multi interfaces(vlans) configuration

glenn.satchell at uniq.com.au glenn.satchell at uniq.com.au
Thu Oct 8 08:37:33 UTC 2020


Hi Ahiya

I'm not sure about memory usage per IP. I seem to vaguely remember that 
having configuration with say a /16 subnet and only a few devices used a 
lot more memory than a smaller subnet like a /24 with the same number of 
devices.

With 24 hour lease a PI4 might get by. Based on a quick calculation of 
my lease file, where I have just under 400 bytes per lease, I think 
you'll need about 2MB for your leases file. This will need to be fast 
storage such as an SSD.

As I said before a PI4 is cheap so you could buy one or two to try in 
that size network. To keep your cost down I guess you could deploy more 
than one PI4 at each site and split the subnet between them to create a 
manageable workload if one PI4 wasn't powerful enough.

With that many subnets and sites I would look at a backend server that 
used a database or spreadsheet to hold the data and a script to generate 
all the configuration files and push them out to the individual servers 
and restart the dhcpd service. That's going to make your life a lot 
easier.

regards,
Glenn

On 2020-10-08 19:02, Ahiya Zadok wrote:
> Thanks, Glenn
> 
> Regarding the number of sites- I plan to have a server per site.
> Each site will have around 500 subnets with around 10-15 devices per
> subnet.
> Does the number of IPs per subnet affect memory even when they are not
> assigned?
> This is MDUs installation so 24H lease is good enough.
> 
> 
> -----Original Message-----
> From: dhcp-users <dhcp-users-bounces at lists.isc.org> On Behalf Of
> glenn.satchell at uniq.com.au
> Sent: Thursday, October 8, 2020 10:54 AM
> To: Users of ISC DHCP <dhcp-users at lists.isc.org>
> Subject: Re: multi interfaces(vlans) configuration
> 
> Hi,
> 
> The size of the server depends on two things - the number of clients 
> and
> how often they renew their lease.
> 
> Eg if they renew once every hour versus once every day then that takes
> 24 times as much cpu reources in the work done to renew the leases and
> record the updates.
> 
> Secondly a large amount of the lease data is kept in memory, so the 
> number
> of lease affects the memory size.
> 
> So, how many sites? You say 500 vlans - which I guess equates to 
> subnets
> - that's what dhcpd configuration needs. And how many devices per 
> subnet
> typically? A subnet doesn't have to be a /24, it can be any size that 
> is
> suitable for that subnet, eg multiple /24 pools, /21 will give 2048
> addresses, /20 will give 4096, or bigger if needed.
> 
> Others running large number of clients, say 10-20k can probably offer
> better advice, but I don't think a PI4 with 8GB is not going to have
> enough memory, cpu or storage I/O.
> 
> You'll probably want a server with 32 or 64GB memory and SSD or NVME 
> disks
> for high throughput. With that many clients then 10 or 25 Gigabit 
> network
> is probably needed too.
> 
> You'll also need to think about what bandwidth you have in your 
> back-haul
> networks back to the central network where the dhcp server is.
> 
> However, a PI4 is cheap so you could try one out to see how it goes.
> 
> regards,
> -glenn
> 
> On 2020-10-08 15:57, ahiya wrote:
>> I'm new to isc/kea.I have multi-sites with around 2000-5000 devices
>> per site.the real issue is that they are spread across 500 different
>> VLANs.I wanted to know is isc/kea is the right solution for that
>> task.and what is the right way to implement it?if the only service I
>> need is dhcp4 serving all these segments, what will be the HW
>> requirements for this task?
>> Raspberry PI4 with 8G mem will be enough?should I use .conf files or
>> should I go for the backend server?ill appreciate any feedback.thanks
>> a lot.
>> 
>> 
>> 
>> --
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