[PATCH 5/7] seg6: add End.M.GTP6.D.Di behavior

Yuya Kusakabe
2026-05-03T16:26:28Z

Add the End.M.GTP6.D.Di drop-in mode variant of End.M.GTP6.D
(RFC 9433 Section 6.4). Unlike End.M.GTP6.D, the drop-in variant
does NOT fold the GTP-U identifiers into Args.Mob.Session: the
original outer IPv6 destination is preserved at SRH[0] of the new
SRH, so the destination side can keep the original address
untouched while still benefiting from SR Policy steering.

The augmented SRH builder/destroyer is shared with End.M.GTP6.D.
The TEID and QFI parsed out of the inbound GTP-U header are
intentionally discarded for this variant (matching RFC 9433
Section 6.4).

When net.netfilter.nf_hooks_lwtunnel=1, the inner T-PDU traverses
NF_INET_PRE_ROUTING between the GTP-U strip and the SRv6 push,
mirroring End.DX4 / End.DX6.

Non-T-PDU GTP-U messages are forwarded the same way as in
End.M.GTP6.D: passed through via the lwtunnel's saved orig_input
to a downstream peer that owns the GTP-U control plane.

Configuration:

ip -6 route add 2001:db8:f::/64 \
encap seg6local action End.M.GTP6.D.Di \
srh segs 2001:db8:2::e,2001:db8:3::e \
src 2001:db8:2::1 \
dev <dev>

Link: https://www.rfc-editor.org/rfc/rfc9433.html#section-6.4
Signed-off-by: Yuya Kusakabe <yuya.kusakabe@gmail.com>
---
include/uapi/linux/seg6_local.h | 2 +
net/ipv6/seg6_local.c | 222 +++++++++++
tools/testing/selftests/net/Makefile | 1 +
.../selftests/net/srv6_end_m_gtp6_d_di_test.sh | 426 +++++++++++++++++++++
4 files changed, 651 insertions(+)

diff --git a/include/uapi/linux/seg6_local.h b/include/uapi/linux/seg6_local.h
index 7d3d3d245b47..326da65ad5aa 100644
--- a/include/uapi/linux/seg6_local.h
+++ b/include/uapi/linux/seg6_local.h
@@ -80,6 +80,8 @@ enum {
SEG6_LOCAL_ACTION_END_M_GTP6_E = 19,
/* IPv6/GTP-U decap into SRv6 (RFC 9433 Section 6.3) */
SEG6_LOCAL_ACTION_END_M_GTP6_D = 20,
+ /* IPv6/GTP-U decap into SRv6, drop-in mode (RFC 9433 Section 6.4) */
+ SEG6_LOCAL_ACTION_END_M_GTP6_D_DI = 21,

__SEG6_LOCAL_ACTION_MAX,
};
diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c
index 6ac4de529c08..cecf87cc84e5 100644
--- a/net/ipv6/seg6_local.c
+++ b/net/ipv6/seg6_local.c
@@ -2577,6 +2577,216 @@ static void seg6_end_m_gtp6_d_aug_destroy(struct seg6_local_lwt *slwt)
slwt->mobile_info.aug_srh = NULL;
}

+/* Per-skb context preserved across the NF_INET_PRE_ROUTING hook on
+ * the inner T-PDU exposed by End.M.GTP6.D.Di. Only the original
+ * outer DA is needed in the finish half (it is stamped into SRH[0]
+ * after seg6_do_srh_encap()).
