# Re: \[PATCH 02/19\] Cleaning up the IPv6 MTU checking in the IPVS xmit code, by using a common helper function \_\_mtu\_check\_toobig\_v6().

- From: Jesper Dangaard Brouer \<hidden\>
- Date: 2012-08-29 08:02:37 
- List: netdev
- Page: https://ratatoskr.run/netdev/2012/08/10902853
- Thread: https://ratatoskr.run/netfilter-devel/2012/08/10902833/t.md

```text

Just a little nitpick.

The original title/subj was:
 "ipvs: IPv6 MTU checking cleanup and bugfix"

And the curr/used title/subj were part of the commit text.


On Tue, 28 Aug 2012, Patrick McHardy wrote:

> From: Jesper Dangaard Brouer <redacted>
>
Insert:
 Cleaning up the IPv6 MTU checking in the IPVS xmit code, by using a
 common helper function __mtu_check_toobig_v6().

> The MTU check for tunnel mode can also use this helper as
> ntohs(old_iph->payload_len) + sizeof(struct ipv6hdr) is qual to
> skb->len.  And the 'mtu' variable have been adjusted before
> calling helper.
>
> Notice, this also fixes a bug, as the the MTU check in ip_vs_dr_xmit_v6()
> were missing a check for skb_is_gso().
>
> This bug e.g. caused issues for KVM IPVS setups, where different
> Segmentation Offloading techniques are utilized, between guests,
> via the virtio driver.  This resulted in very bad performance,
> due to the ICMPv6 "too big" messages didn't affect the sender.
>
> Signed-off-by: Jesper Dangaard Brouer <redacted>
> Signed-off-by: Patrick McHardy <redacted>
> ---
> net/netfilter/ipvs/ip_vs_xmit.c |   21 +++++++++++++++------
> 1 files changed, 15 insertions(+), 6 deletions(-)

[cut]

Hilsen
  Jesper Brouer

--
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MSc. Master of Computer Science
Dept. of Computer Science, University of Copenhagen
Author of http://www.adsl-optimizer.dk
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```