From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anders.Franzen@ericsson.com Subject: [RFC] Make the ip6_tunnel reflect the true mtu. Date: Tue, 19 Oct 2010 16:38:43 +0200 Message-ID: <1287499123-25018-1-git-send-email-Anders.Franzen@ericsson.com> Cc: Anders Franzen To: eric.dumazet@gmail.com, netdev@vger.kernel.org Return-path: Received: from mailgw9.se.ericsson.net ([193.180.251.57]:48606 "EHLO mailgw9.se.ericsson.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752229Ab0JSOjE (ORCPT ); Tue, 19 Oct 2010 10:39:04 -0400 Sender: netdev-owner@vger.kernel.org List-ID: From: Anders Franzen The ip6_tunnel always assumes it consumes 40 bytes (ip6 hdr) of the mtu of the underlaying device. So for a normal ethernet bearer, the mtu of the ip6_tunnel is 1460. However, when creating a tunnel the encap limit option is enabled by default, and it consumes 8 bytes more, so the true mtu shall be 1452. I dont really know if this breaks some statement in some RFC, so this is a request for comments. --- net/ipv6/ip6_tunnel.c | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-) diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c index c2c0f89..1f4c3cc 100644 --- a/net/ipv6/ip6_tunnel.c +++ b/net/ipv6/ip6_tunnel.c @@ -1175,6 +1175,8 @@ static void ip6_tnl_link_config(struct ip6_tnl *t) sizeof (struct ipv6hdr); dev->mtu = rt->rt6i_dev->mtu - sizeof (struct ipv6hdr); + if (!(t->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT)) + dev->mtu-=8; if (dev->mtu < IPV6_MIN_MTU) dev->mtu = IPV6_MIN_MTU; @@ -1362,12 +1364,17 @@ static const struct net_device_ops ip6_tnl_netdev_ops = { static void ip6_tnl_dev_setup(struct net_device *dev) { + struct ip6_tnl *t = NULL; + dev->netdev_ops = &ip6_tnl_netdev_ops; dev->destructor = ip6_dev_free; dev->type = ARPHRD_TUNNEL6; dev->hard_header_len = LL_MAX_HEADER + sizeof (struct ipv6hdr); dev->mtu = ETH_DATA_LEN - sizeof (struct ipv6hdr); + t = netdev_priv(dev); + if (!(t->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT)) + dev->mtu-=8; dev->flags |= IFF_NOARP; dev->addr_len = sizeof(struct in6_addr); dev->features |= NETIF_F_NETNS_LOCAL; -- 1.7.2.3