1 files changed, 3 insertions, 0 deletions

diff --git a/include/uapi/linux/netfilter/nf_conntrack_tcp.h b/include/uapi/linux/netfilter/nf_conntrack_tcp.h
index 9993a421201c..ef9f80f0f529 100644
--- a/include/uapi/linux/netfilter/nf_conntrack_tcp.h
+++ b/include/uapi/linux/netfilter/nf_conntrack_tcp.h
@@ -42,6 +42,9 @@ enum tcp_conntrack {
 /* The field td_maxack has been set */
 #define IP_CT_TCP_FLAG_MAXACK_SET               0x20
 
+/* Marks possibility for expected RFC5961 challenge ACK */
+#define IP_CT_EXP_CHALLENGE_ACK                 0x40
+
 struct nf_ct_tcp_flags {
         __u8 flags;
         __u8 mask;