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Commit 14f3ad6f authored by Ulrich Weber's avatar Ulrich Weber Committed by David S. Miller
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ipv6: Use 1280 as min MTU for ipv6 forwarding 



Clients will set their MTU to 1280 if they receive a
ICMPV6_PKT_TOOBIG message with an MTU less than 1280.

To allow encapsulating of packets over a 1280 link
we should always accept packets with a size of 1280
for forwarding even if the path has a lower MTU and
fragment the encapsulated packets afterwards.

In case a forwarded packet is not going to be encapsulated
a ICMPV6_PKT_TOOBIG msg will still be send by ip6_fragment()
with the correct MTU.

Signed-off-by: default avatarUlrich Weber <uweber@astaro.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fbf219f1

net/ipv6/ip6_output.c

+8 −4
Original line number Diff line number Diff line
@@ -402,6 +402,7 @@ int ip6_forward(struct sk_buff *skb) 
	struct ipv6hdr *hdr = ipv6_hdr(skb);

	struct inet6_skb_parm *opt = IP6CB(skb);

	struct net *net = dev_net(dst->dev);

	u32 mtu;



	if (net->ipv6.devconf_all->forwarding == 0)

		goto error;
@@ -508,10 +509,14 @@ int ip6_forward(struct sk_buff *skb) 
		}

	}



	if (skb->len > dst_mtu(dst)) {

	mtu = dst_mtu(dst);

	if (mtu < IPV6_MIN_MTU)

		mtu = IPV6_MIN_MTU;



	if (skb->len > mtu) {

		/* Again, force OUTPUT device used as source address */

		skb->dev = dst->dev;

		icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, dst_mtu(dst));

		icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);

		IP6_INC_STATS_BH(net,

				 ip6_dst_idev(dst), IPSTATS_MIB_INTOOBIGERRORS);

		IP6_INC_STATS_BH(net,
@@ -621,8 +626,7 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *)) 
	mtu = ip6_skb_dst_mtu(skb);



	/* We must not fragment if the socket is set to force MTU discovery

	 * or if the skb it not generated by a local socket.  (This last

	 * check should be redundant, but it's free.)

	 * or if the skb it not generated by a local socket.

	 */

	if (!skb->local_df) {

		skb->dev = skb_dst(skb)->dev;