+static_always_inline void
+map_mss_clamping (tcp_header_t * tcp, ip_csum_t * sum, u16 mss_clamping)
+{
+ u8 *data;
+ u8 opt_len, opts_len, kind;
+ u16 mss;
+ u16 mss_value_net = clib_host_to_net_u16(mss_clamping);
+
+ if (!tcp_syn (tcp))
+ return;
+
+ opts_len = (tcp_doff (tcp) << 2) - sizeof (tcp_header_t);
+ data = (u8 *) (tcp + 1);
+ for (; opts_len > 0; opts_len -= opt_len, data += opt_len)
+ {
+ kind = data[0];
+
+ if (kind == TCP_OPTION_EOL)
+ break;
+ else if (kind == TCP_OPTION_NOOP)
+ {
+ opt_len = 1;
+ continue;
+ }
+ else
+ {
+ if (opts_len < 2)
+ return;
+ opt_len = data[1];
+
+ if (opt_len < 2 || opt_len > opts_len)
+ return;
+ }
+
+ if (kind == TCP_OPTION_MSS)
+ {
+ mss = *(u16 *) (data + 2);
+ if (clib_net_to_host_u16 (mss) > mss_clamping)
+ {
+ *sum =
+ ip_csum_update (*sum, mss, mss_value_net, ip4_header_t,
+ length);
+ clib_memcpy (data + 2, &mss_value_net, 2);
+ }
+ return;
+ }
+ }
+}
+