+ */
+struct seg6_mobile_gtp6_d_di_cb {
+ struct in6_addr orig_dst;
+};
+
+#define SEG6_MOBILE_GTP6_D_DI_CB(skb) \
+ ((struct seg6_mobile_gtp6_d_di_cb *)((skb)->cb))
+
+static int input_action_end_m_gtp6_d_di_finish(struct net *net,
+ struct sock *sk,
+ struct sk_buff *skb)
+{
+ struct seg6_mobile_gtp6_d_di_cb cb = *SEG6_MOBILE_GTP6_D_DI_CB(skb);
+ struct dst_entry *orig_dst = skb_dst(skb);
+ enum skb_drop_reason reason;
+ const struct seg6_mobile_info *minfo;
+ struct seg6_local_lwt *slwt;
+ struct ipv6_sr_hdr *new_srh;
+ int inner_proto;
+ int err;
+
+ slwt = seg6_local_lwtunnel(orig_dst->lwtstate);
+ minfo = &slwt->mobile_info;
+
+ inner_proto = (skb->protocol == htons(ETH_P_IP)) ? IPPROTO_IPIP
+ : IPPROTO_IPV6;
+
+ err = seg6_do_srh_encap(skb, minfo->aug_srh, inner_proto);
+ if (err) {
+ reason = (err == -ENOMEM) ? SKB_DROP_REASON_SEG6_MOBILE_NOMEM
+ : SKB_DROP_REASON_SEG6_MOBILE_BAD_INNER;
+ goto drop;
+ }
+
+ skb->protocol = htons(ETH_P_IPV6);
+
+ /* Stamp the prepended segments[0] (originally zeroed in
+ * minfo->aug_srh) with the saved original outer DA, in the
+ * in-skb SRH that seg6_do_srh_encap() just pushed.
+ */
+ new_srh = (struct ipv6_sr_hdr *)(skb_network_header(skb) +
+ sizeof(struct ipv6hdr));
+ new_srh->segments[0] = cb.orig_dst;
+
+ ipv6_hdr(skb)->saddr = minfo->src_addr;
+
+ skb_set_transport_header(skb, sizeof(struct ipv6hdr));
+ nf_reset_ct(skb);
+ skb_dst_drop(skb);
+
+ seg6_lookup_any_nexthop(skb, NULL, 0, false, slwt->oif);
+ return dst_input(skb);
+
+drop:
+ kfree_skb_reason(skb, reason);
+ return -EINVAL;
+}
+
+/* RFC 9433 Section 6.4 -- End.M.GTP6.D.Di
+ * Drop-in interconnect variant of End.M.GTP6.D: instead of folding the
+ * GTP-U identifiers into Args.Mob.Session, the original outer IPv6 DA
+ * is preserved at SRH[0] so the destination side can keep the address
+ * untouched.
+ *
+ * When net.netfilter.nf_hooks_lwtunnel=1 the inner T-PDU is exposed
+ * to NF_INET_PRE_ROUTING after the GTP-U strip and before the SRv6
+ * push, identical to End.M.GTP6.D.
+ */
+static int input_action_end_m_gtp6_d_di(struct sk_buff *skb,
+ struct seg6_local_lwt *slwt)
+{
+ enum skb_drop_reason reason = SKB_DROP_REASON_SEG6_MOBILE_BAD_GTPU;
+ unsigned int outer_len, inner_off;
+ int gtp_hdrlen, inner_proto, inner_nfproto;
+ struct in6_addr orig_dst;
+ struct ipv6_sr_hdr *srh;
+ struct ipv6hdr *ip6h;
+ struct udphdr *uh;
+ u32 teid;
+ u8 inner_first, qfi;
+
+ BUILD_BUG_ON(sizeof(struct seg6_mobile_gtp6_d_di_cb) >
+ sizeof_field(struct sk_buff, cb));
+
+ srh = seg6_get_srh(skb, 0);
+ if (srh && srh->segments_left != 0) {
+ reason = SKB_DROP_REASON_SEG6_MOBILE_INVALID_SRH_SL;
+ goto drop;
+ }
+
+ if (!pskb_may_pull(skb, sizeof(struct ipv6hdr))) {
+ reason = SKB_DROP_REASON_SEG6_MOBILE_BAD_INNER;
+ goto drop;
+ }
+
+ ip6h = ipv6_hdr(skb);
+ orig_dst = ip6h->daddr;
+
+ /* Same dispatch as End.M.GTP6.D (RFC 9433 Section 6.4 reuses
+ * the S01-S11 logic from Section 6.3): GTP-U traffic is
+ * decapsulated and re-encapsulated, anything else falls
+ * through to End.
+ */
+ {
+ __be16 frag_off;
+ u8 nh = ip6h->nexthdr;
+ int upper_off;
+
+ upper_off = ipv6_skip_exthdr(skb, sizeof(*ip6h), &nh,
+ &frag_off);
+ if (upper_off < 0) {
+ /* Outer IPv6 ext-header walk failed; the GTP-U
+ * envelope below it is unreachable.
