Zyxel Prestige 681 and 1600 SDSL Routers allow remote attackers to cause a denial of service via malformed packets with (1) an IP length less than actual packet size, or (2) fragmented packets whose size exceeds 64 kilobytes after reassembly.
https://exchange.xforce.ibmcloud.com/vulnerabilities/7704
http://www.securityfocus.com/bid/3695
http://archives.neohapsis.com/archives/bugtraq/2001-12/0190.html
http://archives.neohapsis.com/archives/bugtraq/2001-12/0140.html