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Question for network gurus

JACink

JACink

Mar 9, 2011
5,271
7,363
Spain
#1
I am sure there are plenty of people that know far more about networks than I do, so I would appreciate any troubleshooting ideas people may have.

I recently switched my ISP from Cable to Fiber optic, but as I already have my internal wired and wireless neworks set up, I just wanted to swap the Cable Modem for the Fiber modem.

As I don't have an option, I was given a ZTE fiber modem/router. There is only one place where I can fit this (due to cabling etc) and it is located below in my media cabinet below the TV. This is not a good place for Wifi, so I installed the fiber router there and ran a Cat6 to my other router that provides me with Wifi.

My old network (which worked fine) was set up as follows.

Cable Feed (TV+internet) > TV/Internet Divider > Cable Modem (192.168.30.2) > TP Link Router (192.168.30.1) > HP Procurve Gigabit Switch > Various Rooms and devices (including Satellite box 2)

My Router was providing Wifi to all wireless devices (on mixed a/b/g/n using channel 11 due to local traffic). All wired devices were issued with IPs betweem .10 and .50, and connected either to the router or to the HP Switch. DCHP was limited to IPs between .100 and .200.

So, my new network is like this:

Fiber optic feed > ZTE Fiber Router (192.168.30.2) > Satellite Box 1 + HP Switch + TP Link Router (192.168.30.1) > Main PC and Wireless Devices


First I turned DHCP off on the Fiber Router and left the TP Link Router assigning .100 to .200. I made the main gateway 192.168.30.2 on all devices that would let me do so. This caused some devices to connect via wifi and other would not, even two phones of the same make and model (one would, the other wouldn't). Also, Satellite Box 1, which was connected directly to the Fiber Router, would not connect with a fixed IP, however, Satellite Box 2 (same make and model) connected to the HP Switch and then to the Fiber Router worked fine with a static IP. The only way I could get Satellite Box 1 to connect was by activating DHCP on the Fiber Router.

So, I let the Fiber Router assign IPs between .50 and .99, kept the TP Link assigning .100 to .200, and made sure that all wired devices with static IPs were between .10 and .49. I also switched the Fiber Router to .1 and the TP Link to .2.

This cleared up the Wifi connectivity with the devices that wouldn't connect before, and also made Satellite Box 1 work, for a while. After a week or so, the Sat Box stopped working and the only way to get it back online was to switch from Wired to Wifi connection. Then this also stopped working a few days ago, it will no longer connect via cable or wifi.

Other erratic behaviour is various laptops and phones just seem to freeze and not load webpages although connected and with full wifi coverage. It is not an ISP problem, as my main PC (connected to the TP Link and then to the Fiber Router) shows download speads of 299MB and upload of 45MB constantly, even when other devices will not load.

I have made sure that no devices have IP confilcts and that all are addressed correctly (I did have to set the primary and secondary DNS on some of them for them to work), I have checked the routers responses during these freezes from other devices and it responds fine, no hang ups. Also, if I connect any of the devices that are refusing to respond to my mobile hotspot, they immediately respond again. This also goes for Satellite Box 1, if connected to my mobile hotspot, it works fine.

Can anyone suggest what to try next?
 
#2
Ditch the 2nd router. You're at least double-NATing which is a problem. You can go in and make sure that every setting for everything but WiFi is disabled and see if that helps, but a lot of those lower end routers will still think they are your edge. I'd suggest just ditching the 2nd router and just getting a WiFi AP and be done with it.
 
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#3
My guess is this is a DHCP-related issue. Some devices work for a while, then stop working. That suggests the device’s DHCP lease expired, then either it can’t renew its address, or it’s being assigned a bogus new gateway address or something.

Let me read your post again...

You might need to enable DHCP Helper on a router.
 
#4
Selta said:
Ditch the 2nd router. You're at least double-NATing which is a problem. You can go in and make sure that every setting for everything but WiFi is disabled and see if that helps, but a lot of those lower end routers will still think they are your edge. I'd suggest just ditching the 2nd router and just getting a WiFi AP and be done with it.
Click to expand...

Thanks for the reply.

