+/*
+ * ip4_map_ttl
+ */
+static inline void
+ip4_map_decrement_ttl (ip4_header_t *ip, u8 *error)
+{
+ i32 ttl = ip->ttl;
+
+ /* Input node should have reject packets with ttl 0. */
+ ASSERT (ip->ttl > 0);
+
+ u32 checksum = ip->checksum + clib_host_to_net_u16(0x0100);
+ checksum += checksum >= 0xffff;
+ ip->checksum = checksum;
+ ttl -= 1;
+ ip->ttl = ttl;
+ *error = ttl <= 0 ? IP4_ERROR_TIME_EXPIRED : *error;
+
+ /* Verify checksum. */
+ ASSERT (ip->checksum == ip4_header_checksum(ip));
+}
+