allen Simpson <wsimpson@greendragon.com>
Cc: nanog@merit.edu
In-Reply-To: <394E45CA.B60502DD@greendragon.com>
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Errors-To: owner-nanog-outgoing@merit.edu
> Which is one of the reasons that we specified 1600 as the frame size
> for most line disciplines, such as PPP over Frame Relay, etc., since
> circa 1992....
> PPP itself is 1500, matching ethernet, in the vain hope that folks
> would remember to distinguish "packet" data size from "frame" size.
This problem is also one that plagues DSL, as many DSLAMs expect to see a
full Ethernet packet, including Ethernet header, inside the frame/atm
packet that comes in from the network. They strip the frame/atm header,
and dump the contents onto the DSL/Ethernet wire.
If you're using frame relay on the backhaul, a max-length Ethernet packet
with both Ethernet and frame relay headers will obviously exceed the
1500-byte limit, and get truncated. If you pull the Ethernet header out,
you need to get the DSLAM to generate a new one on the other side, which
many of them verge on not being smart enough to do.
-Bill
