PCs on network can't access certain sites

Dubh Geannain

We're recently had to replace our eircom router with a Zyxel one.

Previously I had our CCTV system enabled so that it could be accessed off site. I eventually got it working again with the replacement router; setting Firewall security to low and forwarding ports 80 and 9000 and making changes to UPnP settings.

I'm also using Dyndns and have those settings entered in the router and the DVR system. So the CCTV website can be accessed fine now, but suddenly people in the office started noticing that they can't access certain websites such as XE.com

It's a small office and IT is not my main job but these type things land on my desk. Any suggestions for what it could be? I've searched the net and can't find a solution suited to my problem yet.

I've done a tracert to xe.com as an example and rte.ie which is working.



Any suggestions?
Thanks

Mr. Fancypants

Tracert looks fine. Is it the same for everyone in the office or just one or two people? Could be the MTU size on the Zyxel router, try setting it to 1492 or lower. Have seen similar issues in the past.

Dubh Geannain

I've come across that as a possible cause but tbh I don't know how to change it.

As is, I've plugged in an older router that working for all the sites but no cameras now so I won't be able to start tricking about with it until everyone goes home (probably tomorrow).

But do you know how change it? It's not an available option from what I can see on the standard Router menus.

Edit: Sorry - Yes, it's the same for everyone in the office. About 8 PCs

Mr. Fancypants

Do you know what model Zyxel it is? I think the P-600 requires you to telnet in to change it.

Dubh Geannain

Model is: P-660HN-T1A

I found the manual for it and actually can set it via the web GUI.

Had a look there and it's set to 1492. So does that rule the MTU out as a possible cause?

Zab

You could slap on wireshark and see if you notice anything strange. Aim to have as little going on as possible to make the xe.com requests easier to find.

Mr. Fancypants

Try dropping the MTU down further. Have a look at the guide here for finding the correct MTU size for the connection :
http://www.dslreports.com/faq/695

Worth a try if nothing else.

Ctrl Alt Del

See if the issues is DNS /TCP or IP:

Check on the new router if DHCP is ok and are no silly reservations / conflicts .

On working / not working PCs check IP configuration.
Check for static or via DHCP.
Check localhosts file for some strange entries.
Check for DNS server,they might having "old" settings that not works now.
Check for IP address conflict
Check the PCs Event Viewer,apps and system for clues

Ping local by name and by IP.

Try do to a tracert based on DNS (tracert www.boards.ie) or by IP address (tracert 89.234.66.108) on PCs...

Please note that sometime,ping and tracert will return 'zero' information,as per routers configuration !

Don't think is mtu related...
Have fun

Dubh Geannain

Had a guy from eircom out today and he plugged in a new router (same model) and we got the same issues (xe.com, argos.ie etc. not loading but majority of sites do). So the problem seems to be specific to the model of router we're using.

The old router that is currently working is now plugged back in but the service guy said not to leave this one in for long and to try and resolve the issue at hand as this model was actually recalled in the past. They must have missed us when that happened :rolleyes:

I'll try the suggestions above and let ye know if I get any result.

Failing that, it's off to argos I go to buy a new router that will the job, as eircom don't provide any other models at the moment.

Ctrl Alt Del

Thanks for update !

If you are Dublin based,i can assist you ,in your office,free of charge as for a boardie' member !

Anyway,have fun !

Dubh Geannain

Ctrl Alt Del wrote: »

Thanks for update !

If you are Dublin based,i can assist you ,in your office,free of charge as for a boardie' member !

Anyway,have fun !

Cheers for the offer mate. I'm in Meath though.

I won't be able to get back to this till next week at some stage, I've other actual job related things to do first. The IT issues land on my desk because I'm the one that knows how to switch a computer off and on again

PogMoThoin

Just bridge the Zyxel modem and add a better router. The Zyxel is a terrible POS.