[SATLUG] OT(?sorta) Linksys WCG200 - DHCP wrong (or bad) address with routing and NAT turned on

Bruce Dubbs bruce.dubbs at gmail.com
Sun Mar 30 14:11:22 CDT 2008


Jennie Haywood wrote:
> On Sun, Mar 30, 2008 at 1:08 AM, ed <horned0wl93 at gmail.com> wrote:
>> Jennie Haywood wrote:
>>  > This has been incredibly frustrating.  Apparently, we had a power
>>  > outage last night.  Generally the router may go down but it comes back
>>  > up working.
>>  > Oh but not today.  {snip}
>>
>>  > SO - when the routing and NAT is turned on AND  I let it get the
>>  > address via DHCP, I get an address like 72.48.XX.XX, but I can't ping
>>  >
>>  Sounds like there's a routing issue between Grande and another cable
>>  company.  Might be happening if they're sharing equipment and/or lines.
>>  72.48.0.0-72.48.31.255 is a group of the Grande-Frisco (Grade-05)
>>  network, whereas 66.90.0.0-66.90.63.255 is a group of SmartCityOn-Line
>>  out of Florida.  Looks and sounds like you are experiencing
>>  crossed-lines somewhere up-channel from you. Perhaps one of the DHCP
>>  servers "went wild," or maybe there's been a rogue server injected into
>>  the network somewhere.
> 
> hmm.... I'm getting the 72.48.68 and the 66.90.246 networks.
> One of the things I tried was setting up the 72 address they were
> sending me with a network mask of 255.255.254.0, which is the netmask
> that they are using on the 66 network. It looks like they are using
> the last 254 number of the subnet as the default gateway so put that
> in.   That didn't work.

"the last 254 number" is not an address.  It is the netmask and 
255.255.254.0 means that the block consists of 510 addresses.  For instance:

Hosts:     66.90.246.1 to 66.90.247.254
Network:   66.90.246.0
Broadcast: 66.90.247.255

Your up address and the gateway can be any of the host addresses.  It 
just depends on how the isp has set things up.  It could be .254 or it 
could be .1.  It is arbitrary.  Once you determine the gateway address, 
you should be able to ping it.  If you can do that, any other issues are 
the isp's problem.

   -- Bruce


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