Maximum Number of TCP/IP Host Table Entries

Resolving The Problem

/QIBM/USERDATA/OS400/TCPIP/QTOCHOSTS contains the local host table entries.

( QUSRSYS/QATOCHOST is the old file still used for compatibility after V6R1. )

In theory, there could be over 4G of records (Internet addresses and associated host names) in the file according to the Database file sizes topic in the Information Center. However, not all the supporting code is able to handle that much data (for example, the UIM code used to display the table information for CFGTCP, Option 10). There is a 32K limit on table entries in UIM. This means that there could be 32000 host names (8000 - 32000 ip addresses). The host table was never designed to be used for so many hosts however and there could be significant performance issues once a large number of entries is in the local host table. DNS is designed for this and the recommendation is to have as many entries as possible in a DNS server and then have the iseries point to that DNS server after reviewing the local host table.