Re: [PATCH 2/2] ipvs: Extend MTU check to account for IPv6 NAT defrag changes

Julian Anastasov
2012-08-28T09:47:40Z

Hello,

On Tue, 28 Aug 2012, Jesper Dangaard Brouer wrote:

> On Mon, 2012-08-27 at 18:20 +0300, Julian Anastasov wrote:
> >
> > > @@ -956,8 +963,11 @@ ip_vs_tunnel_xmit_v6(struct sk_buff *skb, struct ip_vs_conn *cp,
> > > skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
> > >
> > > /* MTU checking: Special for tunnel mode */
> > > - if (mtu < ntohs(old_iph->payload_len) + sizeof(struct ipv6hdr) &&
>
> I guess:
> ntohs(old_iph->payload_len) + sizeof(struct ipv6hdr)
> Is the same as:
> skb->len

I think so. You can think of this in different way:
all transmitters are called from same place, there is no
difference in the packets we see. When we can use
__mtu_check_toobig_v6 for other methods relying on skb->len
being correct, we can do the same for tunnels, only that
tunnels have lower MTU, that is the only difference.

> > > - !skb_is_gso(skb)) {
> > > + if ((!IP6CB(skb)->frag_max_size &&
> > > + (mtu < ntohs(old_iph->payload_len) + sizeof(struct ipv6hdr) &&
> > > + !skb_is_gso(skb)))
> > > + || IP6CB(skb)->frag_max_size + sizeof(struct ipv6hdr) > mtu) {
>
> >
> > mtu is already reduced with the new outer header size,
> > may be we can just call __mtu_check_toobig_v6 with mtu?
>
> To Julian, is the extra sizeof(struct ipv6hdr) addition to
> frag_max_size, wrong? (as the mtu is already reduced)

Yes, sizeof(struct ipv6hdr) is needed only together
with payload_len because payload_len does not include the
first header.

> If above statements hold, I think we can simply use
> __mtu_check_toobig_v6() also for the tunnel case :-)

Yep

> --Jesper

Regards

--
Julian Anastasov <ja@ssi.bg>