SB5120 issue. Guys/Gals tell me i'm not crazy in Motorola http://www.dslreports.com/forum/r22213484 en Fri, 04 Dec 2009 13:30:27 EDT Fri, 04 Dec 2009 13:30:27 EDT Re: SB5120 issue. Guys/Gals tell me i'm not crazy http://www.dslreports.com/forum/remark,22340999 NoVA_CoxUser :
said by ajwees41 See Profile :

... you need a router or a switch and pay for a second ip if your are using comast.
Not exactly ... he needs a router OR ELSE he'll need to pay Comcast for extra simultaneous IP addressses.]]> http://www.dslreports.com/forum/remark,22340999 Tue, 05 May 2009 05:29:28 EDT Re: SB5120 issue. Guys/Gals tell me i'm not crazy http://www.dslreports.com/forum/remark,22340293 ajwees41 : What do you have at home comcast or FIOS?

Like Nova said you need a router or a switch and pay for a second ip if your are using comast.]]> http://www.dslreports.com/forum/remark,22340293 Mon, 04 May 2009 23:28:45 EDT Re: SB5120 issue. Guys/Gals tell me i'm not crazy http://www.dslreports.com/forum/remark,22215145 hmurchison : NoVA_CoxUser

Thanks for the response. I was thrown a bit because I have FIOS at home but the Actiontec CPE they use does routing and Wifi so it's as close to plug and play as possible.

Looks like I'll take a trip to Fry's and pick up a small router.

The Comcast reps I spoke to were a bit green but I figured some of the blame would be on my shoulders for assuming that a DHCP server would lease more than one IP without a router in the chain.

I'll call Comcast and see if they can swap the CPE with the models they use for home networking or buy a 3rd party
Many thanks and have a great weekend. ]]> http://www.dslreports.com/forum/remark,22215145 Fri, 10 Apr 2009 11:30:31 EDT Re: SB5120 issue. Guys/Gals tell me i'm not crazy http://www.dslreports.com/forum/remark,22214188 NoVA_CoxUser : First, your ISP generally only provides you w/ a single IP.

That IP is "linked" to the MAC of the device connected to the modem

Next, everytime a new device is connected to a cable modem (technically it's everytime a device w/ a different MAC is attached), the modem needs to be power-off reset.

Lastly, while the modem indeed contains a DHCP server, it ONLY issues short-lease IPs when the modem is offline (i.e. not connected to your ISP). This allows you to access the modem's dignostics pages.

Anytime your modem is "online" the modem's DHCP server is inactive and all IPs are issued by your ISP's DHCP server.

So ... if you change the device directly attached to your modem, you'll always need to reboot the modem.

Using a router prevents this; as the router is the one device always connected to the modem -- and it never
changes -- the modem doesn't require a reboot.

If you need more than one IP (and you do since you have more than one device) you'll need a router.

It's unfortunate that your ISP's "tech support" didn't seem to understand this basic element of cable modem operation. :huh:]]> http://www.dslreports.com/forum/remark,22214188 Fri, 10 Apr 2009 06:48:30 EDT SB5120 issue. Guys/Gals tell me i'm not crazy http://www.dslreports.com/forum/remark,22213484 hmurchison : Ok i've done some searching on this and I can't get the answer I need here. Here's my issue.

Basic Windows XP PC that was direct connected to the SB5120 and works like a charm.

Brought home a Mac Cube and Netgear GigE hub. Hooked everything up and set the Mac for DHCP. No go. Tried to renew the lease several times. Finally I got it on after releasing the IP from the PC and power cycling the SB5120.

I thought my problems were over and that I'd be able to get another IP for the PC but lo and behold the PC wouldn't connect and gave me a

"An error occured while renewing interface Local Area Connection: unable to contact your DHCP Server. Request has timed out"

So in a nutshell I've found that the SB5120 is leasing a workable IP address on a "first come first served" basis and locking the other computer out with a self assigned 169.254.x.x address which of course means no interweb.

Called Comcastic twice and was told "call Apple" to which I replied "why? I can get the Mac on ..just not at the same time as the PC" and vice versa and that I could only connect the Mac with an Airport (WTF?)

So my question to those who are so gracious to let me know their suggestions and/or experiences is this. Is there something I'm being ignorant of regarding the SB5120. Am I assuming that it should automatically lease out IP addresses to my PC and Mac?

SB5120 stats

Software Version -SB5120-2.19.0.12-SCM03-NOSH
Hardware Version: 4
MIB Version: II
GUI Version: 1.0
VxWorks Version: 5.4

I noticed that the IP address varied by what I consider an interesting amount. X denotes the same number.

Mac- x.227.293.33
PC- x.231.168.83

Both IP are consistent

Any suggestion will be greatly appreciated folks. I've got a 10yr old that is getting the Mac as a surprise and I want the net to work. ]]> http://www.dslreports.com/forum/remark,22213484 Fri, 10 Apr 2009 00:04:28 EDT