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New Visitor
Posts: 5
Registered: ‎05-08-2004

Subnet Mask?

How do I get my router (LINKSYS 8 port) to see what it sez is an invalid subnet mask? I'm having the same problems as many others. I can connect just fine with one computer hooked directly to modem and through router using static IP's but when attempting to connect through router after lease time is up = NO GO! Dynamic IP's don't work at all. I feel the problem is Comcast's subnet mask of 255.255.240.0 which they recently changed from the more familiar 255.255.255.0. When I input this new mask into the router it tells me that it is a invalid address, hence my questions. Anyone have the answer?
Networking Expert
Baric
Posts: 24,238
Registered: ‎07-28-2003

Re: Subnet Mask?

You can't just change your subnet without redoing your whole private address scheme. And since you can't modify the subnet Comcast is giving for the rotuer's WAN side, you must be modifying the subnet on the LAN side, which is bad news. Why would you do this? You're barking up the wrong tree. Your WAN side subnet is not something you should worry about, it's set by Comcast matches the IP and subnetting scheme they have in place in your area.

What lease is expiring and not being renewed? The WAN DHCP lease? Do you have to manually do a renew? There are others that have pointed out the BEFSR81 seems to have some sort of trouble with DHCP leases, have you checked for a firmware upgrade? What firmware are you running?
Most Valued Poster
Zathros
Posts: 1,284
Registered: ‎07-06-2003

Re: Subnet Mask?

I think you're confusing the WAN and LAN subnets.

On your router's WAN port (Comcast cable modem), you should have DHCP enabled. From Comcast, your router will then obtain a public IP address and its subnet mask. eg: 68.46.108.185, mask 255.255.240.0

On your router's LAN port (the built-in hub), you're creating your own private network, with its own private IP block and subnet mask. These private numbers have nothing to do with the public ones provided by Comcast. eg: 192.168.0.x, with a mask of 255.255.255.0

HTH,
- Dan.
- Dan.
  EARTH FIRST! We'll strip-mine the other planets later.
New Visitor
Posts: 5
Registered: ‎05-08-2004

Re: Subnet Mask?

Baric, I was hoping you would jump in on this. I'm not trying to change LAN anything, all is well there. What my issue is the 240 subnet mask. As stated before I have to use a static IP, dynamic will not connect at all, DHCP is enabled, MAC address is cloned and all works well until lease expires. After lease expires I have to jump through the hoops of resetting router and re-entering information for a static IP. I get the information from my original machine, WIN98SE using winipcfg.exe

My issue and I believe the problem to be is the WAN subnet mask. When inputting it into the router it say's it is an "invalid mask"? I think this is why it's not able to renew automatically and why dynamnic IP doesn't work period. Any suggestions?

My apologies for the anonymous name, I'm off to fix it now.
Networking Expert
Baric
Posts: 24,238
Registered: ‎07-28-2003

Re: Subnet Mask?

Navyldo said:
As stated before I have to use a static IP, dynamic will not connect at all, DHCP is enabled, MAC address is cloned and all works well until lease expires.

This makes no sense. You can't have a static IP on Comcast unless you are paying for a business account, in which case there is NO DHCP lease to worry about. So I have no idea what you're trying to say here.

If you have a static IP somehow assigned to you (how?), then your router is misconfigured, you should not be connecting with "Automatic Configuration - DHCP", but with "Static IP" instead. I don't know what you mean with "DHCP enabled", are you saing your connection type is DHCP or you are running the DHCP server in the router (which is perfectly normal)?

After lease expires I have to jump through the hoops of resetting router and re-entering information for a static IP.

This is bad news, you can't do this. You don't have a Static IP (unless you have a special account of some sort). You need to explain why you are doing this. It sounds to me like you are getting a DHCP lease, then you are taking that information and entering it as static IP information in the router (very bad move), then when the lease expires, you start having a problem (which makes perfect sense).

I get the information from my original machine, WIN98SE using winipcfg.exe

Goodness, no! That's LAN side private IP information provided by your router's DHCP server and has ABSOLUTELY nothing to do with your router's WAN side IP lease.

My issue and I believe the problem to be is the WAN subnet mask. When inputting it into the router it say's it is an "invalid mask"? I think this is why it's not able to renew automatically and why dynamnic IP doesn't work period. Any suggestions?

Yeah, don't touch the router's WAN side IP config. You need to leave it alone and let it use the values that Comcast is providing via its DHCP server.

There is nothing whatsoever wrong with a 255.255.240.0 subnet mask. If Comcast says that's what your subnet mask it, then that's what it is. Why do you think the WAN side subnet is wrong?

What you need to do is reset your router to factory defaults (see your router manual for how to do that). Once done, don't touch it except to change the admin password. The Linksys default settings are exactly what Comcast needs to work properly. That is, connection type of Automatic - DHCP (for WAN side), and DHCP server enabled for LAN side. You can mess with the LAN side settings all you want, but don't play with the WAN side or your connection will stop working.
New Visitor
Posts: 5
Registered: ‎05-08-2004

Re: Subnet Mask?

