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ip_gre: When TOS is inherited, use configured TOS value for non-IP packets

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A GRE tunnel can be configured so that outgoing tunnel packets inherit
the value of the TOS field from the inner IP header. In doing so, when
a non-IP packet is transmitted through the tunnel, the TOS field will
always be set to 0.

Instead, the user should be able to configure a different TOS value as
the fallback to use for non-IP packets. This is helpful when the non-IP
packets are all control packets and should be handled by routers outside
the tunnel as having Internet Control precedence. One example of this is
the NHRP packets that control a DMVPN-compatible mGRE tunnel; they are
encapsulated directly by GRE and do not contain an inner IP header.

Under the existing behavior, the IFLA_GRE_TOS parameter must be set to
'1' for the TOS value to be inherited. Now, only the least significant
bit of this parameter must be set to '1', and when a non-IP packet is
sent through the tunnel, the upper 6 bits of this same parameter will be
copied into the TOS field. (The ECN bits get masked off as before.)

This behavior is backwards-compatible with existing configurations and
iproute2 versions.

Signed-off-by: David Ward <david.ward@ll.mit.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Ward 2013-01-27 13:04:58 +00:00 committed by David S. Miller
parent 5c766d642b
commit 040468a0a7
1 changed files with 2 additions and 2 deletions
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4
net/ipv4/ip_gre.c
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@ -820,8 +820,8 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
ttl = tiph->ttl;
tos = tiph->tos;
if (tos == 1) {
tos = 0;
if (tos & 0x1) {
tos &= ~0x1;
if (skb->protocol == htons(ETH_P_IP))
tos = old_iph->tos;
else if (skb->protocol == htons(ETH_P_IPV6))