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Posted by mlc on January 13, 2007, 6:17 pm
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subnetting the /24 without regards to the fact that the ISP is control
over the 64.x.x.1 address? For instance if I was to brake the /24 in to
many /30's would affect would this have? Is this not advised?
Thanks again!
mlc
Walter Roberson wrote:
> >I have been given a /24 network (64.x.x.0). I would like to be able to
> >subnet this so that I can have one network with 25 ip's (/27) and the
> >rest /30 networks. I have a cisco 7200 that is at 64.x.x.1 but I do not
> >control this. Basically it is my isp gateway. What is the best way to
> >accomplish this?
>
> If the 64.x.x.0 that you want to subnet is the same network as
> for the 64.x.x.1 on the 7200 that you do not control, then unless you
> can get some cooperation from those who control the 7200, you cannot
> subnet *at all* (at least not without adding more hardware.)
>
> No matter what kind of subnetting you want to set up, you are not
> going to be able to overcome the fact that the 7200 is set to
> 64.x.x.1 and that the 7200 is using the broadcast address 64.x.x.255 .
>
> And to get the various subnets to talk to anything other than
> within each isolated subnet, you need a router to move traffic
> between the subnets; that router is going to have to be the 7200.
>
>
> It sounds as if you have the common situation where the ISP is handing
> you a /24, and the ISP is providing the equipment, and you have been
> an IP for the router within the /24 and that the ISP has an address
> in the /24 for the router at their end of the link.
>
> In situations like that, one way is to get the ISP to do the subnetting.
>
> The approach that is taken when you want to be able to control the
> subnetting yourself, is that the ISP gives you a public /24, and
> then puts a small "carrier" subnet such as a /29 or /30 between their
> end of the link and your end of the link. The ISP then configures so
> that *all* traffic for your /24 is sent to the appropriate IP in the
> shared /30, and you configure your end so that the default gateway
> is the ISP's IP in the shared /30. ISPs encounter this kind of
> situation quite often, and if you have a /24 from them, they probably
> won't even charge you extra rental for the /30 "carrier subnet" (but
> they might charge a nominal "installation fee" to cover their employee
> time.)
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