multi interfaces(vlans) configuration

Steve van der Burg Steve.vanderBurg at lhsc.on.ca
Thu Oct 8 12:00:53 UTC 2020


I'm serving leases from a total lease pool that has about a quarter of a million leasable addresses, with about 30k active leases at any one time.  Most lease lengths are 60 hours (2.5 days) and those are all being served from a pair of single-CPU virtual machines (running Debian 10) with 2GB RAM each.  And each one isn't really breaking a sweat.  I rarely see more than 20% CPU usage and more than 75% of RAM used by dhcpd.

As Glenn said, lease length can make a big difference with regards to total traffic, CPU load, etc, but with lease lengths like mine you can see that you don't need much in the way of hardware.

...Steve

-----Original Message-----
From: dhcp-users <dhcp-users-bounces at lists.isc.org> On Behalf Of Ahiya Zadok
Sent: Thursday,October 08,2020 4:03 AM
To: Users of ISC DHCP <dhcp-users at lists.isc.org>
Subject: RE: multi interfaces(vlans) configuration

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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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