+ */
+ reason = SKB_DROP_REASON_SEG6_MOBILE_BAD_GTPU;
+ goto drop;
+ }
+
+ if (nh != IPPROTO_UDP)
+ return input_action_end(skb, slwt);
+
+ if (!pskb_may_pull(skb, upper_off + sizeof(*uh))) {
+ reason = SKB_DROP_REASON_SEG6_MOBILE_BAD_GTPU;
+ goto drop;
+ }
+
+ ip6h = ipv6_hdr(skb);
+ uh = (struct udphdr *)((u8 *)ip6h + upper_off);
+ if (uh->dest != htons(GTP1U_PORT))
+ return input_action_end(skb, slwt);
+
+ /* TEID/QFI are not consumed by the drop-in variant
+ * (RFC 9433 Section 6.4); seg6_mobile_parse_gtpu() is
+ * still required to compute the GTP-U header length so
+ * the outer chain (IPv6+UDP+GTP) can be popped correctly.
+ */
+ gtp_hdrlen = seg6_mobile_parse_gtpu(skb,
+ upper_off + sizeof(*uh),
+ &teid, &qfi);
+ if (gtp_hdrlen == -EOPNOTSUPP)
+ return seg6_mobile_passthrough_non_tpdu(skb);
+ if (gtp_hdrlen < 0) {
+ reason = SKB_DROP_REASON_SEG6_MOBILE_BAD_GTPU;
+ goto drop;
+ }
+ (void)teid;
+ (void)qfi;
+
+ outer_len = upper_off + sizeof(*uh) + gtp_hdrlen;
+ }
+
+ if (!pskb_may_pull(skb, outer_len + 1)) {
+ reason = SKB_DROP_REASON_SEG6_MOBILE_BAD_INNER;
+ goto drop;
+ }
+
+ inner_off = outer_len;
+ inner_first = *((u8 *)skb->data + inner_off);
+ switch (inner_first >> 4) {
+ case 4:
+ inner_proto = IPPROTO_IPIP;
+ inner_nfproto = NFPROTO_IPV4;
+ break;
+ case 6:
+ inner_proto = IPPROTO_IPV6;
+ inner_nfproto = NFPROTO_IPV6;
+ break;
+ default:
+ reason = SKB_DROP_REASON_SEG6_MOBILE_BAD_INNER;
+ goto drop;
+ }
+
+ if (!pskb_may_pull(skb, outer_len +
+ ((inner_proto == IPPROTO_IPIP) ?
+ sizeof(struct iphdr) : sizeof(struct ipv6hdr)))) {
+ reason = SKB_DROP_REASON_SEG6_MOBILE_BAD_INNER;
+ goto drop;
+ }
+
+ skb_pull_rcsum(skb, outer_len);
+ skb_reset_network_header(skb);
+
+ skb->protocol = (inner_proto == IPPROTO_IPIP) ? htons(ETH_P_IP)
+ : htons(ETH_P_IPV6);
+
+ skb_set_transport_header(skb,
+ (inner_proto == IPPROTO_IPIP) ?
