non routable/private ip addresses

mousers21

Hi,

I'm currently reading my ICND2 book prepping for the exam, and I was wondering about non-routable IP addresses. It's my current understanding that non-routable and private ip address ranges are the same thing. so 10.0.0.0/8, etc... are all non routable. But when I read my cisco press book by Wendell Odom, he keeps using examples when demonstrating route summarization or some other concept, where a 10.0.0.0/8 network is subnetted using VLSM or some other carving of the 10 subnet and putting a router between the various subnets.

Is this possible? Or is this just for teaching purposes. I'm confused because it seems to go against the idea of non-routable ip addreses. Then again, I can't imagine an entire 10.0.0.0/8 subnet all on a gigantic switch infrastructure. So can someone clear this up for me?

kalebksp

When people say non-routable/private they mean non-routable on the internet, they can still be routed internally.

locust76

Kaleb's right. It basically only means that if you try to send a packet to your ISP with a private source IP address, their router will just drop the packet.

You can divide the entire 10.0.0.0/8 range into /24 subnets and assign each one to a separate router interface and it will work just fine, as long as it stays "internal" and doesn't attempt to get out onto the internet using these private addresses.

For example, for my home lab, I have 192.168.1.1/24, 172.16.0.0/16 AND 10.0.0.0/8 in action with two internal routers and one router that goes to the outside, and all networks can ping each other. In addition to that, because the router that hosts the internet connection does NAT/PAT, all those private addresses can access the internet through the router using its external IP.

Ahriakin

And guys always remember it's not that they cannot be routed publicly, it's that they should not... Always egress/ingress filter RFC1918 addresses at your public edges anyway.

mousers21

Cool, thanks guys for clearing that up.

tiersten

Ahriakin wrote: »

And guys always remember it's not that they cannot be routed publicly, it's that they should not... Always egress/ingress filter RFC1918 addresses at your public edges anyway.

Bogons!

Selfmade

Read up on NAT and the functions it provides. The answers you want are in there.

wbosher

tiersten wrote: »

Bogons!

Ha, ha. Where I come from a bogon has an all together different meaning.