diff --git a/translate.h b/translate.h
index 641768e..07db023 100644
--- a/translate.h
+++ b/translate.h
@@ -18,15 +18,40 @@
 #ifndef __TRANSLATE_H__
 #define __TRANSLATE_H__
 
-void icmp_to_icmp6(int fd, const struct iphdr *ip, const struct icmphdr *icmp, const char *payload, size_t payload_size);
-void icmp6_to_icmp(int fd, const struct ip6_hdr *ip6, const struct icmp6_hdr *icmp6, const char *payload, size_t payload_size);
+#include <linux/if_tun.h>
 
-void udp_to_udp6(int fd, const struct iphdr *ip, const struct udphdr *udp, const char *payload, size_t payload_size);
-void udp6_to_udp(int fd, const struct ip6_hdr *ip6, const struct udphdr *udp, const char *payload, size_t payload_size);
+#define MAX_TCP_HDR (15 * 4)   // Data offset field is 4 bits and counts in 32-bit words.
 
-void tcp_to_tcp6(int fd,const struct iphdr *ip, const struct tcphdr *tcp, size_t header_size,
-                 const char *payload, size_t payload_size);
-void tcp6_to_tcp(int fd,const struct ip6_hdr *ip6, const struct tcphdr *tcp, size_t header_size,
-                 const char *payload, size_t payload_size);
+// A clat_packet is an array of iovec structures representing a packet that we are translating.
+// The POS_XXX constants represent the array indices within the clat_packet that contain specific
+// parts of the packet.
+enum clat_packet_index { POS_TUNHDR, POS_IPHDR, POS_TRANSPORTHDR, POS_ICMPIPHDR,
+                         POS_PAYLOAD, POS_MAX };
+typedef struct iovec clat_packet[POS_MAX];
+
+// Returns the total length of the packet components after index.
+uint16_t payload_length(clat_packet packet, int index);
+
+// Functions to create tun, IPv4, and IPv6 headers.
+void fill_tun_header(struct tun_pi *tun_header, uint16_t proto);
+void fill_ip_header(struct iphdr *ip_targ, uint16_t payload_len, uint8_t protocol,
+                    const struct ip6_hdr *old_header);
+void fill_ip6_header(struct ip6_hdr *ip6, uint16_t payload_len, uint8_t protocol,
+                     const struct iphdr *old_header);
+
+// Translate ICMP packets.
+int icmp_to_icmp6(clat_packet out, int pos, const struct icmphdr *icmp, uint32_t checksum,
+                  const char *payload, size_t payload_size);
+int icmp6_to_icmp(clat_packet out, int pos, const struct icmp6_hdr *icmp6, uint32_t checksum,
+                  const char *payload, size_t payload_size);
+
+// Translate TCP and UDP packets.
+int tcp_packet(clat_packet out, int pos, const struct tcphdr *tcp, uint32_t checksum, size_t len);
+int udp_packet(clat_packet out, int pos, const struct udphdr *udp, uint32_t checksum, size_t len);
+
+int tcp_translate(clat_packet out, int pos, const struct tcphdr *tcp, size_t header_size,
+                  uint32_t checksum, const char *payload, size_t payload_size);
+int udp_translate(clat_packet out, int pos, const struct udphdr *udp, uint32_t checksum,
+                  const char *payload, size_t payload_size);
 
 #endif /* __TRANSLATE_H__ */