The reason I would like to keep the 2nd router is that I need the extra (wired) ports in that location and also this Router is far superior to the crappy router they gave me. I would rather buy a Fiber modem and lose the ZTE if I need to lose one.
 
#5
Alkali Ike said:
My guess is this is a DHCP-related issue. Some devices work for a while, then stop working. That suggests the device’s DHCP lease expired, then either it can’t renew its address, or its being assigned a bogus new gateway address or something.

Let me read your post again...
Click to expand...

It could very well be something along those lines. The ZTE (Fiber) router will only allow a maximum lease of 24 hours, so maybe it has an issue readdressing, or it will not reassign the same IP again to the same device and is running out of IP's?
 
#7
I'm not sure it's a DHCP issue (it could be, or could be another issue presenting as DHCP issue). I'd again simplify it - get it down to where you have just one DHCP server, serving one DHCP scope. Whichever one you like, either the ZTE or the TP-Link should be fine. The first packet of DHCP is sent broadcast, so any DHCP server in the network can reply to it -- since you're just on one subnet, either one should work. Double NAT'ing causes all sorts of issues like this though.

WiFi device -> sends 255.255.255.255 packet DHCPDiscover -> ZTE manages to reply first -> reply can't get back due to address NAT on the TP-Link (or, perhaps some other blocking mechanism, like blocking broadcast etc)
 
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#8
Selta said:
I'm not sure it's a DHCP issue. I'd again simplify it - get it down to where you have just one DHCP server, serving one DHCP scope. Whichever one you like, either the ZTE or the TP-Link should be fine. The first packet of DHCP is sent broadcast, so any DHCP server in the network can reply to it -- since you're just on one subnet, either one should work. Double NAT'ing causes all sorts of issues like this though.
Click to expand...

Ok, so if I turn of DHCP on the TP-Link and just leave it on the ZTE, devices connected via wire or wifi to the TP-Link will still be assigned an IP via the ZTE?

I will give it a try, thanks.
 
#9
JACink said:
Ok, so if I turn of DHCP on the TP-Link and just leave it on the ZTE, devices connected via wire or wifi to the TP-Link will still be assigned an IP via the ZTE?

I will give it a try, thanks.
Click to expand...
Yes. You only need one DHCP server in a network. Even if you're assigning scopes in different subnets (i.e. 192.168.30.x/24, 192.168.29.x/24, etc), you'd just need to route between them (which isn't the case here, so I'll not muddy the waters explaining). I edited my post above about my thoughts. If you can disable most of the routing engine on the TP-Link and make it act as just a dumb switch with WiFi, we can at least see if the issue clears or continues and go from there.
 
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#12
I was going to suggest getting rid of one DHCP server.

Plug in a Windows laptop* to the LAN (or connect to wifi). Open a command prompt and enter "ipconfig /all". Does the assigned IP, subnet mask, gateway, and DNS information look correct?

Now do ipconfig /release, then ipconfig /renew, and ipconfig /all again. Does everything still look valid?

Is the DHCP server checking for duplicate addresses before assigning an IP to a device?

*Or look up the equivalent for OS X or Linux: Invalid Link Removed
 
Last edited:
#13
Well, I have turned off DHCP on the TP-Link and everything seems to work so far, I will see if I experience any glitches in the next couple of days.

However, for some reason, the ZTE router is no longer accepting credentials to log into it, it gives me user/password incorrect. This is very weird because I haven't changed the password on that router yet. I really don't want to reset that router as I didn't store the ISP settings for the Fiber (always backup!) but I gues I am going to have to :(
 
#14
Alkali Ike said:
I was going to suggest getting rid of one DHCP server.

Plug in a Windows laptop* to the LAN (or connect to wifi). Open a command prompt and enter "ipconfig /all". Does the assigned IP, subnet mask, gateway, and DNS information look correct?

Now do ipconfig /release, then ipconfig /renew, and ipconfig /all again. Does everything still look valid?

Is the DHCP server checking for duplicate addresses before assigning an IP to a device?

*Or look up the equivalent for OS X or Linux: Invalid Link Removed
Click to expand...

Yes, everything seemed fine when I ran the tests previously. I would test now, but I already deactivated DHCP so lets see if it resolves it.
 

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