Here is an excerpt from AIX Certification Study Guide for AIX 5L(December 2002):
Use command smitty tcpip for basic settings – smitty will use mktcpip. Sets properties such as host name, IP address, nameserver, default gateway, subnetmask etc.
Or you can you mktcpip from the command line – like in this example:
mktcpip -h HOSTNAME -a IPaddress -m NETMASK -i IF(eg. en0) \
-n NAMESERVER -d DOMAIN -g GATEWAY -s -C 0 -A no
-s starts tcpip daemon
-C Cost of using the selected interface type
-A Active dead gateway detection: no (the default), dead gateway detection remains in passive mode.
Detail taken from HOW TO: Easily Configure TCP/IP on Your AIX System