My Linksys/Cisco E4200 v1 router flaked out every time I used iPad AirPlay Mirroring with an Apple TV, here's a fix

Posted by Paul Braren on Jun 26 2012 (updated on Nov 29 2012) in
  • Network
  • My home's internet has been quite stable and fast for many months now:

    This streak was recently disrupted by a new addition to the family's home network, an Apple TV. Unlikely to cause trouble, so I thought. But every time we used AirPlay Mirroring to push an iPad display to the TV attached to the Apple TV, the router would stop responding to ping and web administration attempts. Yes, all internet access in our home would cease.

    Hmm, seemed it could be a coincidence the first time it happened, but anything new on a network is a potential cause for concern. It was disappointing to see my router stop responding to ping, for the first time ever.

    It became very hard to believe it was merely coincidence the second time it happened. I knew I had to seek an acceptable fix quickly, with the full story found at Cisco's forum, in this somewhat related thread about AirPlay:

    Reading these 2 possible fixes:

    Applications & Gaming -> QoS ->  WMM -> ENABLE IT
    Administration -> Management -> CTF -> DISABLE IT

    I decided against messing with the WMM (Wi-Fi Multimedia) setting, since this seemed to be unlikely to address this issue, and would possibly mess with my 802.11n and/or perfected Ooma VOIP QOS settings.

    The fix:

    So instead I only turned off CTF (see screenshot below), and after an automatic router reboot, one of the few changes that requires a reboot on this router actually, things immediately worked fine. AirPlay, AirPlay Mirroring, and all our normal streaming and VOIPing activities on the home networking were humming along in perfect harmony, again. This is good, and household peace was restored.


    Here's the router's help system's description of what CTF is, I didn't notice any negative effects of disabling on my network:

    The CTF (Cut-Through Forwarding) option improves the efficiency of packet forwarding between the local network and the Internet. To use the CTF option, keep the default, Enabled.

    And here's a couple of additional footnotes:

    • not sure if disabling CTF will be needed, once I make the move to firmware 1.04 for WPS vulnerability fix
      Update: CTF off is still needed on 1.04, but I found 1.04 made Ooma unstable, so I went back  to 1.03
    • disabling CTF isn't even an option on the E4200 v2 hardware, according to comments here, so not sure what workaround those folks have
    • I do not have an understanding of how CTF and Mirroring interact, nor have I had to, given everything now "just works" again in my home

    Nov 29 2012 Update:
    Long thread, related to Cisco firmware, found here: