[Cerowrt-devel] Fwd: [PATCH] ag71xx: Added support for baby-jumbo packets.

dpreed at reed.com dpreed at reed.com
Sat Jun 23 18:33:14 EDT 2012

All true, but most TCP's these days support Path MTU discovery, and most apps that can use > 1500 bytes test the path before using, even if using UDP.

Setting lower MTUs on a home network, etc. is useful only if the large MTUs are problematic on the links involved.   A 9k MTU is bad on a 128k ISDN link, for sure.

Preserving legacy limits because there were problems with them 5 years ago is a sure way to lock yourself in to problems.   Drivers shouldn't have the limits compiled in, instead you can use commands to shrink MTU if need to do so exists.

-----Original Message-----
From: "Robert Bradley" <robert.bradley1 at gmail.com>
Sent: Saturday, June 23, 2012 5:47pm
To: cerowrt-devel at lists.bufferbloat.net
Subject: Re: [Cerowrt-devel] Fwd: [PATCH] ag71xx: Added support for baby-jumbo packets.

On 23/06/12 20:29, dpreed at reed.com wrote:
> I find it curious that packet aggregation is done in 802.11n standards, but that the packets are limited to 1540.   I bet that limit may not be there in all Atheros NICs, and maybe not in this one.  Will investigate now that I'm curious.

The patch only affects the wired Ethernet driver, so 802.11n packet 
aggregation does not apply here.  TSO and friends could apply in theory, 
but either is unsupported or disabled in this case.  The wireless side 
is handled by the ath9k driver instead, where I know nothing about the 
upper limits on MTU.  Depending on the cards used by the clients, the 
maximum MTU may be limited to 1500 even if the ath9k driver can cope.
Robert Bradley
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