ipv6: Use 1280 as min MTU for ipv6 forwarding (14f3ad6f) · Commits · 戴 / test

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:

Ulrich Weber <uweber@astaro.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

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;

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