Internet servers are not supposed to route private IP ranges such as 192.168.x.x.
How do they achieve this? Should an administrator enable a specific firewall rule on the router or is it coded in the hardware/firmware/kernel of the router?
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Most ISPs will have hardcoded ACLs to prevent routing of private traffic. In the event they do not, the lack of a locatable return address will prevent these packets from going anywhere regardless. BGP (Border Gateway Protocol), the core routing protocol of the internet, only advertises public routes. It is common to find an ACL similar to the following on internet-facing Cisco routers: This will block private addresses, including APIPA and loopback addresses from traversing a router interface after applied via an access-group. The firmware on some SOHO routers has this functionality built-in. |
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You need to have a better understanding of how the internet and routing works. Private IP Address ranges are simply not available for other companies to use. They are registered by an RIR. This is the Whois record for 192.168.0.1: If any internet provider attempted to use it in their (public facing/internet connected) infrastructure, and they configured routes on a router accordingly, there would be nothing stopping them using it internally. However, if they start giving out these IPs to their subscribers via DHCP/static, and their customers also use these addresses internally, it could lead to some very interesting problems on the client side. Also, internet providers connect to each other through a variety of methods. Unless every other ISP was to also add routes, it simply will not be reachable. This is without getting in to BGP or anything more complicated... ... To try and make it a bit simpler... Put it this way, any ISP can use any IP block they like, but, in order for the internet to work, they need to configure the way each route to each other. The private IP ranges are just reserved/registered by the authority that dishes out other IP blocks. In the same way, I can easily use public IP address ranges on my internal network, but, outside/external people will not be able to route to my network without adding their own custom routes. ** I have tried rewriting this a few times, it is quite a complex situation and hard to explain... If you have any other follow up questions, feel free to ask. ** |
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If any internet provider attempted to use it in their (public facing/internet connected) infrastructure, and they configured routes on a router accordingly, there would be nothing stopping them using it internally. |
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protected by Community♦ Feb 23 '12 at 4:48
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