+ sizeof(struct iphdr) :
+ sizeof(struct ipv6hdr));
+ nf_reset_ct(skb);
+
+ SEG6_MOBILE_GTP6_D_DI_CB(skb)->orig_dst = orig_dst;
+
+ if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
+ return NF_HOOK(inner_nfproto, NF_INET_PRE_ROUTING,
+ dev_net(skb->dev), NULL, skb, skb->dev,
+ NULL, input_action_end_m_gtp6_d_di_finish);
+
+ return input_action_end_m_gtp6_d_di_finish(dev_net(skb->dev), NULL,
+ skb);
+
+drop:
+ kfree_skb_reason(skb, reason);
+ return -EINVAL;
+}
+
/* RFC 9433 Section 6.5 -- End.M.GTP6.E
* Receives an SRv6 packet whose current SID is an End.M.GTP6.E SID
* (Segments Left == 1) and re-encapsulates the inner payload in
@@ -2920,6 +3130,18 @@ static struct seg6_action_desc seg6_action_table[] = {
.destroy_state = seg6_end_m_gtp6_d_aug_destroy,
},
},
+ {
+ .action = SEG6_LOCAL_ACTION_END_M_GTP6_D_DI,
+ .attrs = SEG6_F_ATTR(SEG6_LOCAL_SRH) |
+ SEG6_F_ATTR(SEG6_LOCAL_MOBILE_SRC_ADDR),
+ .optattrs = SEG6_F_LOCAL_COUNTERS |
+ SEG6_F_ATTR(SEG6_LOCAL_OIF),
+ .input = input_action_end_m_gtp6_d_di,
+ .slwt_ops = {
+ .build_state = seg6_end_m_gtp6_d_aug_build,
+ .destroy_state = seg6_end_m_gtp6_d_aug_destroy,
+ },
+ },
{
.action = SEG6_LOCAL_ACTION_END_MAP,
.attrs = SEG6_F_ATTR(SEG6_LOCAL_NH6),
diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 70cec00aebdb..ad1e2ff3842f 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -84,6 +84,7 @@ TEST_PROGS := \
sctp_vrf.sh \
skf_net_off.sh \
so_txtime.sh \
+ srv6_end_m_gtp6_d_di_test.sh \
srv6_end_m_gtp6_d_test.sh \
srv6_end_m_gtp6_e_test.sh \
srv6_end_m_gtp4_e_test.sh \
diff --git a/tools/testing/selftests/net/srv6_end_m_gtp6_d_di_test.sh b/tools/testing/selftests/net/srv6_end_m_gtp6_d_di_test.sh
new file mode 100755
index 000000000000..e2101501e866
--- /dev/null
+++ b/tools/testing/selftests/net/srv6_end_m_gtp6_d_di_test.sh
@@ -0,0 +1,426 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Selftest for the SRv6 End.M.GTP6.D.Di drop-in behavior
+# (RFC 9433 Section 6.4).
+#
+# Topology mirrors srv6_end_m_gtp6_d_test.sh. The key difference is
+# that the End.M.GTP6.D.Di action preserves the original outer IPv6
+# destination address (here 2001:db8:f::dead) as the final SRH segment,
+# rather than folding GTP-U identifiers into Args.Mob.Session.
+
+source lib.sh
+
+readonly TIMEOUT=4
+
+tcpdump_pid=""
+have_vrf=0
+
+cleanup()
+{
+ if [ -n "$tcpdump_pid" ]; then
+ kill "$tcpdump_pid" 2>/dev/null
+ wait "$tcpdump_pid" 2>/dev/null
+ fi
+ cleanup_all_ns
+}
+
+trap cleanup EXIT
+
+setup()
+{
+ setup_ns gnb srgw srupf lupf srupf_vrf
+
+ ip -n "$gnb" link set lo up
+ ip -n "$srgw" link set lo up
+ ip -n "$srupf" link set lo up
+ ip -n "$lupf" link set lo up
+ ip -n "$srupf_vrf" link set lo up
+
+ ip link add veth-n3 netns "$gnb" type veth peer name veth-n3-srgw \
+ netns "$srgw"
+ ip -n "$gnb" addr add 2001:db8:1::2/64 dev veth-n3 nodad
+ ip -n "$srgw" addr add 2001:db8:1::1/64 dev veth-n3-srgw nodad
+ ip -n "$gnb" link set veth-n3 up
+ ip -n "$srgw" link set veth-n3-srgw up
