[Olsr-dev] mtu problem with multicast ipv6 packets

Kaplan L. Aaron (spam-protected)
Sun Oct 19 21:41:08 CEST 2008

I believe there was also once an issue with MTU sizes on different  
(jumbo?) wifi links.

thanks for the patch!

On Oct 19, 2008, at 9:30 PM, John Hay wrote:

> Hi,
> While debugging some other stuff, I noticed that a lot of the olsr  
> packets
> on our network was fragmented. Looking into it a bit, it turns out  
> that
> while the interface mtu might be 1500 bytes, on FreeBSD (and I  
> would guess
> most other BSDs) by default multicast IPv6 packets will be  
> transmitted with
> a mtu of 1280 bytes. RFC 3542 Section 11.1 gives the reasoning  
> behind it.
> So here is my patch to clip the mtu in the IPv6 case. I have hardcoded
> OLSR_IPV6_MTU, but at least on the BSDs it is defined in netinet/ 
> ip6.h as
> IPV6_MMTU. It did not look as if ip6.h is pulled in at the moment,  
> so I did
> not know if we should start now. :-)
> John
> -- 
> John Hay -- (spam-protected) / (spam-protected)

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