Small change should ignore the secondary address:

Code:

awk '
    NR == FNR { seen[$1]; next }   # collect hosts from the conf file
    /}/ {                        # end of chunk, if name was in conf list, print data
        if( name in seen )
            printf( "%20s ---- %s\n", name, ip );
        name = "";
    }
    /secondary_address/ { next; }
    /host_name/ { name = $2; next; }
    /address/ { ip = $2; next; }
' host.conf chunk-file >output-file

And to answer your original question, the programme doesn't look for define host tags. Given what you posted as the contents of your file it doesn't need to. If there are other 'chunks' that need to be ignored, then it might not do the right thing depending on the contents of thoese chunks.

something like this would help if there are multiple chunks to be ignored:

Code:

awk '
    NR == FNR { seen[$1]; next }   # collect hosts from the conf file
    /define host.*{/ { snarf = 1; next; }    # ok to capture data after this point
    !snarf { next; }              # skip record if not capturing
    /}/ {                        # end of chunk, if name was in conf list, print data
        if( name in seen )
            printf( "%20s ---- %s\n", name, ip );
        name = "";
        snarf = 0;             # end of chunk turn capture off
    }
    /secondary_address/ { next; }     # ignore secondary address edit: this might need to be /_secondary_address/
    /host_name/ { name = $2; next; }  
    /address/ { ip = $2; next; }
' host.conf chunk-file >output-file

I didn't test this, so it could have a typo, but it looks clean to me.

---------- Post updated at 18:10 ---------- Previous update was at 18:02 ----------

I just reread your last posts and am a bit confused. Is the secondary address marked with secondary_address or does the string have a leading underbar? Given that your programme is looking to capture with the leading underbar, and it's not working, I'm assuming it doesn't have it in the file. The problem might also have been leading whitespace. If the configuration file records don't have any whitespace, or it's tabs and not at least a space, the leading space in your pattern (/ _secondary_address/ could be your problem too. It's hard to tell since you only posted bits and pieces of your config file.

I hope this makes some sense, and that some of it gets you going again.