Messages in this thread | | | Subject | Re: MTU and 2.4.x kernel | Date | Thu, 15 Feb 2001 21:01:21 +0000 (GMT) | From | Alan Cox <> |
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> > I ran DNS reliably over AX.25 networks. They have an MTU of 216. They work. > > 512 is maximal message size, which is transmitted without troubles, > hardwired to almost all the datagram protocols.
Message size != MTU. DNS doesnt use DF. In fact DNS can even fall back to TCP.
> > > B. Accoutning, classification, resource reervation does not work on > > > fragmented packets. > > Thats a bug in accounting classification and resource reservation. > Sorry? It is bug in client mtu selection. Functions above are impossible > on fragmented packet even in theory. And because of A, if client uses mtu > 296, it cannot use 100% of emerging and existing IP functions.
Tragic. You are required to accept existing realities and degrade nicely.
> > Over a 9600 mobile phone link mtu 296 makes measurable differences to the > > latency when mixing a mail fetch with typing. > > It is myth. Changing mtu until ~4K does not affect latency, it stays on 4K/bw.
Please tell that to my phone.
> > Over a radio link where > > error rate causes exponential increases in probability of packet loss as > > Another myth. All they do error correction and have so high latency, > that _increasing_ mtu only helps. And helps a lot.
No. There is large amounts of real world hardware that this is not true for. You cannot do good FEC on a narrow band link.
Alan
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