Re: MTUs - Was: Strange public traceroutes return private RFC1918 addresses
So there we are. Want to bet on whether 40 GigE will still have the 1522 byte limit? Given the growing number of folks who will only buy xGigE equipment that supports 9000 byte MTUs I'd say the chances are very good that 40GigE will no longer have a 1522 byte limit. --Michael Dillon
Re: MTUs - Was: Strange public traceroutes return private RFC1918 addresses
On 6-feb-04, at 11:24, [EMAIL PROTECTED] wrote: So there we are. Want to bet on whether 40 GigE will still have the 1522 byte limit? Given the growing number of folks who will only buy xGigE equipment that supports 9000 byte MTUs I had that happen one time: when evaluating some gigE switches a few years ago I complained that they would only do 1500 bytes. A week later they had new boards that did 64k for me. :-) I'd say the chances are very good that 40GigE will no longer have a 1522 byte limit. I don't think vendors are going to risk building 40GE stuff that can only do 1500, but the IEEE on the other hand would look pretty stupid by giving in at 40G after sticking to 1500 at 1 and 10.
Re: MTUs - Was: Strange public traceroutes return private RFC1918 addresses
So there we are. Want to bet on whether 40 GigE will still have the 1522 byte limit? Given the growing number of folks who will only buy xGigE equipment that supports 9000 byte MTUs I'd say the chances are very good that 40GigE will no longer have a 1522 byte limit. strange planet you live on. ieee decisions are just not made that way. randy
Re: MTUs - Was: Strange public traceroutes return private RFC1918 addresses
From: Warren Kumari [EMAIL PROTECTED] Date: Thu, 5 Feb 2004 15:04:00 -0500 Sender: [EMAIL PROTECTED] Ok, I know that this is getting away from the original thread, but I've always wondered this... Why is the MTU on Ethernet 1500 bytes? I have looked through various docs (eg IEEE Std 802.x) and can find where maxUntaggedFrameSize is listed as 1518 octets, but there is no mention of why this was chosen. I know where the minimum frame size comes from (CSMA/CD and propagation times, etc), but the maximum frame size number sounds fairly arbitrary. It is based on the original 10Base5 (yellow hose) Ethernet and was largely picked out of the air to meet several design criteria. One was the cost of buffering on the card. Back then, 2K of buffer was expensive and the designers wanted to allow for $500 NICs. This was in the late 1970s and this was no trivial feat. Early Ethernet cards were several K and taps were typically over $200. And that awful AUI cable that always came loose (the designer has publicly apologized for that) was usually at least $50. Another issue was how long a system with a packet ready to transmit might have to wait for a transmission to end so that it could have a shot at the wire. (Remember that in the 10Base5 days it was not uncommon to see 50 or 100 taps on a single cable.) At 10 Mb/s, long frames would have been prohibitively time consuming. Also, a large percentage of network traffic in these pre-web days was telnet with huge numbers of 64 byte frames and few over 1K. So 1518 seemed reasonable. When FastEthernet was developed by Grand Junction, the idea of expanding the frame size first came up. At 100 Mb/s, 1500 bytes no longer took very long. But that made for problems in bridging between 10Base5 and 100Base-T networks. There was no good way to break up a 4K frame into 1518 byte frames in a switch and, while many schemes were suggested none proved practical and the idea faded. Then came GigE and 1518 bytes was getting to look very silly. But the issues of bridging and fragmentation remained and, after LOTS of debate, the 1518 byte frame limit was left in place. But the idea did not die and many companies started producing equipment that could handle larger frame sizes. It worked pretty well because most GigE links were point-to-point between end systems switching to slower speed links less common. Finally we got to 10GigE and 1522 (extended for vLANs) was absolutely ridiculous, but at least one large vendor fought had to retain the size and, in the end, the 10GigE spec specified the same maximum frame size. The only reason now was cost. At 10GigE, buffers already had to be very big as a great many frames had to be stored just to handle normal traffic was congestion. Some vendors were selling relatively cheap switches with VERY limited buffering. To move from 1520 to 4K or 9K would have required a significant increase in buffer size and that would have made the switches much more expensive. So there we are. Want to bet on whether 40 GigE will still have the 1522 byte limit? -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: [EMAIL PROTECTED] Phone: +1 510 486-8634
Re: MTUs - Was: Strange public traceroutes return private RFC1918 addresses
Warren Kumari wrote: Ok, I know that this is getting away from the original thread, but I've always wondered this... Why is the MTU on Ethernet 1500 bytes? I have looked through various docs (eg IEEE Std 802.x) and can find where maxUntaggedFrameSize is listed as 1518 octets, but there is no mention of why this was chosen. I know where the minimum frame size comes from (CSMA/CD and propagation times, etc), but the maximum frame size number sounds fairly arbitrary. Because that was a conveniently large amount of very pricey memory availble at the time? Because that was the amount that could be blatted down a 500 meter hose and get the CD part to work at some common clock rate?
Re: MTUs - Was: Strange public traceroutes return private RFC1918 addresses
Kevin Oberman wrote: So there we are. Want to bet on whether 40 GigE will still have the 1522 byte limit? What was the last year that automobiles had the fitting for a crank on the front of the engine? (My recollection is that it was several years after there was hole through the sheetmetal to get to it.)
Re: MTUs - Was: Strange public traceroutes return private RFC1918 addresses
As late as 1973 Dodge Power Wagons (WDX style, at least) still had the aperture and the crankshaft end coupling for a hand crank. Dunno about any later models. David Leonard ShaysNet On Thu, 5 Feb 2004, Laurence F. Sheldon, Jr. wrote: Kevin Oberman wrote: So there we are. Want to bet on whether 40 GigE will still have the 1522 byte limit? What was the last year that automobiles had the fitting for a crank on the front of the engine? (My recollection is that it was several years after there was hole through the sheetmetal to get to it.)
Re: MTUs - Was: Strange public traceroutes return private RFC1918 addresses
M. David Leonard wrote: As late as 1973 Dodge Power Wagons (WDX style, at least) still had the aperture and the crankshaft end coupling for a hand crank. Dunno about any later models. Kind of my point--I doubt that you could actually crank one to start it (just guessing here--high-compression V8?) And further, I'm guessing it would be a widow-maker if you tried. But that was the way it had always been done Yes, I know--not operational and all--I'll drop it here.
