Subject: Re: [PATCH] gre: copy ToS/DiffServ bits to outer IP header

From: Stephen Hemminger <[email-masked]>
Date: Mon, 13 Jul 2009 08:33:03 -0700

On Mon, 13 Jul 2009 15:32:25 +0200
Andreas Jaggi <[email-masked]> wrote:

> When tunneling IP traffic with GRE this patch makes it possible to export the
> ToS/DiffServ information to the outer IP header. This is particularly useful in
> a scenario with ESP/AH where the inner IP header is encrypted but the packet
> priority/DiffServ information should still be respected by the transporting
> routers (for example in an MPLS backbone network).
>
> The feature is disabled by default and can be enabled on per-interface basis.
> The flag is stored in an unused bit of ip_tunnel_parm.o_flags, and can be
> modified through the rntl_link interface.

Why make it an option? Sounds like it should always be on.

> Also does this bring Linux back in the game, as JunOS/IOS provide this for
> quite some time:
> http://www.cisco.com/en/US/docs/ios/11_3/feature/guide/greqos.html
> http://www.juniper.net/techpubs/software/junos/junos94/swconfig-services/configuring-a-gre-tunnel-to-copy-tos-bits-to-the-outer-ip-header.html
> 
> Signed-off-by: Andreas Jaggi <[email-masked]>
> 
> diff -urN vanilla-linux-2.6.29.4/include/linux/if_tunnel.h dev-gre/include/linux/if_tunnel.h
> --- vanilla-linux-2.6.29.4/include/linux/if_tunnel.h	2009-05-19 01:52:34.000000000 +0200
> +++ dev-gre/include/linux/if_tunnel.h	2009-07-13 15:15:26.000000000 +0200
> @@ -24,6 +24,7 @@
>  #define GRE_REC		__constant_htons(0x0700)
>  #define GRE_FLAGS	__constant_htons(0x00F8)
>  #define GRE_VERSION	__constant_htons(0x0007)
> +#define GRE_COPY_TOS	__constant_htons(0x0008)
>  
>  struct ip_tunnel_parm
>  {
> diff -urN vanilla-linux-2.6.29.4/net/ipv4/ip_gre.c dev-gre/net/ipv4/ip_gre.c
> --- vanilla-linux-2.6.29.4/net/ipv4/ip_gre.c	2009-05-19 01:52:34.000000000 +0200
> +++ dev-gre/net/ipv4/ip_gre.c	2009-07-01 15:30:44.000000000 +0200
> @@ -677,7 +677,7 @@
>  	}
>  
>  	tos = tiph->tos;
> -	if (tos&1) {
> +	if (tunnel->parms.o_flags&GRE_COPY_TOS || tos&1) {

This needs whitespace and parenthesis, to be safe and conform to
kernel coding style.

>  		if (skb->protocol == htons(ETH_P_IP))
>  			tos = old_iph->tos;
>  		tos &= ~1;
> @@ -804,7 +804,7 @@
>  			iph->ttl = dst_metric(&rt->u.dst, RTAX_HOPLIMIT);
>  	}
>  
> -	((__be16 *)(iph + 1))[0] = tunnel->parms.o_flags;
> +	((__be16 *)(iph + 1))[0] = tunnel->parms.o_flags&~GRE_FLAGS;
more white space

>  	((__be16 *)(iph + 1))[1] = (dev->type == ARPHRD_ETHER) ?
>  				   htons(ETH_P_TEB) : skb->protocol;
>  
> @@ -1080,7 +1080,7 @@
>  	__be16 *p = (__be16*)(iph+1);
>  
>  	memcpy(iph, &t->parms.iph, sizeof(struct iphdr));
> -	p[0]		= t->parms.o_flags;
> +	p[0]		= t->parms.o_flags&~GRE_FLAGS;
>  	p[1]		= htons(type);
>  
>  	/*
> @@ -1503,6 +1503,7 @@
>  	t->parms.iph.ttl = p.iph.ttl;
>  	t->parms.iph.tos = p.iph.tos;
>  	t->parms.iph.frag_off = p.iph.frag_off;
> +	t->parms.o_flags |= p.o_flags&GRE_COPY_TOS;
>  
>  	if (t->parms.link != p.link) {
>  		t->parms.link = p.link;
> --
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