+
+ # srgw <-> srupf (SR-aware UPF, T-PDU SRv6 destination)
+ ip link add veth-n9 netns "$srgw" type veth peer name veth-n9-srupf \
+ netns "$srupf"
+ ip -n "$srgw" addr add 2001:db8:2::1/64 dev veth-n9 nodad
+ ip -n "$srupf" addr add 2001:db8:2::e/64 dev veth-n9-srupf nodad
+ ip -n "$srgw" link set veth-n9 up
+ ip -n "$srupf" link set veth-n9-srupf up
+
+ # srgw <-> lupf (legacy UPF, GTP-U control plane recipient)
+ ip link add veth-n6 netns "$srgw" type veth peer name veth-n6-lupf \
+ netns "$lupf"
+ ip -n "$srgw" addr add 2001:db8:6::1/64 dev veth-n6 nodad
+ ip -n "$lupf" addr add 2001:db8:6::e/64 dev veth-n6-lupf nodad
+ ip -n "$srgw" link set veth-n6 up
+ ip -n "$lupf" link set veth-n6-lupf up
+
+ ip netns exec "$srgw" sysctl -wq net.ipv6.conf.all.forwarding=1
+
+ local srupf_mac srgw_n9_mac lupf_mac
+ srupf_mac=$(ip -n "$srupf" -j link show veth-n9-srupf | \
+ python3 -c 'import sys, json; print(json.load(sys.stdin)[0]["address"])')
+ srgw_n9_mac=$(ip -n "$srgw" -j link show veth-n9 | \
+ python3 -c 'import sys, json; print(json.load(sys.stdin)[0]["address"])')
+ lupf_mac=$(ip -n "$lupf" -j link show veth-n6-lupf | \
+ python3 -c 'import sys, json; print(json.load(sys.stdin)[0]["address"])')
+ ip -n "$srgw" -6 neigh replace 2001:db8:2::e dev veth-n9 \
+ lladdr "$srupf_mac" nud permanent 2>/dev/null || true
+ ip -n "$srupf" -6 neigh replace 2001:db8:2::1 dev veth-n9-srupf \
+ lladdr "$srgw_n9_mac" nud permanent 2>/dev/null || true
+ # Non-T-PDU passthrough: pre-resolve the Echo Request DA so the
+ # srgw can hand the packet off to the legacy upf via veth-n6.
+ ip -n "$srgw" -6 neigh replace 2001:db8:f::dead dev veth-n6 \
+ lladdr "$lupf_mac" nud permanent 2>/dev/null || true
+
+ ip -n "$gnb" -6 route add 2001:db8:f::/64 via 2001:db8:1::1
+
+ # dev veth-n6 is the legacy UPF leg for non-T-PDU passthrough; T-PDU
+ # encap takes the IPv6 SR Policy path via a separate FIB lookup.
+ ip -n "$srgw" -6 route add 2001:db8:f::/64 \
+ encap seg6local action End.M.GTP6.D.Di \
+ srh segs 2001:db8:2::e,2001:db8:3::e \
+ src 2001:db8:2::1 \
+ dev veth-n6
+
+ ip -n "$srupf" -6 route add 2001:db8:3::/64 dev veth-n9-srupf
+
+ # Per-route VRF case: a second SR-side upf in its own VRF. The
+ # End.M.GTP6.D.Di SID for this tenant binds the SRv6 underlay output
+ # to the VRF via 'oif'. Reported as [SKIP] when CONFIG_NET_VRF is not loaded.
+ modprobe vrf 2>/dev/null
+ if ip -n "$srgw" link add vrf-n9 type vrf table 100 2>/dev/null; then
+ have_vrf=1
+ ip -n "$srgw" link set dev vrf-n9 up
+
+ ip link add veth-n9-2 netns "$srgw" type veth peer name \
+ veth-n9-2-srupf netns "$srupf_vrf"
+ ip -n "$srgw" link set dev veth-n9-2 master vrf-n9
+ ip -n "$srgw" addr add 2001:db8:4::1/64 dev veth-n9-2 nodad
+ ip -n "$srupf_vrf" addr add 2001:db8:4::e/64 dev veth-n9-2-srupf \
+ nodad
+ ip -n "$srgw" link set dev veth-n9-2 up
+ ip -n "$srupf_vrf" link set dev veth-n9-2-srupf up
+
+ local upf_vrf_mac srgw_e2_mac
