Unidentified IP address keep popping up (10.8.11.178)

[Brons2]

ISPs rarely if ever will dole out private IPs for their clients, even using NAT.

My ISP will dole out a 192.x.x.x address if you connect a Windows machine directly to the modem. I haven't tried a Linux machine, and I don't own a Mac.

If you connect a router to the modem, it gives the router an actual IP.

Not sure how it knows, perhaps by MAC address? I assume it's the actual modem doing the NATting and not something at the central office of the ISP.

[Brons2]

They are internal addresses, not publicly routed, so generally they are LAN based therefore harmless. Yes.

One possible exception to this would be if a host on your ISP's local LAN were to become compromised. Although it would probably make the news if that happened. They'd be:

[therube]

Who is your ISP & what type of connection, satellite?

[dhouwn]

I assume it's the actual modem doing the NATting and not something at the central office of the ISP.

Is it some modem-router combination? At least there it would make somewhat sense.

[GµårÐïåñ]

They are internal addresses, not publicly routed, so generally they are LAN based therefore harmless. Yes.

One possible exception to this would be if a host on your ISP's local LAN were to become compromised. Although it would probably make the news if that happened. They'd be:

That is indeed true. If a machine on your LAN becomes compromised and you open up to it too much, then yes you can become a victim. The part about trusting your LAN is that YOU control it, so to the extent you know it and have done your due diligence, they are secure and safe to you, but otherwise, yes they can be a source of problem indeed.

[GµårÐïåñ]

ISPs rarely if ever will dole out private IPs for their clients, even using NAT.

My ISP will dole out a 192.x.x.x address if you connect a Windows machine directly to the modem. I haven't tried a Linux machine, and I don't own a Mac.

If you connect a router to the modem, it gives the router an actual IP.

Not sure how it knows, perhaps by MAC address? I assume it's the actual modem doing the NATting and not something at the central office of the ISP.

Actually your ISP is NOT giving you a 192 address. What happens is this:

1. If you have DSL, you are connecting using PPPoE and giving a username/password from which the ISP gives you a public address and the internal router and NAT allows you to use the private 192.168.0.0/16 range to manage the machines on your LAN to connect using that single IP in the router/modem to connect to the internet. The 192.168.x.x is LAN facing to YOU only, not assigned by the ISP. If you have Cable, you get the IP assigned to you directly by connecting your modem as they don't use PPPoE, instead they use dynamic assignment using MAC and also service ID of your account to verify you and give you the IP and in those cases you still have a separate router that connects to that modem which you have to use to manage your LAN. With DSL, it tends to often be a single device doing both modem and routing.
2. Internally you can access you management page at your gateway address, which is also the management IP of your router, usually 192.168.1.1 or 192.168.0.1 and sometime with like AT&T its 192.168.1.254 which is the last usable address of /24 address space. Whatever the case may be, you often have DHCP allowed, so any machine on your network that connects to the router gets an IP assigned and your gateway is the address of the router and that will in turn internally route any request from the internet to the internal IP that asked for it and vice versa. You can still have a fully functional LAN without WAN access even if the modem didn't give you a public IP.
3. Many will go with the DHCP but many also will hard assign IP addresses on their network to devices so they know who is what, allows for better management and not having to enable NetBIOS. Also will have a range of like 5 DHCP addresses in case you have a temporary device or guest coming over.

Hopefully you understand it better now. Also, although 192.168.0.0/16 is provided to the public normally, you are welcome to use the 10.0.0.0/8 as well which is also private. Its just that normally for home and small businesses the first one is sufficient and Class A 10 addresses are saved for large businesses who need millions of IP for internal networks. Take care.