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IPv6 packet headers offer many features, but extension headers may affect performance

By Donna Donnowitz
August 26, 2011
Slimmed down IPv6 packet headers were designed to assist network devices in processing IPv6 data streams faster than IPv4, however fewer fields come with a compromise, says a report from TechTarget.

A number of devices add IPv6 extension headers to packets, which can negate any potential improvements in router performance. The danger of losing these improvements is most prevalent if wide area network engineers don't have routers equipped to handle them, adds the TechTarget report.

The Internet Engineering Task Force is trying to lessen this problem by creating a standard for IPv6 extension headers.

According to a report from, an IPv6 data packet is comprised of two main parts: the header and the payload. The first 40 bytes/octets (40x8 = 320 bits) of an IPv6 packet are made up of the header data that contains the following fields: source address, destination address, version/IP version, packet priority/traffic class, flow label/QoS management, payload length, next header and time to live/hop limit.

The TechTarget report adds that, an IPv4 packet header contains 14 fields but an IPv6 packet header contains eight fields. The network router has fewer fields to deal with, but this means that not every piece of data can fit into the first 40 bytes of a standard IPv6 header. A source computer may add some extra data, such as instructions detailing how to process a particular type of information, into a separate and optional header called an IPv6 extension header.

"A router has to be able to 'think' more to handle the extension headers," Arbor Networks senior software quality assurance engineer Bill Cerveny told TechTarget. "Making a router think more potentially impacts how much [data] it can process and how many packets it can send. It can make the CPU think more than it typically has to, which can have the negative effect of overwhelming the router."

Still, not every IPv6 packet contains an extension header. In addition, considering the immaturity of IPv6 adoption, engineers are not certain about how dramatically IPv6 extension headers will affect WANs, says the report. The fact is that no one can accurately forecast the extent of the future challenges posed by extension headers.

"It's not really clear how common extension headers will be. They may be a relatively rare occurrence, but on the other hand, it's possible these extension headers will occur in large quantities," Cerveny told the news source.


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