+ upf_vrf_mac=$(ip -n "$srupf_vrf" -j link show \
+ veth-n9-2-srupf | python3 -c \
+ 'import sys, json; print(json.load(sys.stdin)[0]["address"])')
+ srgw_e2_mac=$(ip -n "$srgw" -j link show veth-n9-2 | \
+ python3 -c \
+ 'import sys, json; print(json.load(sys.stdin)[0]["address"])')
+ ip -n "$srgw" -6 neigh replace 2001:db8:4::e dev veth-n9-2 \
+ lladdr "$upf_vrf_mac" nud permanent 2>/dev/null || true
+ ip -n "$srupf_vrf" -6 neigh replace 2001:db8:4::1 \
+ dev veth-n9-2-srupf lladdr "$srgw_e2_mac" nud permanent \
+ 2>/dev/null || true
+
+ ip -n "$gnb" -6 route add 2001:db8:f0::/64 via 2001:db8:1::1
+
+ ip -n "$srgw" -6 route add 2001:db8:f0::/64 \
+ encap seg6local action End.M.GTP6.D.Di \
+ srh segs 2001:db8:4::e,2001:db8:5::e \
+ src 2001:db8:4::1 oif vrf-n9 \
+ dev veth-n9-2
+
+ ip -n "$srupf_vrf" -6 route add 2001:db8:5::/64 \
+ dev veth-n9-2-srupf
+ fi
+}
+
+check_dependencies()
+{
+ if ! command -v tcpdump >/dev/null; then
+ echo "SKIP: tcpdump is required"; exit "$ksft_skip"
+ fi
+ if ! command -v python3 >/dev/null; then
+ echo "SKIP: python3 is required"; exit "$ksft_skip"
+ fi
+ if ! python3 -c "import scapy.all" 2>/dev/null; then
+ echo "SKIP: python3-scapy is required"; exit "$ksft_skip"
+ fi
+
+ if ! ip route help 2>&1 | grep -qF "End.M.GTP6.D.Di"; then
+ echo "SKIP: iproute2 too old, missing seg6local action End.M.GTP6.D.Di"
+ exit "$ksft_skip"
+ fi
+}
+
+send_gtpu()
+{
+ local outer_dst="$1"
+ local srgw_mac
+
+ srgw_mac=$(ip -n "$srgw" -j link show veth-n3-srgw | \
+ python3 -c 'import sys, json; print(json.load(sys.stdin)[0]["address"])')
+
+ SRGW_MAC="$srgw_mac" OUTER_DST="$outer_dst" \
+ ip netns exec "$gnb" python3 - <<'PY'
+import os
+from scapy.all import IPv6, UDP, IP, ICMP, sendp, Ether
+mac = os.environ['SRGW_MAC']
+outer_dst = os.environ['OUTER_DST']
+gtpu = bytes.fromhex(
+ "34 ff 00 24 00 00 01 23 00 00 00 85"
+ "01 00 05 00")
+inner = bytes(IP(src='10.0.0.1', dst='10.0.0.2') / ICMP())
+pkt = (Ether(dst=mac) /
+ IPv6(src='2001:db8:1::2', dst=outer_dst) /
+ UDP(sport=2152, dport=2152) /
+ (gtpu + inner))
+sendp(pkt, iface='veth-n3', verbose=False)
+PY
+}
+
+send_gtpu_echo()
+{
+ local outer_dst="$1"
+ local srgw_mac
+
+ srgw_mac=$(ip -n "$srgw" -j link show veth-n3-srgw | \
+ python3 -c 'import sys, json; print(json.load(sys.stdin)[0]["address"])')
+
+ SRGW_MAC="$srgw_mac" OUTER_DST="$outer_dst" \
+ ip netns exec "$gnb" python3 - <<'PY'
+import os
+from scapy.all import IPv6, UDP, sendp, Ether
+mac = os.environ['SRGW_MAC']
+outer_dst = os.environ['OUTER_DST']
+gtpu_echo = bytes.fromhex("32 01 00 04 00 00 00 00 42 42 00 00")
+pkt = (Ether(dst=mac) /
+ IPv6(src='2001:db8:1::2', dst=outer_dst) /
+ UDP(sport=2152, dport=2152) /
+ gtpu_echo)
+sendp(pkt, iface='veth-n3', verbose=False)
+PY
+}
+
+run_echo_test()
+{
+ local outer_dst="$1"
+ local out
+ local rc
+
+ out=$(mktemp)
+
+ ip netns exec "$lupf" tcpdump -U -nni veth-n6-lupf -w "$out" \
+ 'udp port 2152' 2>/dev/null &
+ tcpdump_pid=$!
