multi interfaces(vlans) configuration

Thu Oct 8 23:15:10 UTC 2020

If you have a router forwarding packets between subnets, then the dhcp 
server only has to be connected to a single vlan - the router can 
forward dhcp broadcasts to the server. So you don't need 500 interfaces 
on your dhcp server.

regards,
-glenn

On 2020-10-08 23:07, Ahiya Zadok wrote:
> Thanks, Steve
> 
> Do you think that the numbers of subnets and the number of interfaces
> (vlans) that DHCP is listening to have much effect on resource
> utilization?
> 
> 
> -----Original Message-----
> From: dhcp-users <dhcp-users-bounces at lists.isc.org> On Behalf Of Steve 
> van
> der Burg
> Sent: Thursday, October 8, 2020 3:01 PM
> To: Users of ISC DHCP <dhcp-users at lists.isc.org>
> Subject: RE: multi interfaces(vlans) configuration
> 
> 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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