AirPort interface down/up bug on Mac OS X (version 10.6.6)

This page reports a bug on Mac OS X (version 10.6.6) about AirPort interface down and then up when session timeout for authentication (RADIUS attribute 27) is configured in the wireless access point.

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Reporting AirPort interface down/up bug on Mac OS X (version 10.6.6)

Date: Mar. 1, 2011
Author: Hirochika Asai

Summary of this issue

AirPort interface on MacBook Pro with certain Broadcom hardwares/firmwares would go down when the session timeout for authentication (RADIUS attribute 27) that is configured in wireless access points has reached. The interface would go up soon after this interface down. This bug causes some problems. A main problem is that packets cannot be sent for some seconds. Another problem is that IP addresses assigned by auto-configuration mechanisms (e.g., DHCP and IPv6 router advertisement) are deleted when the interface goes down. This causes the same problem reported in the article [IPv6 router advertisement processing bug on Mac OS X]. Moreover, this address deletion also occurs in IPv4 addresses configured by DHCP. Therefore, this bug is quite serious.

Specific firmware affected

We investigated the causes of this issue by testing one MacBook Pro.

Detailed description on this issue

AirPort interface down/up when session timeout reaches

We confirmed this bug with Cisco Wireless LAN Controller 5508 (WLC5508). Note that this bug does not appear on other OSes such as Microsoft Windows 7 with the same wireless access points and the same configuration. We configured 1800 seconds for Session-Timeout on WLC5508 as shown in Fig. 1.

Session-Timeout (RADIUS attribute 27) configuration in WLC5508

When the session timeout reaches, the interface status became down and the addresses assigned by auto-configuration mechanisms had removed. At the same time as this problem, we found the following messages in /var/log/kernel.log. 

Jan  4 18:04:58 dhcp-xxx kernel[0]: Auth result for: xx:xx:xx:xx:xx:xx MAC AUTH succeeded
Jan  4 18:04:58 dhcp-xxx kernel[0]: AirPort: RSN handshake complete on en1
Jan  4 18:35:14 dhcp-xxx kernel[0]: Auth result for: xx:xx:xx:xx:xx:xx MAC AUTH succeeded
Jan  4 18:35:14 dhcp-xxx kernel[0]: AirPort: RSN handshake complete on en1

Here, xx:xx:xx:xx:xx:xx is a MAC address of the associating access point.

We could not confirm whether these messages are ordinal ones or not but the timestams of these messages match the interface down/up.

Regression

The best solution to avoid this issue is not to use session timeout for authentication (RADIUS attribute 27). However, you may not have the permission to configure access points to which you would connect. Avoiding using auto-configuration mechanisms, such as DHCP and IPv6 address autoconfiguration with router advertisements, can regress this issue. However, the interface goes down even though you avoid using them, and some packets would be lost. If you use the auto-configuration mechanisms, IPv6 temporary address should not be used to regress this issue as described in the article [IPv6 router advertisement processing bug on Mac OS X].

Conclusion

In this article, we reported a bug on Mac OS X (version 10.6.6) about AirPort interface down/up when the session timeout reaches. Since this bug is quite serious that causes packet loss and other problems especially with IPv6 temporary address configuration. We might regress this bug by configuration of wirelss access points but we should have troubles in case we are not administrators of some access points. Hence, we have already reported this bug to Apple's bug report site. Hopefully, this issue would be resolved soon by software updates.