[$] The trouble with IPv6 extension headers

It has taken longer than anybody might have liked, but the IPv6 protocol isslowly displacing IPv4 across the Internet. A quick, highly scientific"grep the access logs" test shows that about 16% of the traffic toLWN.net is currently using IPv6, and many large corporate networks areusing IPv6 exclusively internally. This version of the IP protocol wasdesigned to be more flexible than IPv4 in a number of ways; the "extensionheader" mechanism is one way in which that flexibility is achieved. Aproposal to formalize extension-header processing in the kernel'snetworking stack has led to some concerns, though, about how this featurewill be used and what role Linux should play in its development.