The network protocol layer provides the support for the IP protocol. All TCP and User Datagram Protocol (UDP) data goes through the IP layer when entering and leaving the host. TCP and UDP will use the IPv4 routing layer or the IPv6 routing layer.
The network layer also provides support for the Internet Control Message Protocol (ICMP) and ICMPv6. This is used by the IP layer to exchange information and error messages with IP layers on other hosts and routers. ICMP is used for the IPv4 protocol and ICMPv6 is used for the IPv6 protocol.