Re: [PATCH nf-next v3 1/2] net: netfilter: Add IPIP flowtable SW acceleration

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Thu, Jul 03, 2025 at 04:16:02PM +0200, Lorenzo Bianconi wrote:
> Introduce SW acceleration for IPIP tunnels in the netfilter flowtable
> infrastructure.
> IPIP SW acceleration can be tested running the following scenario where
> the traffic is forwarded between two NICs (eth0 and eth1) and an IPIP
> tunnel is used to access a remote site (using eth1 as the underlay device):

Question below.

> ETH0 -- TUN0 <==> ETH1 -- [IP network] -- TUN1 (192.168.100.2)
> 
> $ip addr show
> 6: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
>     link/ether 00:00:22:33:11:55 brd ff:ff:ff:ff:ff:ff
>     inet 192.168.0.2/24 scope global eth0
>        valid_lft forever preferred_lft forever
> 7: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
>     link/ether 00:11:22:33:11:55 brd ff:ff:ff:ff:ff:ff
>     inet 192.168.1.1/24 scope global eth1
>        valid_lft forever preferred_lft forever
> 8: tun0@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1480 qdisc noqueue state UNKNOWN group default qlen 1000
>     link/ipip 192.168.1.1 peer 192.168.1.2
>     inet 192.168.100.1/24 scope global tun0
>        valid_lft forever preferred_lft forever
> 
> $ip route show
> default via 192.168.100.2 dev tun0
> 192.168.0.0/24 dev eth0 proto kernel scope link src 192.168.0.2
> 192.168.1.0/24 dev eth1 proto kernel scope link src 192.168.1.1
> 192.168.100.0/24 dev tun0 proto kernel scope link src 192.168.100.1
> 
> $nft list ruleset
> table inet filter {
>         flowtable ft {
>                 hook ingress priority filter
>                 devices = { eth0, eth1 }
>         }
> 
>         chain forward {
>                 type filter hook forward priority filter; policy accept;
>                 meta l4proto { tcp, udp } flow add @ft
>         }
> }
> 
> Reproducing the scenario described above using veths I got the following
> results:
> - TCP stream transmitted into the IPIP tunnel:
>   - net-next:				~41Gbps
>   - net-next + IPIP flowtbale support:	~40Gbps
                      ^^^^^^^^^
no gain on tx side.

> - TCP stream received from the IPIP tunnel:
>   - net-next:				~35Gbps
>   - net-next + IPIP flowtbale support:	~49Gbps
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> ---
>  net/ipv4/ipip.c                  | 21 +++++++++++++++++++++
>  net/netfilter/nf_flow_table_ip.c | 34 ++++++++++++++++++++++++++++++++--
>  2 files changed, 53 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
> index 3e03af073a1ccc3d7597a998a515b6cfdded40b5..05fb1c859170d74009d693bc8513183bdec3ff90 100644
> --- a/net/ipv4/ipip.c
> +++ b/net/ipv4/ipip.c
> @@ -353,6 +353,26 @@ ipip_tunnel_ctl(struct net_device *dev, struct ip_tunnel_parm_kern *p, int cmd)
>  	return ip_tunnel_ctl(dev, p, cmd);
>  }
>  
> +static int ipip_fill_forward_path(struct net_device_path_ctx *ctx,
> +				  struct net_device_path *path)
> +{
> +	struct ip_tunnel *tunnel = netdev_priv(ctx->dev);
> +	const struct iphdr *tiph = &tunnel->parms.iph;
> +	struct rtable *rt;
> +
> +	rt = ip_route_output(dev_net(ctx->dev), tiph->daddr, 0, 0, 0,
> +			     RT_SCOPE_UNIVERSE);
> +	if (IS_ERR(rt))
> +		return PTR_ERR(rt);
> +
> +	path->type = DEV_PATH_ETHERNET;
> +	path->dev = ctx->dev;
> +	ctx->dev = rt->dst.dev;
> +	ip_rt_put(rt);
> +
> +	return 0;
> +}
> +
>  static const struct net_device_ops ipip_netdev_ops = {
>  	.ndo_init       = ipip_tunnel_init,
>  	.ndo_uninit     = ip_tunnel_uninit,
> @@ -362,6 +382,7 @@ static const struct net_device_ops ipip_netdev_ops = {
>  	.ndo_get_stats64 = dev_get_tstats64,
>  	.ndo_get_iflink = ip_tunnel_get_iflink,
>  	.ndo_tunnel_ctl	= ipip_tunnel_ctl,
> +	.ndo_fill_forward_path = ipip_fill_forward_path,
>  };
>  
>  #define IPIP_FEATURES (NETIF_F_SG |		\
> diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c
> index 8cd4cf7ae21120f1057c4fce5aaca4e3152ae76d..6b55e00b1022f0a2b02d9bfd1bd34bb55c1b83f7 100644
> --- a/net/netfilter/nf_flow_table_ip.c
> +++ b/net/netfilter/nf_flow_table_ip.c
> @@ -277,13 +277,37 @@ static unsigned int nf_flow_xmit_xfrm(struct sk_buff *skb,
>  	return NF_STOLEN;
>  }
>  
> +static bool nf_flow_ip4_encap_proto(struct sk_buff *skb, u16 *size)
> +{
> +	struct iphdr *iph;
> +
> +	if (!pskb_may_pull(skb, sizeof(*iph)))
> +		return false;
> +
> +	iph = (struct iphdr *)skb_network_header(skb);
> +	*size = iph->ihl << 2;
> +
> +	if (ip_is_fragment(iph) || unlikely(ip_has_options(*size)))
> +		return false;
> +
> +	if (iph->ttl <= 1)
> +		return false;
> +
> +	return iph->protocol == IPPROTO_IPIP;

Once the flow is in the flowtable, it is possible to inject traffic
with forged outer IP header, this is only looking at the inner IP
header.