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lilly-GROUTER
Posts: 3
Registered: ‎08-24-2009
Accepted Solution

what happens if i run out of dchp?

If all 254 IP addresses (192.168.1.1) are handed out on my network, will it stop handing out IPs -or- will it start to hand out 192.168.2.1 and keep going)?
Expert
Expert
Posts: 12,649
Registered: ‎07-16-2006

Re: what happens if i run out of dchp?

The DHCP server only hands out IP addresses in the LAN subnet. If your router has LAN IP address 192.168.1.1 and subnet mask 255.255.255.0 only IP addresses 192.168.1.1-254 can be used for devices. You cannot use 192.168.2.1 because that address does not belong to the same subnet/LAN.

If the DHCP server has given out all 253 available addresses it depends on the DHCP server implementation what happens. It will probably refuse to assign an IP address until a device in the network releases an IP address and makes it available again or the lease time expires.
Mort
Posts: 3,636
Registered: ‎09-07-2006

Re: what happens if i run out of dchp?

You cannot use 192.168.2.1 because that address does not belong to the same subnet/LAN. as of your Router.
InfoSec
Posts: 1
Registered: ‎10-16-2009

Re: what happens if i run out of dchp?

The short answer is: If you have that many computers using this device simultaneously you should probably be using some beefier hardware :smileyhappy:.

The router will only allow you to use at most a class C network (256 addresses).  192.168.1.0 is generally reserved as the "network name". 192.168.1.1 is reserved for the gateway IP address.  192.168.1.255 is the broadcast address.  This leaves you you with 253 IP addresses to lease via DHCP.

I'm guessing you won't ever have 253 computers on the network simultaneously, so this shouldn't be an issue.  It is far more likely that you might have 253 different computers over a period of time.  This is where your DHCP lease time will come into play.  When a computer is leased an IP address by a DHCP server, it is leased that IP for a certain amount of time.  This is called your DHCP lease time, and can be configured in the web interface.  Hence, as computers leave the network, the leases for their IP addresses will expire.  When a lease expires, that IP address returns to the DHCP pool and can be leased to a different computer.

 

When you start running out of addresses, your subnet is said to be oversubscribed. If your DHCP lease is very high, lowering it might fix the problem (2 hours should be reasonable if you're in an environment where many people come and go). Otherwise, you'll need to redesign your network.

-- Greg

sturlalv
Posts: 1
Registered: ‎11-04-2009

Re: what happens if i run out of dchp?

I work in an open office environment and we have both a wired and a wireless network. Our servers are located off the premises and we connect through rdp. We have two printers on site who are plugged into our router (until recently an SMC device, but as this died the other day I bought a wrt160n to replace it). The printers serve both the LAN and the off-site servers and have static IP addresses (192.168.2.239 and 243, and they are for some reason set in stone...).

 

Basic setup of the wrt160n router was a breeze, and we had our WLAN up in no time. However we were uable to print, as the printers were outside the IP range given by the router. When I tried to change the gateway IP to 192.168.2.1 all the backed up print jobs printed, but the WLAN lost connectivity to the internet. I was also unable to log on to the router admin interface to reset the IP to 1.1.

 

Any good tips on how I may have the best of both worlds - both a WLAN with connectivity and be able to print?

 

 

Best regards

Sturlalv

Posts: 86
Registered: ‎11-14-2008

Re: what happens if i run out of dchp?

You could always supernet the 192.168.x networks, or you can switch to a class B network 172.16.0.0 using a subnet mask of 255.255.0.0 thus will allow for 65,000+ host addresses, but I agree that if you are using more than a class C address will support then you need at least a Cisco 670 series router. The linksys stuff at that point isnt going to cut it




Expert
Expert
Posts: 12,649
Registered: ‎07-16-2006

Re: what happens if i run out of dchp?

You cannot use subnets larger then 255.255.255.0 on a Linksys router. Linksys routers usually have a drop-down menu for the subnet mask which only allows you to select sizes up to 255.255.255.0 but not larger.

What you write is no option on a Linksys router with standard Linksys firmware.
CChristie
Posts: 1
Registered: ‎11-26-2009

Re: what happens if i run out of dchp?

Chances are that the printers were previously assigned static addresses, as in routine with such devices. Given that this is the case, all that needs to be done is to reassign the printers a static ip address in the 192.168.1.x network.
clowenstein
Posts: 1
Registered: ‎11-29-2009

Re: what happens if i run out of dchp?

Why can't you set the router to IP base address 192.168.2.1?  Then the printers at 192.168.2.239 and 243 will be in its address range.  All your local computers will pick up DHCP addresses in the 192.168.2.xxx space.   Just be sure to set the allowable DHCP addresses to exclude the addresses already in use by the printers.
Polorboy
Posts: 1
Registered: ‎11-30-2009

Re: what happens if i run out of dchp?

If you are trying to run your entire business network off of a Linksys Wireless router you should seriously rethink your network plan.  First off, your probably open to dozens of security threats to your network, especially if your using it out of the box without changing much information.  Those wireless routers are not designed to handle that kind of traffic.  There is no way to segregate traffic into vlans of any sort.  The previous person who is CCNA certifified should know this and should have said something similar.  If your company does not have an IT staff, you should also seriously consider hiring one or having an IT consulting/management firm handle your network.  These products are designed for home use, and that is where it ends.  Cisco makes an entire line of networking equipment designed for everything from small businesses to large multi-national coorporations.  I admit, I have not read this entire post but I can tell you from what I have read, your servers and printers must have a static IP address if you want them to work.  They should also be on their own subnet if possible and you should have routers forwarding traffic securly between these networks.  Your workstations should be in a subnet of their own, possibly even multiple subnets to keep network traffic segregated and keep it from going places it does not belong.  It seems like your network is in a lot more serious trouble than just worrying about running out of IP addresses.  Your DHCP should be handled by a server, having a router handle DHCP reservations is usually done as a last resort when you do not have another option.  Setting up a DHCP server is not a difficult task, especially if you already have a server runninng Microsoft Server 2003 Standard or better.  This is not intended to sound like a rant, but I read the first few posts and I could not beleive what I was seeing.  There seem to be a lot more issues here that you are not even aware of that could be a serious security threat to your entire companies network.