On Fri, Jun 27, 2025 at 02:45:28PM +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):
>
> 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
> }
> }
Is there a proof that this accelerates forwarding?
> Signed-off-by: Lorenzo Bianconi <[email protected]>
> ---
> net/ipv4/ipip.c | 21 +++++++++++++++++++++
> net/netfilter/nf_flow_table_ip.c | 28 ++++++++++++++++++++++++++--
> 2 files changed, 47 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..255ed53c11c927549dc87ffc6c399385e3fb68ff
> 100644
> --- a/net/netfilter/nf_flow_table_ip.c
> +++ b/net/netfilter/nf_flow_table_ip.c
> @@ -277,13 +277,31 @@ 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;
> +
> + return iph->protocol == IPPROTO_IPIP;
> +}
>
> static bool nf_flow_skb_encap_protocol(struct sk_buff *skb, __be16 proto,
> u32 *offset)
> {
> struct vlan_ethhdr *veth;
> __be16 inner_proto;
> + u16 size;
>
> switch (skb->protocol) {
> + case htons(ETH_P_IP):
> + if (nf_flow_ip4_encap_proto(skb, &size))
> + *offset += size;
This is blindly skipping the outer IP header.
> + return true;
> case htons(ETH_P_8021Q):
> if (!pskb_may_pull(skb, skb_mac_offset(skb) + sizeof(*veth)))
> return false;
> @@ -310,6 +328,7 @@ static void nf_flow_encap_pop(struct sk_buff *skb,
> struct flow_offload_tuple_rhash *tuplehash)
> {
> struct vlan_hdr *vlan_hdr;
> + u16 size;
> int i;
>
> for (i = 0; i < tuplehash->tuple.encap_num; i++) {
> @@ -331,6 +350,12 @@ static void nf_flow_encap_pop(struct sk_buff *skb,
> break;
> }
> }
> +
> + if (skb->protocol == htons(ETH_P_IP) &&
> + nf_flow_ip4_encap_proto(skb, &size)) {
> + skb_pull(skb, size);
> + skb_reset_network_header(skb);
> + }
I have a similar patch from 2023, I think I keep somewhere in my trees.
> }
>
> static unsigned int nf_flow_queue_xmit(struct net *net, struct sk_buff *skb,
> @@ -357,8 +382,7 @@ nf_flow_offload_lookup(struct nf_flowtable_ctx *ctx,
> {
> struct flow_offload_tuple tuple = {};
>
> - if (skb->protocol != htons(ETH_P_IP) &&
> - !nf_flow_skb_encap_protocol(skb, htons(ETH_P_IP), &ctx->offset))
> + if (!nf_flow_skb_encap_protocol(skb, htons(ETH_P_IP), &ctx->offset))
> return NULL;
>
> if (nf_flow_tuple_ip(ctx, skb, &tuple) < 0)
>
> --
> 2.50.0
>
