On Thursday 05 October 2006 14:44, Hans-Werner Hilse <[EMAIL PROTECTED]> wrote about 'Re: [gentoo-user] OT - ipkungfu not': > Concerning the IPs you've mentioned, that looks like > 70.234.122.249 = 01000110.11101010.01111010.11111001 > 70.234.122.250 = 01000110.11101010.01111010.11111010 > 70.234.122.251 = 01000110.11101010.01111010.11111011 > > Note that the first 29 bits are all equal.
In addition, the first 30 bits are all equal. > So it would be sufficient to > specify a /29 netmask (255.255.255.248). However, we can't specify a /30 because two addresses in each block (the highest and the lowest) are reserved for "network" (anycast) and "broadcast" (multicast). You don't have to know what these are used for, just that you can't assign them. Since one of your addresses is all 1's after the common part (IPv4 addres is 32 bits, common part is 30 bits, so that means the 2 bits at the end are both 1), you have to move up to a larger netmask (in this case the next largest, /29, will do). > Note that this will also > include the IP 70.234.122.248. As would a /30, but in both cases it will be reserved (for "network") and can't be assigned to a single machine. In a /30 your 70.234.122.251 would be reserved (for "broadcast") which is why you need to use /29. > It would probably not be wise to > actually set this as an IP netmask when configuring the interfaces > (will most certainly break routing and broadcasts), ??? SBC assigns our household a /29 block. It is *required* that we configure that as our 255.255.255.248 as our netmask if we want routing to work. I've also used /30 and /28 networks for routing. Classful addressing is dead, long live CIDR addressing. -- "If there's one thing we've established over the years, it's that the vast majority of our users don't have the slightest clue what's best for them in terms of package stability." -- Gentoo Developer Ciaran McCreesh
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