+ sleep 1
+
+ send_gtpu_echo "$outer_dst"
+
+ sleep 1
+ kill -INT "$tcpdump_pid" 2>/dev/null
+ wait "$tcpdump_pid" 2>/dev/null
+ tcpdump_pid=""
+
+ OUTER_DST="$outer_dst" python3 - "$out" <<'PYEOF'
+import os, sys
+from scapy.all import rdpcap, IPv6, UDP
+
+want_dst = os.environ['OUTER_DST']
+pkts = rdpcap(sys.argv[1])
+for p in pkts:
+ if IPv6 not in p or UDP not in p:
+ continue
+ if p[UDP].sport != 2152 or p[UDP].dport != 2152:
+ continue
+ if p[IPv6].dst != want_dst:
+ continue
+ payload = bytes(p[UDP].payload)
+ if len(payload) >= 2 and payload[1] == 0x01:
+ sys.exit(0)
+sys.exit("no GTPv1-U Echo Request observed at lupf "
+ "(End.M.GTP6.D.Di failed to pass non-T-PDU through)")
+PYEOF
+ rc=$?
+ rm -f "$out"
+ return $rc
+}
+
+capture_traffic()
+{
+ local capture_ns="$1"
+ local capture_iface="$2"
+ local outer_dst="$3"
+ local out="$4"
+
+ ip netns exec "$capture_ns" tcpdump -U -nni "$capture_iface" -w "$out" \
+ 'ip6' 2>/dev/null &
+ tcpdump_pid=$!
+ # Give tcpdump a brief moment to attach the BPF filter.
+ sleep 1
+
+ send_gtpu "$outer_dst"
+
+ sleep 1
+ kill -INT "$tcpdump_pid" 2>/dev/null
+ wait "$tcpdump_pid" 2>/dev/null
+ tcpdump_pid=""
+}
+
+run_test()
+{
+ local outer_dst="$1" # GTP-U outer IPv6 DA
+ local capture_ns="${2:-$srupf}" # netns where SRv6 should land
+ local capture_iface="${3:-veth-n9-srupf}"
+ local out
+
+ out=$(mktemp)
+ capture_traffic "$capture_ns" "$capture_iface" "$outer_dst" "$out"
+
+ # scapy field check: an SRv6 (RT6 type=4) packet must reach upf
+ # and one of the SRH segments must contain the original outer DA
+ # (preserved by the drop-in variant).
+ OUTER_DST="$outer_dst" python3 - "$out" <<'PYEOF'
+import os, sys
+from scapy.all import rdpcap, IPv6, IPv6ExtHdrSegmentRouting
+
+outer_dst = os.environ['OUTER_DST'].lower()
+pkts = rdpcap(sys.argv[1])
+for p in pkts:
+ if not (IPv6 in p and IPv6ExtHdrSegmentRouting in p):
+ continue
+ srh = p[IPv6ExtHdrSegmentRouting]
+ if srh.type != 4:
+ continue
+ addrs = [str(a).lower() for a in srh.addresses]
+ if outer_dst in addrs:
+ sys.exit(0)
+ sys.exit(f"original DA not in SRH segments: {addrs}")
+sys.exit("no SRv6 (RT6 type=4) packet observed")
+PYEOF
+ local rc=$?
+ rm -f "$out"
+ return $rc
+}
+
+# Verify that nf_hooks_lwtunnel=1 makes the inner T-PDU 5-tuple
+# visible to nftables on the SR Gateway. The nft rule matches on the
+# inner IPv4 source address (10.0.0.1, set by send_gtpu()); a DROP
+# verdict must prevent any SRv6 packet from reaching the upf, an
+# ACCEPT verdict must let it through unchanged.
