Systems picking up odd IP

[talksr]

Hi there,

 

I am really quite confused by what is going on this morning.

We have the following DHCP range:

10.75.44.45-10.75.47.254.

Our IP details are as follows: 10.75.44.0 255.255.252.0

Our DHCP server is our curriculum server 2012 server. The DNS distributed on a DHCP lease is the DHCP server address.

 

Of the systems I have turned on today, all of them are unable to contact the internet. They can ping the local network and domain server, but not the internet.

 

I have checked the IPs for them, and all of them seem to be showing something along the lines of 10.75.45.5, 10.75.45.6 etc. Ordinarily, they would be on 10.75.44.xyz.

Does anyone know what would be stopping them from gaining access to the internet?

 

My iPad has the IP 10.75.44.219 and it is working without problem. If I renew the lease, it just keeps picking up the same one.

 

 

Thanks in advance.

[Katy]

At an initial guess, since the netmask 255.255.252.0 would include both 10.75.44.xx and 10.75.45.xx in the same subnet, I would say that you have the subnet mask 255.255.255.0 set somewhere (possibly on the router) so that it can only access the 10.75.44.xx addresses

[talksr]

At an initial guess, since the netmask 255.255.252.0 would include both 10.75.44.xx and 10.75.45.xx in the same subnet, I would say that you have the subnet mask 255.255.255.0 set somewhere (possibly on the router) so that it can only access the 10.75.44.xx addresses

 

hmm, our router is an LGFL one so would have thought it would have been updated where appropriate. Let me check the NICs on the DHCP server.

 

 

Yes as expected, all of the NICs on the server have 255.255.255.252 configured as expected.

Edited January 31, 2017 by talksr

[Katy]

hmm, our router is an LGFL one so would have thought it would have been updated where appropriate. Let me check the NICs on the DHCP server.

 

The fact that you can access everything locally fine would rule out your local network though, I have had similar problems before and it has always been down to the managed router that I don't have access to having the wrong subnet mask set. Does a tracert from one of the affected PCs out to the Internet die at your router?

[talksr]

The fact that you can access everything locally fine would rule out your local network though, I have had similar problems before and it has always been down to the managed router that I don't have access to having the wrong subnet mask set. Does a tracert from one of the affected PCs out to the Internet die at your router?

 

I will log a call with LGFL. A tracert to google.com failes on the first hop:

1 stm-len-006.stm.internal [10.75.45.5] reports: Destination host unreachable.

Trace complete.

[Katy]

I will log a call with LGFL. A tracert to google.com failes on the first hop:

1 stm-len-006.stm.internal [10.75.45.5] reports: Destination host unreachable.

Trace complete.

 

I'm guessing the LGFL router the default gateway for your PCs? If so then yes that points at the router not being able to "see" the client, usually due to incorrect subnet mask.

[talksr]

I'm guessing the LGFL router the default gateway for your PCs? If so then yes that points at the router not being able to "see" the client, usually due to incorrect subnet mask.

 

The default GW on our PCs is the router that is correct (10.75.44.1). Just logged a call with them. Hopefully they can shed some light on it. We have an Ofsted today, so could be doing without this bother.

Edited January 31, 2017 by talksr

[talksr]

LGFL to the rescue. It was a mis-configuration at their end on their router.

 

The reason this happened today was because in the last 24 hrs, over 200 devices have connected and obtained a DHCP lease. We have a reservation of 25 for our IP phones and 25 for printers and servers so this pushed the DHCP leases into the next IP range which is why all of a sudden this issue was unearthed.

 

Just the usual Ofsted scenario, staff panicking and using and switching on everything they have in their rooms despite not using it any other time other than an Ofsted inspection. Deary me.

 

I guess it was actually helpful in one way as it identified a fault at LGFL's end. They were very quick to resolve it which was good.