Help with reverse zone for classless subnet

[Neil]

Hoping I could get some help setting up the reverse zone.  I have read
the HOW-TO, RFC2317, and DNS and Bind (3rd ed.), and I can't quite
figure it out.  Here are my various files:

named.conf
options {
 directory "/var/named";
 forwarders {206.127.0.2; 206.127.0.3; };
};
zone "." {
 type hint;
 file "named.ca";
};
zone "obi.com"{
 type master;
 file "obi.com";
};
zone "0.0.127.in-addr.arpa"{
 type master;
 file "named.local";
};
zone "17.99.209.in-addr.arpa"{
 type master;
 file "17.99.209";
};

obi.com
; The full zone file
;
@               IN      SOA     talus.obi.com.  root.obi.com. (
                        1999092401 ; serial
                        8H ; refresh
                        2H ; retry
                        1W ; expire
                        1D ; default_ttl
                        )
;
@               IN      TXT     "OsteoBiologics, Inc."

localhost       IN      A       127.0.0.1

gw              IN      A       209.99.17.129
gw              IN      HINFO   "Pipeline 75" "SCM"
gw              IN      TXT     "The router"

talus           IN      A       209.99.17.189
talus           IN      MX      20      ns.obi.com.
talus           IN      HINFO   "Pentium" "Linux Mandrake-6.0"

ns              IN      A       209.99.17.135
ns              IN      MX      20      ns.obi.com.
ns              IN      HINFO   "PowerMac" "MacOS 8.1"

www             IN      CNAME   ns.obi.com.

ulna            IN      A       209.99.17.152
ulna            IN      HINFO   "Pentium" "RedHat Linux 5.2"

@               IN      MX      10      ns.obi.com.
@               IN      NS      talus

and finally, 17.99.209
$TTL 1D

@ IN SOA talus.obi.com. root.obi.com.  (
1999092401 ; Serial
8H ; Refresh
2H ; Retry
1W ; Expire
1D); Minimum

IN NS talus.obi.com.

129 IN PTR gw.obi.com.
135 IN PTR ns.obi.com.
189 IN PTR talus.obi.com.

While this works, it claims authority for the whole 209.99.17.xxx group,
while I really only have authority over 209.99.17/26.  I have tried
setting up the zone file 128.17.99.209 and using PTR records, but this
didn't work.  I think I'm missing something.

Thanks in advance for the help!

Neil Leatherbury