Hey Ben, the only thing I can think of is that Telstra and Optus Cable networks use MAC based DHCP, they bind the IP to the MAC of the NTU or in the case of bridge mode the first client that makes a request, and often you have trouble with these things because of this, I don't really think it's a Mikrotik thing. However, as long as the Mikrotik is maintaining the same MAC on the interface plugged into the NTU and the NTU is truly in bridge mode and the Mikrotik is the only thing plugged into the NTU I can't see why it would be having issues. Is there any chance that another device might somehow be getting a DHCP request through to the NTU somehow the way you have it all plugged in ? Regards Paul -----Original Message----- From: Public [mailto:public-bounces@talk.mikrotik.com.au] On Behalf Of Ben Jackson Sent: Tuesday, 28 July 2015 10:53 AM To: MikroTik Australia Public List Subject: [MT-AU Public] Cable Modem DHCP Issues Hi All, I'm hoping someone can help me as I'm at my wit's end with this one. We use Mikrotik gear (Mainly RB2011's and and more recently, the CRS125-24G) in large residential AV situations where invariably, the Mikrotik is in dhcp client mode, in a cable internet scenario where Telstra's / Optus's modem has been placed into "bridge" mode (NAT switched off) and the carrier-supplied WAN IP address gets bound to the gateway interface of the Mikrotik. The Mikrotik, in turn is connected to, on average, about 3 UniFi access points, and at least 3-4 zones of Sonos. On initial set up, everything seems to work great, with the full bandwidth of the cable modem getting passed on to the rest of the network, even when 802.11 clients are connected (a testament to the UniFi's I my opinion - I only use dual band Pro AP's). However, after a week or so the internet connection seems to get either very slow, or stop working altogether. If I look in the logs (with dhcp logging switched on) I can see regular NAK's getting passed from the dhcp server on the cable modem. The problem is I don't really understand how DHCP works on cable modems. I'm assuming every so often the cable modem gets a new IP address from the carrier (normally after a reset) and at this point the modem is not passing this new address onto the Mikrotik which is effectively cut off from the internet. Since we are stuck with using Bigpond and Optus modems these are the only solutions I have discovered which seem to stop the issue from occurring (at least as regularly). 1) Leave the cable modem in "router" mode and switch off all extraneous services such as Wi-Fi, and also put one IP address in the dhcp pool so that the Mikrotik always gets the same private IP address. However, this creates a double nat situation which means I can no longer perform reliable port forwarding for things such as DVR's and CBus controllers (which I find the Mikrotik's great for). 2) Allow the cable modem to perform all dhcp, routing, port forwarding (which is a joke on these devices) and firewall tasks for the entire LAN and turn the CRS into an unmanaged L2 switch. The main problem here is that these Bigpond devices simply do not have the grunt to deal with large networks with lots of AV streaming and control happening. Since both of the above have severe drawbacks in terms of functionality, I wonder if anyone has had similar experiences as I am just about ready to dump the MikroTik's and start looking at other options in the hope that they play better with the Bigpond gear. Thanks in advance, Ben Jackson eLogik m:0404 924745 e: ben@elogik.net w: www.elogik.com.au [image: http://www.elogik.com.au] <http://www.elogik.com.au> _______________________________________________ Public mailing list Public@talk.mikrotik.com.au http://talk.mikrotik.com.au/mailman/listinfo/public_talk.mikrotik.com.au