I haven't used chromecast for some time, possibly one or two firmware upgrades ago. I am now on Firmware Version DD-WRT v3.0-r33615M kongac (10/31/17)
Chromecast used to work, but now neither my wireless laptop nor mobile (android, Google Home app) can see the device.
On resetting the chromecast I am able to use my mobile to set it up, and that works. The chromecast connects to the router and the internet, and displays pictures on the TV. So far so good. But after that neither laptop nor mobile can see the chromecast.
I have another way of using chromecast, which is as an audio device. I use a plugin within Logitech Media Server to play music from my music server, over ethernet, which does work! So LAN to WLAN seems OK for some things. However, trying to cast from my laptop over ethernet does not work - the device is still not seen by the laptop (using the Cast feature in Chrome),
This is all on just the one router, 2.4Ghz (I don't have 5Ghz devices). The router sees the chromecast and reports its status correctly.
I can connect my mobile over wi-fi to my ethernet Desktop PC or the internet. I can use my laptop over wifi to connect to the Internet or copy files to my ethernet Desktop PC, or to play music from the music server, I don't have any obvious tool to test my mobile connecting to my laptop over wifi, so haven't tested that yet.
So it seems that what is failing is WLAN to WLAN. I don't know how the chromecast setup process works but it must be slightly different from the run-time cast process.
I have tried many things. There are suggestions about adding entries to the iptables (firewall) which made no difference. Turning on ipv6, turning off UPnP, nothing I have tried so far worked.
Can it be DNS? I use a local DNS, DNSmasq etc.
Is there any chance ddwrt will be fixed for chromecast?
It still doesn't work with version DD-WRT v3.0-r36070M, and the web admin gui is also very, very slow on my R6250.
As time has gone by I thought I'd look at the dd-wrt.com website. It now has R6250- builds. I thought I'd try the latest from there - DD-WRT v3.0-r36698M std (8/22/18).
And lo and behold, it works, sort of. The chromecast loses the connection frequently, but this seems quite common. It will do for now!
Problem SOLVED! Chromecast only support 801.11B/G only (or MIXED, if your net only has B/G nodes)
https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/7-6/...
Verified on Netgear/R6300. IGMP, Routing, Multicasting all to no avail -- as you've probably experienced, however, setting B/G only allowed multiple chromecasts as well as android-app (CastReceivers) to come online and work as they should. Please review and pass on.