Finding the Subnet Mask on AIX
This is something DB2 DBAs may need to do as a part of setting up TSAMP. Nearly every server I’ve done before has had a subnet mask of 255.255.255.0, but I ran into a server recently that wasn’t, and thought I would share how I figured out what it should be (alone, in the middle of the night, during an upgrade).
This command is probably familiar. It is used to get network adapter and IP address information on AIX:
> ifconfig -a en0: flags=1e084863,480
inet 192.0.2.236 netmask 0xfffffc00 broadcast 192.0.2.255 tcp_sendspace 262144 tcp_recvspace 262144 rfc1323 1 lo0: flags=e08084b,c0 inet 127.0.0.1 netmask 0xff000000 broadcast 127.255.255.255 inet6 ::1%1/0 tcp_sendspace 131072 tcp_recvspace 131072 rfc1323 1
The value that represents the subnet mask there is
netmask 0xfffffc00. As my Windows-oriented husband said when I discussed it with him “Why the heck is it in HEX?!?!?”. To convert that to an actual value like you would feed into db2haicu, you can use a table like this. Looking at that table, my value of 0xfffffc00 corresponds to a subnet mask of 255.255.252.0: