Unstable connection between router and 'cable modem'

[mirekmal]

Hello there!
I have a problem with my home network stability. It looks following

Internet
| Public IP
Cable modem/router/voice gateway (Technicolor TC7200)
| 192.168.0.1
|
| 192.168.0.2
Router (Cisco RV320)
| 192.168.52.1
|
| 192.168.52.2
Switch (Cisco SG 200-08)
|
| 192.168.52.x
All other equipment

Unfortunately TC7200 is the only choice I have as this is provided by my cable provider. This is very simple and not really good device, but it is doing basic job of delivering Internet to my house. So I decided to extend functionality by adding Cisco RV320 to my setup. TC7200 it is set to be as transparent as possible - RV320 is configured in DMZ and all firewall filtering switched off, so basically Cisco connect to Internet 'directly'.
Now, the problem is that this config is not stable. It works with full speed on my connection (I get 230~240mbps on 250mbps link... when it works), but sometimes I need to refresh pages several times to get them loaded, sometimes the same pages load instantly. I have few LAN2LAN VPN connections set to Cisco and in logs I see these being constantly dropped/reconnected. Issue seems to be related directly to link between TC7200 and RV320.
For testing purposes I replaced RV320 with my old Draytek Vigor 2920 in exactly the same configuration and with old router everything works flawlessly (beside routing between LAN and WAN being limited to ~90 mbps - but this is hardware limitation of Draytek). Also PCs connected directly to TC7200 work with full speed and network responsiveness. I also tried to put additional gigabit switch between these devices (assuming that there might be something wrong in physical layer), but this did not changes situation a bit.
I managed to limit these disruptions after some investigation on MTU. After reconfiguration of RV320 from auto to 1472 (which I found being set in my provider network) situation got a bit better, but not fully stable yet. Any advice how to proceed with further troubleshooting and what might be wrong?

 

[CaptainSTX]

It sounds to me that you could be having some problems as a result of DHCP conflicts.

Based on your description I would try the following;

Turn off DMZ on TC7200 as it should not be needed if you are correctly double NATed.
On the RV320 set a static IP in the TC7200's subnet but not in the automatic range it assigns IPs in. As you show in your original post leave the RV320's subnet as shown.
On the SG200 assign it a static IP that is in the RV320's subnet but not in the automatic range that is uses to assign IPs. Be sure that the SG200 isn't assigning DHCP.

Run your Ethernet cable from a LAN port on the TC7200 to the WAN port on the RV320. Then connect from a LAN port on the RV320 - to a LAN port or link port on the SG200. Be sure that both the cables are good and at least Cat5e.

Finally when using a VPN you may need to select different DNS servers on the RV320. Start off by trying Google at 8.8.8.8 and 8.8.4.4. If that helps use can experiment by using Namebench and see if you find something faster knowing that what ranks first today may not rank first the next time you run a test.

If this doesn't help disable the VPN and see if you can isolate it as the cause.

 

[mirekmal]

Thanks for reply, CaptainSTX! What you described is almost exactly the setup I have. All my IPs are static beside devices like mobile phones ), but IPs are assigned by RV320 DHCP server via IP to MAC binding. RV320 itself has static IP configured in TC7200 subnet manually on RV320 - DHCP on TC7200 is disabled. The difference is in DMZ - I'll test switching this off along with disabling VPNs once I get back home and will post results!

 

[CaptainSTX]

Thanks for reply, CaptainSTX! What you described is almost exactly the setup I have. All my IPs are static beside devices like mobile phones ), but IPs are assigned by RV320 DHCP server via IP to MAC binding. RV320 itself has static IP configured in TC7200 subnet manually on RV320 - DHCP on TC7200 is disabled. The difference is in DMZ - I'll test switching this off along with disabling VPNs once I get back home and will post results!

With correctly double NATed routers there is no reason that you need to shut off the DHCP server on the TC7200. As an experiment turn it back on and be sure the cable runs from a LAN port on the TC7200 to the WAN port on the RV320.

 

[mirekmal]

Resolved!

OK, got it sorted out... I hope!
So, while none suggestions worked out I took a bullet and started from scratch... The most important thing I noticed was that after restoring factory defaults to RV320 connection seemed to be stable as it should be! So step by step I made desired changes in router configuration and after every single change I performed some test to verify if that was a change that affects stability of the connection. Finally I got to one, that was causing the issue - to my surprise it was enabling SNMP agent on router! It works almost like a switch; enabling SNMP (does not matter if v1/2 or 3) immediately causes connection to become unstable and switching it off immediately restores full link stability!
I have no clue what might be relation between SNMP and link stability (initially I thought about port 161 conflict, but after careful investigation I found it not used for any other purpose. So probably it is sort of glitch in RV320 current firmware.

 

[kalzcosta]

mirekmal.


the same problem with me.

What do you do for resolve this issue ?

 

[mirekmal]

Well, finally I removed RV320 and went back to old, proven Draytek 2920... It does not allow me to fully utilize the speed of my line (I have 250mbps line, but Draytek is only capable to route 85~90mbps between LAN and WAN, but is rock stable. I'm just waiting for new firmware for RV320, maybe will help.
The most significant step to make it more stable was to disable SNMP and then I played with MTU. But I never got it fully stable for more that few hours.

 

[Antonio Valentini]

I just put a 8-Port Switch between the modem and the RV320 (WAN ) and it worked perfectly! I think it's something LAN negotiation between devices