IPv4 Private Address Space
Bob Harold
rharolde at umich.edu
Thu May 13 13:43:56 UTC 2021
At the University of Michigan, the smaller DHCP servers use about 100mb of
ram for the dhcpd process. The largest servers use about 350mb ram to
serve 270,000 dynamic DHCP addresses.
So a difference of 250mb ram looks like about 1kb ram per IP address in the
DHCP ranges, would be my guess. (Did I get that right?)
--
Bob Harold
DNS and DHCP Hostmaster - UMNet
Information and Technology Services (ITS)
rharolde at umich.edu 734-512-7038
On Wed, May 12, 2021 at 3:06 PM Philippe Maechler <plcmaechler at gmail.com>
wrote:
> sorry to hijack this thread. i often read about the memory usage when one
> uses larger subnets/ranges.
>
> what are larger subnets?
>
> at $dayjob we use lots of /24, several hundreds /30 and about two dozens
> /20. the memory usage on a recent server is ignorable and the startup times
> are also way below one minute...
>
> how is it with dhcpv6? there we have even larger pools with ia-na, -pd and
> -ta. is the memory "setup" different?
>
> tia
> philippe
>
> Simon Hobson <dhcp1 at thehobsons.co.uk> schrieb am Mi., 12. Mai 2021, 14:22:
>
>> Louis Garcia <louisgtwo at gmail.com> wrote:
>>
>> >> According to standards set forth in Internet Engineering Task Force
>> >> (IETF) document RFC-1918, the following IPv4 address ranges are
>> reserved by the IANA for private internets,
>> >>
>> >> 10.0.0.0/8 IP addresses: 10.0.0.0 – 10.255.255.255
>> >> 172.16.0.0/12 IP addresses: 172.16.0.0 – 172.31.255.255
>> >> 192.168.0.0/16 IP addresses: 192.168.0.0 – 192.168.255.255
>>
>> Correct.
>> But just because 172.16.0.0/12 is reserved doesn't mean you have to use
>> all 1,048,576 addresses in that block, and you don't have to use /12 as
>> your mask. The /12 here simply tells you that everything from 172.16.0.0 to
>> 172.31.255.255 is in that reserved space.
>> The DHCP server will not allocate anything you haven't told it to, and
>> your border routers (and certainly your ISP) should be filtering any of
>> these RFC1918 address out - "nothing out, nothing in" should be the policy
>> for them.
>> Also, because of the way the server works, it's a really bad idea to
>> create large blocks (though I think relates to ranges, rather than subnets)
>> as it makes in-memory tables huge.
>>
>>
>> >> dhcpd does not seem to like subnet/mask combination.
>> >>
>> >> authoritative;
>> >> default-lease-time 600;
>> >> max-lease-time 7200;
>> >> subnet 172.16.4.0 netmask 255.240.0.0 {
>> >> option domain-name-servers 172.16.4.1;
>> >> option broadcast-address 172.31.255.255;
>> >> option routers 172.16.4.1;
>> >> option ntp-servers 172.16.4.1;
>> >> range 172.16.4.50 172.16.4.254;
>> >> }
>>
>> Yes, as already mentioned, that's not a valid address & mask.
>>
>>
>> > Currently I have three networks 172.16.2.0/24 172.16.3.0/24
>> > 172.16.4.0/24. I read that not all of 172.16.0.0 is private, only
>> > 172.16.0.0/12. I am trying to not have public routable IPs on my
>> > network. Please let me know if this setup is fine.
>> >
>> > # DHCP Server Configuration file.
>> >
>> > authoritative;
>> > default-lease-time 600;
>> > max-lease-time 7200;
>> >
>> > # Client system architecture type: RFC4578
>> > option arch code 93 = unsigned integer 16;
>> >
>> > subnet 172.16.2.0 netmask 255.255.255.0 {
>> > option domain-name-servers 172.16.2.1;
>> > option broadcast-address 172.16.2.255;
>> > option routers 172.16.2.1;
>> > option ntp-servers 172.16.2.1;
>> > range 172.16.2.50 172.16.2.254;
>> > if option arch = 00:07 {
>> > filename "/grub/shim.efi";
>> > }
>> > next-server 172.16.2.5;
>> > }
>> >
>> > subnet 172.16.3.0 netmask 255.255.255.0 {
>> > option domain-name-servers 172.16.3.1;
>> > option broadcast-address 172.16.3.255;
>> > option routers 172.16.3.1;
>> > option ntp-servers 172.16.3.1;
>> > range 172.16.3.50 172.16.3.254;
>> > }
>> >
>> > subnet 172.16.4.0 netmask 255.255.255.0 {
>> > option domain-name-servers 172.16.4.1;
>> > option broadcast-address 172.16.4.255;
>> > option routers 172.16.4.1;
>> > option ntp-servers 172.16.4.1;
>> > range 172.16.4.50 172.16.4.254;
>> > }
>>
>> Yes, that's just fine.
>>
>>
>>
>> Simon
>>
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> _______________________________________________
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>
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