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Help needed with SBG6580 DHCP

This is a discussion on Help needed with SBG6580 DHCP within the Modems/Cable/DSL/Satellite forums, part of the Tech Support Forum category. I have a Motorola SBG6580 Cable Modem with Wifi connected to a Linksys WRT1900AC Wifi router that is used for


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Old 06-10-2017, 07:01 PM   #1
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I have a Motorola SBG6580 Cable Modem with Wifi connected to a Linksys WRT1900AC Wifi router that is used for the main internet access point. The SBG6580 (ip 192.168.0.1) is Ethernet cable connect to the WRT1900AC (ip 192.168.0.24) and the SBG6580 has DMZ and TCP port forwarding to the 192.168.0.24 address. The WRT1900AC has DDWRT firmware (192.168.1.1) and is connected to a Fedora 23/Amahi server (192.168.1.10) that handles all the DHCP serving for the linksys.

I have two issues:
1. I have registered the MAC address of the WRT1900AC with the SBG6580 and declared a set 162.168.0.24 address be served. The DHCP table now shows the address *REGISTERED INACTIVE* and from the SBG6580 I fail to be able to ping the 192.168.0.24 address even though they are connected and the green traffic light on the cable at the back of the modem is blinking. I can however SSH into the DDWRT and ping 192.168.0.1 and 192.168.1.10 (Amahi server). I can also SSH into the Amahi Server and ping 192.168.0.1 cable modem and 192.168.1.1 Linksys. Right now the SBG6580 is the only thing connected to the internet and everything connected to the Linksys is not.

2. My phone when connected to the Linksys is set static to 192.168.1.192, but when connected to the Motorola SBG6580 I have the same IP address, even though the SBG6580 DHCP should only serve up 192.168.0.2-255. Therefore, my phone has no internet through wifi since I am somehow connected to both the SBG6580 and WRT1900AC at the same time (i can log into both routers while connected to the SBG6580). I have also seen my Panasonic TV connected to the Linksys yet have a 192.168.0.xxx address like it was assigned by the SBG6580.

I am trying to figure out why can the Linksys ping the SBG6580 but not the other way around. Why can't the SBG6580 detect the Linksys MAC address and show *REGISTERED ACTIVE* in DHCP and the Linksys have internet?

And how can my phone be connected to both the SBG and Linksys at the same time? When connected to the SBG6580 why don't I have a 192.168.0.xxx address? And why would the opposite be true for my TV to be connected to the Linksys and yet show a 192.168.0.xxx address like the SBG6580 served it up?

Thank,
Brad
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Old 06-11-2017, 09:40 AM   #2
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1. you can't reserve a range in dhcp in router1 and have it to be used by router2. The x.x.0.x wan ip of the router2 is all it can use in reserved scope.

What was your train of thought for reserving the .24- range in router1?
What is the wan ip of router2?

2. if your phone is set to static ip [you don't say how so I am assuming on the phone itself] then you can't use dhcp. You will get the same ip every time since that is the one you assigned it.
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Old 06-11-2017, 06:27 PM   #3
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Thanks for responding so fast,

So, attached is my setup, or at least some of it.
1. Router 1 has a WAN IP of 192.168.0.1 so it operates on the xxx.xxx.0.xxx region and the DHCP for router 1 will hand out ip's from 192.168.0.2-255.

Router 2 has a MAC address that when seen by router 1, router 1 will assign it only to IP 192.168.0.24. That is because on router 1, TCP and UDP traffic, as well as DMZ is assigned to forward traffic to 192.168.0.24. -24 was chosen randomly by me.

Router 2 has a WAN IP of 192.168.1.1 so it operates in the xxx.xxx.1.xxx region, but since the Amahi server does the DHCP handling for router 2, router 2 has the Amahi server IP set to static on the DDWRT firmware to be 192.168.1.10 and forwards all DHCP handling to that address.

The connection that has failed is in between router 1 and router 2, but what is strange is that I can ping router 1 from router 2 and get packets. But I can't ping router 2 from router 1.

So my Plasma TV connects to router 2, the DHCP handling is handed off to the Amahi server, which recognizes the MAC address and gives an IP address to router 2 to assign to the TV and should be something like 192.168.1.xxx.
But instead it gets connected to router 2 and somehow ends up with a 192.168.0.xxx address. ***?

2. So my iPhone is set static to 192.168.1.192 in the Amahi server. So when I connect to router 2, router 2 hands off DHCP to Amahi server, the server recognizes the MAC address of the iPhone and tells router 2 the IP is static at 192.168.1.192.

However, when I connect to router 1, it should find the MAC address for the iPhone is not static for router 1, and DHCP should randomly assign the IP as something like 192.168.0.xxx. But nope, somehow on router 1 I still have 192.168.1.192, that's not even the range router 1 is supposed to assign in, ***?

Take my Windows 10 PC for example, the one I am on now. If I connect to router 2, router 2 hands off DHCP to Amahi, Amahi recognizes the MAC address as set to static 192.168.1.172, and tell router 2 to always set the IP for this PC to 192.168.1.172. No internet on router 2 though, although I can SSH into my DDWRT router 2, or Amahi server (192.168.1.10), or see the content on my attached NAS on router 2, etc.
But if I connect to router 1, as I am now, router 1 DHCP has randomly assigned my IP to 192.168.0.51, and I am on the internet , but I can't login into router 2 thru the web browser or SSH, or any of that other stuff (which as i shouldn't) , this is a good thing.

Apparently my iPhone has the same IP on both routers and I can log into both routers thru a web browser (BAD THING) but because of this I can't access the web from either.

In the long run problem 1 is way more important than problem 2, as I can always set up custom MAC address filter on both routers to block or allows the devices I want on each.

Thanks for the response.
I saw a thread from 2013 that was the same issue but with a SBG6580 and a Netgear router, and he never got a response.

Brad,
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Old 06-11-2017, 09:14 PM   #4
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"But I can't ping router 2 from router 1"
ICMP response is turned off on wan interfaces by default

"is assigned to forward traffic to 192.168.0.24"
Can't do that as .24 isn't being assigned as it appears not to be due to the "reserved inactive". I take that message to mean you didn't do a ip reservation but a ip restriction.

"No internet on router 2 though"
That I believe comes back to router2 not getting a proper wan ip address/assignment.

"instead it gets connected to router 2 and somehow ends up with a 192.168.0.xxx address. ***?"
that is strange considering the above but perhaps you turned dhcp relay in the wan interface of router2. If wanting to do nat on router2 you need to disable that feature

My suggestions are as follows:
remove the reservation on router1 for .24
change the dhcp scope on router1 to .3-254
statically assign 192.168.0.2 with gateway 192.168.0.1 to the wan interface of router2
make sure your amahi server is providing gateway 192.168.1.1
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