+run_nf_test()
+{
+ local verdict="$1" # drop | accept
+ local expect_da="$2" # preserved-DA address, empty when no packet expected
+ local outer_dst="2001:db8:f::dead"
+ local out
+
+ ip netns exec "$srgw" nft flush chain ip filter prerouting
+ ip netns exec "$srgw" nft add rule ip filter prerouting \
+ ip saddr 10.0.0.1 "$verdict"
+
+ out=$(mktemp)
+ capture_traffic "$srupf" "veth-n9-srupf" "$outer_dst" "$out"
+
+ if [ -n "$expect_da" ]; then
+ OUTER_DST="$expect_da" python3 - "$out" <<'PYEOF'
+import os, sys
+from scapy.all import rdpcap, IPv6, IPv6ExtHdrSegmentRouting
+
+outer_dst = os.environ['OUTER_DST'].lower()
+pkts = rdpcap(sys.argv[1])
+for p in pkts:
+ if not (IPv6 in p and IPv6ExtHdrSegmentRouting in p):
+ continue
+ srh = p[IPv6ExtHdrSegmentRouting]
+ addrs = [str(a).lower() for a in srh.addresses]
+ if outer_dst in addrs:
+ sys.exit(0)
+sys.exit("expected SRv6 packet not observed at upf despite nft accept")
+PYEOF
+ else
+ python3 - "$out" <<'PYEOF'
+import sys
+from scapy.all import rdpcap, IPv6, IPv6ExtHdrSegmentRouting
+
+pkts = rdpcap(sys.argv[1])
+for p in pkts:
+ if IPv6 in p and IPv6ExtHdrSegmentRouting in p:
+ sys.exit("SRv6 packet leaked to upf despite nft drop on inner")
+sys.exit(0)
+PYEOF
+ fi
+ local rc=$?
+ rm -f "$out"
+ return $rc
+}
+
+main()
+{
+ local rc=0
+
+ check_dependencies
+ setup
+
+ if run_test "2001:db8:f::dead"; then
+ echo "TEST: End.M.GTP6.D.Di (default) [PASS]"
+ else
+ echo "TEST: End.M.GTP6.D.Di (default) [FAIL]"
+ rc=1
+ fi
+
+ if run_echo_test "2001:db8:f::dead"; then
+ echo "TEST: End.M.GTP6.D.Di (non-T-PDU passthrough) [PASS]"
+ else
+ echo "TEST: End.M.GTP6.D.Di (non-T-PDU passthrough) [FAIL]"
+ rc=1
+ fi
+
+ # VRF binding: SRv6 underlay output goes through vrf-n9 (table 100).
+ # Reported as [SKIP] when CONFIG_NET_VRF is not loaded.
+ if [ "$have_vrf" = "1" ]; then
+ if run_test "2001:db8:f0::dead" "$srupf_vrf" "veth-n9-2-srupf"; then
+ echo "TEST: End.M.GTP6.D.Di (oif vrf-n9) [PASS]"
+ else
+ echo "TEST: End.M.GTP6.D.Di (oif vrf-n9) [FAIL]"
+ rc=1
+ fi
+ else
+ echo "TEST: End.M.GTP6.D.Di (oif vrf-n9) [SKIP] (CONFIG_NET_VRF not loaded)"
+ fi
+
+ # Inner T-PDU netfilter hook: only meaningful when nft is present
+ # and the kernel exposes net.netfilter.nf_hooks_lwtunnel.
+ if command -v nft >/dev/null && \
+ ip netns exec "$srgw" sysctl -wq \
+ net.netfilter.nf_hooks_lwtunnel=1 2>/dev/null; then
+ ip netns exec "$srgw" nft add table ip filter
+ ip netns exec "$srgw" nft \
+ 'add chain ip filter prerouting { type filter hook prerouting priority 0; }'
+
+ if run_nf_test drop ""; then
+ echo "TEST: End.M.GTP6.D.Di (nft drop on inner) [PASS]"
+ else
+ echo "TEST: End.M.GTP6.D.Di (nft drop on inner) [FAIL]"
+ rc=1
+ fi
+
+ if run_nf_test accept "2001:db8:f::dead"; then
+ echo "TEST: End.M.GTP6.D.Di (nft accept on inner) [PASS]"
+ else
+ echo "TEST: End.M.GTP6.D.Di (nft accept on inner) [FAIL]"
+ rc=1
+ fi
+ else
+ echo "TEST: End.M.GTP6.D.Di (inner-flow netfilter hook) [SKIP]" \
+ "(nft or nf_hooks_lwtunnel unavailable)"
+ fi
+
+ if [ "$rc" -eq 0 ]; then
+ echo "TEST: End.M.GTP6.D.Di [PASS]"
+ exit "$ksft_pass"
+ else
+ echo "TEST: End.M.GTP6.D.Di [FAIL]"