Re: [PATCH 05/19] netfilter: nf_conntrack_ipv6: improve fragmentation handling

Patrick McHardy
2012-08-26T21:20:55Z

On Wed, 22 Aug 2012, Jesper Dangaard Brouer wrote:

> On Sun, 2012-08-19 at 21:44 +0200, Patrick McHardy wrote:
>> On Sun, 19 Aug 2012, Jesper Dangaard Brouer wrote:
>>> On Sat, 2012-08-18 at 14:26 +0200, Patrick McHardy wrote:
> [...]
>
>>> Don't I need to load some of the helper modules, or just the
>>> nf_conntrack_ipv6 module, or perhaps only nf_defrag_ipv6 ?
>>
>> Not with the entire patchset, just IPv6 conntrack is enough. Aith IPv6 NAT
>> the first packet of a connection must always be defragemented, independant
>> of an assigned helper.
>
> When loading "nf_conntrack_ipv6" I run into issues.
>
> When sending a fragmented UDP packet. With these patches, the IPVS
> stack will no longer see the fragmented packets, but instead see one
> large SKB. This will trigger a MTU path check in e.g.
> ip_vs_dr_xmit_v6() and an ICMPv6 too big packet is send back.
>
> IPVS: ip_vs_dr_xmit_v6(): frag needed
>
> Perhaps we could change/fix the MTU check in IPVS?
> (This would also solve issues I've seen with TSO/GSO frames, hitting
> this code path).

I guess this should use the same check as in IPv6 output, check
whether IP6CB(skb)->max_frag_size is != 0 and > MTU and only send
an ICMPv6 error in that case.