A packet filter makes no effort to validate the contents of a data stream, so data passed over a packet filter may be bogus, invalid or otherwise incorrect. The packet filter only verifies that the network layer datagrams are correctly addressed and well-formed. Another problem with packet filtering is performance related, as having to examine each packet individually can cause lower overall performance. ****None of these are listed as disadvantages by any source online. PAcket filters are fast, low cost, flexible, and can operate up to layer 4. https://www.distributednetworks.com/internet-proxy-server/module3/packetFiltering-disadvantages.php **** http://etutorials.org/Networking/Router+firewall+security/Part+I+Security+Overview+and+Firewalls/Chapter+2.+Introduction+to+Firewalls/Firewall+Categories/ Edit: Low Performance is incorrect. All sources say packet filter only looks at header making it faster than content filtering F/W edited it to be just one answer