Description of problem:
My provider forced me to change modem to Motorola Netopia 7640-47 ADSL Modem, and DNS resolving stopped working. It seems to be a variation of the A vs. AAAA record problem, maybe it is a duplicate, but I am not sure. And I have  a feeling that the error is not completely on the modem side, however.

Version-Release number of selected component (if applicable):
Fedora 16 (testing), glibc-2.14.90-11

How reproducible: Always, firefox works only with 
network.dns.disableIPv6 set to true, other application works only with servers that have valid AAAA record. 

Additional info:
$ getent ahosts bugzilla.redhat.com

NO RESULT! running "#tcpdump -nn port 53" during this command gives 

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
22:19:48.682393 IP 192.168.1.38.39395 > 192.168.1.1.53: 57390+ A? bugzilla.redhat.com. (37)
22:19:48.682437 IP 192.168.1.38.39395 > 192.168.1.1.53: 53968+ AAAA? bugzilla.redhat.com. (37)
22:19:48.805076 IP 192.168.1.1.53 > 192.168.1.38.39395: 57390 1/0/0 A 209.132.183.69 (53)
22:19:48.807040 IP 192.168.1.1.53 > 192.168.1.38.39395: 53968- 0/0/0 (37)


Observe that the modem answers both queries: returns the A address and does not provide any AAAA address. 

========================================
for comparison the same with www.fedoraproject.org, which seems to have an ipv6 address

getent ahosts www.fedoraproject.org
213.175.193.206 STREAM wildcard.fedoraproject.org
213.175.193.206 DGRAM  
213.175.193.206 RAW    
66.35.62.166    STREAM 
66.35.62.166    DGRAM  
66.35.62.166    RAW    
85.236.55.6     STREAM 
85.236.55.6     DGRAM  
85.236.55.6     RAW    
140.211.169.197 STREAM 
140.211.169.197 DGRAM  
140.211.169.197 RAW    
152.19.134.146  STREAM 
152.19.134.146  DGRAM  
152.19.134.146  RAW    
209.132.181.16  STREAM 
209.132.181.16  DGRAM  
209.132.181.16  RAW    
2610:28:3090:3001:dead:beef:cafe:fed4 STREAM 
2610:28:3090:3001:dead:beef:cafe:fed4 DGRAM  
2610:28:3090:3001:dead:beef:cafe:fed4 RAW    

and the tcpdump looks like

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
22:22:39.217576 IP 192.168.1.38.42268 > 192.168.1.1.53: 65364+ A? www.fedoraproject.org. (39)
22:22:39.217620 IP 192.168.1.38.42268 > 192.168.1.1.53: 6945+ AAAA? www.fedoraproject.org. (39)
22:22:39.277858 IP 192.168.1.1.53 > 192.168.1.38.42268: 65364 7/0/0 CNAME wildcard.fedoraproject.org., A 213.175.193.206, A 66.35.62.166, A 85.236.55.6, A 140.211.169.197, A 152.19.134.146, A 209.132.181.16 (158)
22:22:39.424452 IP 192.168.1.1.53 > 192.168.1.38.42268: 6945 2/0/0 CNAME wildcard.fedoraproject.org., AAAA 2610:28:3090:3001:dead:beef:cafe:fed4 (90)