OIT filters IPv6 traffic on the wireless networks operated by OIT. We began doing so in November-December 2009.
We do so because the multicast traffic from devices that have IPv6 enabled degrades wireless network services provided by OIT, while at the same time being unnecessary for the network functionality OIT supports at this time.
IPv6 is the next generation of the Internet Protocol (IP). The current version of IP is IPv4; that's the version that is in widespread use throughout the Internet.
While use of IPv6 on the Internet is expected to grow in the future, at this time it is deployed in select locations on the Internet. Few sites on the Internet require clients to speak IPv6 to reach them; such Internet sites would be unreachable to the vast majority of clients, as most clients throughout the Internet have IPv4 access to the Internet, but not IPv6 access to the Internet. Most individuals using IPv6 today are doing so to experiment with the new protocol.
While IPv6 indeed may be an important future direction for the University, OIT is not prepared at this time to provide IPv6 service to the campus network. We do not route IPv6 traffic across the campus network; it does not cross OIT's IP routers. We do not provide IPv6 traffic between the campus network and the Internet. We do not assign IPv6 addresses to campus devices. And we do not provide core services over IPv6.
Although OIT does not route IPv6 traffic on the campus network, some IPv6 traffic does still appear on the campus network.
This traffic comes from some devices attached to the campus network. Some common operating systems (for example. recent versions of Mac OS X, Windows and iPhone OS) default to having both IPv4 and IPv6 enabled. When customers attach these devices to the campus network and do not disable IPv6, these devices transmit both IPv4 and IPv6 traffic. That IPv6 traffic serves little purpose; it doesn't reach the Internet, and doesn't even cross from one campus subnet to another.
OIT has for several years recommended that customers disable IPv6 on the devices they attach to the campus network, as leaving IPv6 enabled on these devices serves little purpose, and can degrade network service. Unfortunately, most customers do not do so; they leave IPv6 enabled as that's how the OS is configured by default. That's what's creating the IPv6 traffic on the campus network.
(For some devices where OIT has some control over the device's configuration (for example, Windows workstations that are members of DeSC), OIT in fact disables IPv6 on the device.)
Although this IPv6 traffic serves very little purpose on the campus network today, it can degrade network service in some circumstances.
This is because quite a lot of this IPv6 traffic is multicast traffic. Much of this traffic floods the campus IP subnet to which the sender is attached. (It does not cross the IP router to other subnets.) The traffic consumes bandwidth on the subnet. Much of it also must be examined by the other devices on that subnet that have IPv6 enabled.
The volume of this IPv6 multicast traffic is related to the number of devices on the IP subnet that have IPv6 enabled. Subnets that support many devices, particular devices on which customers have not disabled IPv6, are more likely to experience IPv6 multicast traffic rates high enough to degrade service. Other subnets are more likely to see IPv6 multicast traffic rates that are low enough that they do not degrade service.
In particular, the subnets that are associated with wireless services provided by OIT are among those experience IPv6 multicast traffic rates high enough to degrade service. To compound matters, these subnets are the same ones least able to support high rates of multicast traffic, given the performance limitations of wireless service.
Given that IPv6 is not yet supported on the campus network, and the IPv6 traffic on the wireless networks degrades network performance, OIT filters IPv6 traffic on the wireless networks provided by OIT.At this time, we are not filtering IPv6 on campus networks other that the wireless services provided by OIT. If in the future, network monitoring indicates that the IPv6 traffic on other campus subnets is high enough to degrade service on those networks, it is possible we will expand our IPv6 filtering.
OIT began filtering IPv6 in November-December 2009.
At this time, OIT filters IPv6 as it attempts to pass through each Wireless Access Point operated by OIT. These are the wireless access points that support OIT Wireless Service and Temporary Visitor Wireless Network Access (TVWNA).
This means that a wireless client of either of these services will not be able to send/receive any IPv6 traffic to/from other devices.
OIT measurements in Fall 2009 indicate that this filter reduced the overall broadcast/multicast traffic rate by 40% (measured by packet rates) on the largest campus wireless network.