I've got the following setup: A 2010 MBA and a 2013 rMBP, both running El Capitan (same issues on Yosemite though), connected to an AirPort Express 802.11n (1st Generation), which is connected via an ethernet cable to a Cisco router/modem. Airport is running in bridge mode.
10-20 times a day, internet connectivity will drop for between 10 and 90 seconds. iPads and iPhones never have issues, only the macs. The wifi connection is fine, it's just internet. Generally, only one mac loses internet connectivity, the other mac remains connected.
I'm pinging an external server, the modem and the airport continuously. During downtime, the external server is unreachable, but both the airport and the modem remain reachable.
What immediately restores the connection is clicking "Renew DHCP Lease" in the Network Preferences.
I tried to programmatically renew the DHCP lease as soon as downtime was detected (
sudo ipconfig set en1 DHCP), but that seemed to confuse the wifi connection status in the menu bar.
I'd like to solicit tips to pin down the problem in more detail, or to solve the problem entirely. (Cutting out the Airport and using the cisco router/modem directly produced similar problems).
My connection goes down every 15 minutes, like clockwork. When it's down, the DHCP entry for my laptop disappears from the list of DHCP entries in the web interface of the Cisco, even though it was not about to expire.