Baric, I really appreciate your effort to straighten me out but I must not be saying something right cause I've done all this

"What you need to do is reset your router to factory defaults (see your router manual for how to do that). Once done, don't touch it except to change the admin password. The Linksys default settings are exactly what Comcast needs to work properly. That is, connection type of Automatic - DHCP (for WAN side), and DHCP server enabled for LAN side. You can mess with the LAN side settings all you want, but don't play with the WAN side or your connection will stop working."

many times over. I have no issue with my LAN side everything works within my LAN (3 computers, shared printer, file sharing, PC anywhere etc. The problem lies soley with connections to Comcast servers via the router.

You were correct when you assumed that I was using

"a DHCP lease, then you are taking that information and entering it as static IP information in the router (very bad move), then when the lease expires, you start having a problem (which makes perfect sense)."

It may have been a bad move but it would work for a day!

You said to me;

"Goodness, no! That's LAN side private IP information provided by your router's DHCP server and has ABSOLUTELY nothing to do with your router's WAN side IP lease."

That would be true if I were still connected to the Router when I did it. Instead, I did this when connected directly to the cable modem. So, yes the information came from the WAN but you were correct when you thought I was using a DHCP server lease for my static IP information. I only did this to get all three computers back on line and as stated before it worked until that lease expired and I'd have to go through the process again.

Bottom line is, I'm at my wits end when configured for Automatic Connection, DHCP server enabled, MAC cloned (or not) nothing works )-: I've reset and powered down my router, computers, and modem so many times I'm thinking of building a local switch!

ps. I'm changing my name to "Frustrated in Seattle" (-:
Networking Expert
Baric
Posts: 24,238
Registered: ‎07-28-2003

Re: Subnet Mask?

OK, what you are doing, ie. getting a DHCP lease on your system while direct connected to the modem, then copying that information into the router's WAN side config is just wrong and bad. It will only work for a little while and then you're dead again.

The proper way to set it up is to connect the router and set the router to get an automatic DHCP connection to Comcast. That works, right? If not, what happens?

You connect your PC to the router and it gets a IP lease from the router. That works right? If not, what happens?

Let's be clear here, when you set things up this way (as they should be), what exactly doesn't work? The router does not renew its lease with Comcast? If so, how do you know this? Is the lease time more than 50% expired? What happens when you try to renew the lease using the router interface?

Does the PC continue to renew it's lease from the router OK?
New Visitor
Posts: 5
Registered: ‎05-08-2004

Re: Subnet Mask?

OK, what you are doing, ie. getting a DHCP lease on your system while direct connected to the modem, then copying that information into the router's WAN side config is just wrong and bad. It will only work for a little while and then you're dead again.

Yes, this is what is happening

The proper way to set it up is to connect the router and set the router to get an automatic DHCP connection to Comcast. That works, right? If not, what happens?

No, this doesn't work. After inputting the settings and re-powering everything in order modem, router, computer etc. it attempts to connect but I get nothing but "finding www.whatever.com" and then the "website cannot be found message" At this point I can ping any computer on my LAN and get a return so no problem there.

You connect your PC to the router and it gets a IP lease from the router. That works right? If not, what happens?

Yes, this works just fine from all the computers.

Let's be clear here, when you set things up this way (as they should be), what exactly doesn't work? The router does not renew its lease with Comcast? If so, how do you know this? Is the lease time more than 50% expired? What happens when you try to renew the lease using the router interface?

The only part that doesn't work is the WAN side. Remember the only time I can get a connection through the router is when I input the static IP information that I got from the DHCP server when connected directly to the modem. That connection will remain valid until the lease expires (or at least I think that is what's happening). How do you renew the lease from the router?

Does the PC continue to renew it's lease from the router OK?

Yes, this works fine.
Networking Expert
Baric
Posts: 24,238
Registered: ‎07-28-2003

Re: Subnet Mask?

What version of the BEFSR81 do you have? It's on the tag on the botton of the router.

No, this doesn't work. After inputting the settings and re-powering everything in order modem, router, computer etc. it attempts to connect but I get nothing but "finding www.whatever.com" and then the "website cannot be found message"

OK, we need to look at several things here. First I need to see the "ipconfig /all" on the system you are browsing from. Then I need to see the Status page from the router. Either copy/paste it here, or upload it to your PWP and provide us a link. Or a screen shot will do, also uploaded to your PWP. What I want to do is very exactly what your setup is, because it sounds like something is set improperly. If all settings turn out to be correct, we have to look into a router/modem issue, or perhaps a router hardware or firmware problem.

Like I said before, I have heard previous reports about the newer Linksys BEFSR81 having some kind of DHCP problem on Comcast, but it's hearsay at this point. There is nothing documented on the Linksys site and there is no updated firmware for the newer model. That's why I want the version number on your router.
New Visitor
Posts: 5
Registered: ‎05-08-2004

Re: Subnet Mask?

Baric,

I wanted to give closure to this and say thanks again for your help. I wound up buying a new router (Linksys WRT54GS) and all works just like it's supposed to. I'm still scratching my head as to what happened with my other router, maybe a lightning strike? Yes, I know, I should be surge protected....
Networking Expert
Baric
Posts: 24,238
Registered: ‎07-28-2003

Re: Subnet Mask?

Surge protector is no protection from a lightening strike, unfortunately. If a strike can jump a couple of miles from the sky to the ground, it's not going to have much trouble with a fraction of an inch between a zillion metal leads in your modem, router, computer, etc. :smileysad:

Glad you're back up and running.