First you need to catalog the remote instance.
db2 catalog tcpip node <my alias node name> remote <host or host alias name> server <port>
db2 terminate to make sure the catalog entry remains.
Now you can actually catalog the remote database.
db2 catalog db <remote database name> as <local alias> at node <node alias supplied above>
And once again issue
Here is an example of what this could look like:
db2 catalog tcpip node devinst1 remote devservera server 50100;
db2 catalog db crmdb as remotedb at node devinst1;
Now you can connect to that local database using either the db name (crmdb) or the alias name (remotedb) depending on your needs.
Note: Sometimes you can run into issues where it will say things about a null package id. This would mean that particular packages need to be bound for the connection to work. Easiest way to solve this is to have your instance owner id (of the remote database) make the first connection and then disconnect or to have your id you are using have
BINDADD authority. Then the correct packages will get bound. You may not run into this, especially if you are on the same version and fix pack level of DB. If you ever differ between "client" and "server" is when you for sure have to do this.