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TOPIC: routable ip

routable ip 11 years 11 months ago #20448

What is routable ip and what is non-routable ip? How router knows whether the ip which it has to route is routable or non-routable

Re: routable ip 11 years 11 months ago #20449

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IP is a routed protocol and therefore is routable. It all depends on if Default Gateways and/or Routes are configured to forward the IP Traffic on.

Like i have been saying, its best to look through the articles as a lot of the questions you are asking are covered in them.
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Now working for a Security Company called Sec-1 Ltd in the UK, for any
Penetration Testing work visit or PM me for details.

Re: routable ip 11 years 11 months ago #20485

Are you talking about specific routes in a specific network setup...
IE.Can route to
or are you asking about completely non routeable IP... like on a local lan, or how Private IP addresses (like can't be routed to the internet...???

I understand some of it.. and some.. i'm not so clear. But I'm not sure what is being asked.


Re: routable ip 11 years 11 months ago #20488

All IP addresses are routable; as long as you have two unicast IP addresses that are on different IP networks (which is where the subnet mask comes in), then you can make a router route between them. (I carefully said 'unicast' because multicasts can be a little different but that's a digression). Having said that, there are a few IP address ranges that are not routable across the intenet - not because those addresses are some how not routable, but because by common agreement it was considered desirable to have some 'private' IP address ranges that you can use internally without fear of them being accessible to the world. If you're using your own private isolated network however you can route between these private addresses without any problem

Re: routable ip 11 years 11 months ago #20491

So in reality there is a very small number of "NON-Routable" ip addresses, which are not routeable because the IP or range is reserved? Correct?

And when we say "Non routable" we should be saying "non internet routeable"? And there is no "hard" restriction on this, just a software/protocol level decision to omit routes for them. Is that decision made on each router or is it built into the routing protocol?

IE: BGP won't let you route, specifically or by default a network?


Re: routable ip 11 years 11 months ago #20492

That's right. And the non-routable addresses are non-routable because that was the design decision taken when the internet was "invented", see RFC1818: . Exactly how the blocking is done I'm not sure - but I'm certain someone out there will shortly tell us...
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