I may reveal some ignorance with this question, but I am really confused. We have 3 static IPs and one gateway/modem with my organization. The gateway/modem is located in a remote area of our building, so we only have one line from the gateway/modem to our "IT Office" where our routers, switches, servers, etc. are located.

I created two VLANS on our primary switch. All of the router WAN ports and the line from the gateway/modem are on one VLAN (public data); all internal LAN traffic is on the other (private data). The "public" VLAN has 3 different public IPs with one gateway IP coming from the gateway/modem.

Here is the problem: the routers will suddenly lose the connection with the modem, and our internet traffic will crash. And then it will come back up a minute later and work for 2-3 minutes before dying again. Sometimes one of the routers will continue to work fine. If I disconnect the gateway/modem line from the switch and connect it directly to one WAN port on one router, everything works fine (at least through that one public IP).

Is there something I am missing that would make this a likely scenario for disaster? Does this look like a possible hardware issue? I think either the switch is causing the problem or I am missing something obvious.


  • Example IP addresses that are similar to what you've done would help make this easier to figure out. If that checks out, we might need router config, too. Any interesting logs on your router or switch? – scottm32768 Mar 19 '13 at 20:09
  • Sure. One VLAN (20 ports) has all 192.168.2.x traffic; the other VLAN (4 ports) has 50.x.x.225-229 traffic. The gateway address is 50.x.x.230. The gateway is plugged into port 24, and the public WANs from the routers are plugged into ports 21, 22 & 23. I'm going to take a look at some logs and maybe even mirror the traffic on the four ports for VLAN 2. – professornayr Mar 19 '13 at 20:30
  • I'm starting to think it is an issue with the VLAN on my switch. I put all of the Public traffic into a completely separate switch, and so far, everything is working fine. I'll post back in a few days after I've had more time to make sure the connection is working fine. – professornayr Mar 21 '13 at 18:27

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