"Fragment Flags Invalid"

[Bind]

I installed fresh installation of solaris 10 on sparc machine with latest 
bind v9,this server is behind the hardware Firewall(policy from out to in is 
udp53&from in to out is any).
But my cisco IDS always announces this alarm from my server to other 
external clients or servers:

"Fragment Flags Invalid"
 
Src Address Dst Address Signature Name
192.168.1.1 x.x.x.x    Fragment Flags Invalid
Here is my named.conf:
options {
        version "version not currently available";
        pid-file ".../run/named.pid";
        directory ".../named/namedb";
        dump-file ".../named.dump";
        recursive-clients 10000;
        statistics-file "..../namedb/statistics";
        tcp-clients 1000;
        allow-recursion {
                any;
        };
};

logging {
        channel simple_log {
                file "/var/adm/named/bind.log" versions 3 size 50m;
                print-category yes;
                print-severity yes;
                print-time yes;
                severity warning;
        };
        category default {
                simple_log;
        };
};

key "rndc-key" {
       algorithm ,,,,,,,,,;
       secret "************";
 };

 controls {
       inet 127.0.0.1 port 953
               allow { 127.0.0.1; } keys { "rndc-key"; };
 };
does anybody have idea about this alarm? can i fix this error by tunning 
bind?
Regards
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