multi interfaces(vlans) configuration

Thu Oct 8 23:27:19 UTC 2020

ISC dhcpd needs to access the raw ethernet interface, so doesn't play 
well with vlan sub-interfaces.

You don't have 256 different dhcp servers, only one. Typically in the 
router each interface definition will include a dhcp relay or 
ip-forwarder, and this will always be the same the single IP address of 
your dhcp server.

If that doesn't work you may be able to set the dhcp relay in your 
switches as an alternative.

regards,
Glenn

On 2020-10-09 01:25, Ahiya Zadok wrote:
> Thanks
> 
> The network gear in my sites is the bottleneck
> It supports up to 256 DHCP servers/relay agents.
> Do you think that raspberry pi could handle 500 VLAN interfaces?
> 
> 
> -----Original Message-----
> From: dhcp-users <dhcp-users-bounces at lists.isc.org> On Behalf Of Steve 
> van
> der Burg
> Sent: Thursday, October 8, 2020 3:20 PM
> To: Users of ISC DHCP <dhcp-users at lists.isc.org>
> Subject: RE: multi interfaces(vlans) configuration
> 
> In my case (and in nearly all cases?) the DHCP traffic from the clients 
> on
> those VLANs is being forwarded to the DHCP servers by the network gear. 
>  I
> don't run ours, but I know that our network people have added "DHCP 
> helper
> address" settings to all (checking...) 2530 subnets.  It all arrives on
> one interface on each of my DHCP servers.  I can't imagine having 2500
> virtual interfaces on either of those.
> 
> ...Steve
> 
> -----Original Message-----
> From: dhcp-users <dhcp-users-bounces at lists.isc.org> On Behalf Of Ahiya
> Zadok
> Sent: Thursday,October 08,2020 8:08 AM
> To: Users of ISC DHCP <dhcp-users at lists.isc.org>
> Subject: RE: multi interfaces(vlans) configuration
> 
> CAUTION: This email originated from outside the organization. Do not 
> click
> links or open attachments unless you recognize the sender and know the
> content is safe.
> 
> 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
> 
> CAUTION: This email originated from outside the organization. Do not 
> click
> links or open attachments unless you recognize the sender and know the
> content is safe.
> 
> 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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