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

Robert Bradley robert.bradley1 at gmail.com
Fri Jun 22 16:41:38 EDT 2012

On 22/06/12 21:11, dpreed at reed.com wrote:
> Good step.  Why not allow 9K byte jumbos when one's packets traverse a path that is internal to the local area, and all the 1 GigE links support 9K?

All the posts I could see claim that the System-on-Chip NIC (Atheros 
AR7161) cannot handle packets greater than 1540 octets, so routing 9k 
packets from wired->wireless or wired->WAN would not be an option.  If I 
understood Dave's previous post correctly, though, the built-in switch 
allows jumbo packets, so wired->wired internal traffic should work fine 
with 9K packets already.

The only issue with that setup is that with mismatched MTUs, it might be 
impossible to communicate with the router and the 9k-friendly nodes at 
the same time.  Thankfully, on Linux at least, you can set per-route 
MTUs (http://lartc.org/howto/lartc.cookbook.mtu-discovery.html), so it 
might be possible to exploit that to do what you want.  Maybe something 
like this would work?

ip route add default via mtu 1500
ip route add dev eth0 mtu 1500
ip route add dev eth0 mtu 9000

Robert Bradley

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