Failover peer outside pools?

classic Classic list List threaded Threaded
4 messages Options
Reply | Threaded
Open this post in threaded view
|

Failover peer outside pools?

Nicolas Ecarnot
Hello,

All our subnets are behind routers that have ip helpers, redirecting
DHCP requests towards 2 dhcp servers in failover peers (we have around
10 DHCP servers in couples).

In our setup, I just noticed that amongst our hundreds of
shared-networks using failover peers, some subnets have a strange
configuration :

I saw that in some rare cases, we have some subnets with *no* pool, thus
*no* failover setup, where there's just one static reservation declared,
and it is working.
But I was wondering how it goes?
- when the host is requesting some DHCP traffic, it is broadcasted via
the router towards 2 DHCP server that have no idea about what the other
did some hours ago in this subnet
- as the only request is about a static ip, I guess any of both server
is answering correctly, but not telling the other.

So I'm embarrassed that the router is broadcasting the DHCP traffic to 2
servers that don't talk (about this particular subnet - there are
chatting about others).

The documentation seems to imply that failover definition lies only
inside pools.
I could create a pool just to add failover context, but the same doc
also states that static reservation should stay outside pools.

Am I missing something?

--
Nicolas ECARNOT
_______________________________________________
dhcp-users mailing list
[hidden email]
https://lists.isc.org/mailman/listinfo/dhcp-users
Reply | Threaded
Open this post in threaded view
|

Re: Failover peer outside pools?

Simon Hobson
Nicolas Ecarnot <[hidden email]> wrote:

> In our setup, I just noticed that amongst our hundreds of shared-networks using failover peers, some subnets have a strange configuration :
>
> I saw that in some rare cases, we have some subnets with *no* pool, thus *no* failover setup, where there's just one static reservation declared, and it is working.

That's not strange - it's normal.
As long as both servers have the same data, then both will reply (to broadcast requests) with the same offers - the client can accept either and get the same config.

So no problem.



_______________________________________________
dhcp-users mailing list
[hidden email]
https://lists.isc.org/mailman/listinfo/dhcp-users
Reply | Threaded
Open this post in threaded view
|

Re: Failover peer outside pools?

Graham Clinch
In reply to this post by Nicolas Ecarnot
Hi Nicolas,

> I saw that in some rare cases, we have some subnets with *no* pool, thus
> *no* failover setup, where there's just one static reservation declared,
> and it is working.
> But I was wondering how it goes?
> - when the host is requesting some DHCP traffic, it is broadcasted via
> the router towards 2 DHCP server that have no idea about what the other
> did some hours ago in this subnet
> - as the only request is about a static ip, I guess any of both server
> is answering correctly, but not telling the other.

Assuming both servers have the same configuration for the static
allocations, all is good.  In fact, your dhcpd.leases file will only
ever contain leases that were dynamically assigned by the server (i.e.
from a 'range'), because the configuration file already defines all the
information required to correctly match a client to a 'host'
fixed-address (and although the server advertises a lease time to the
client, it doesn't bother recording that expiry time, because when even
when the lease expires, the address is still restricted to just that
client).

> So I'm embarrassed that the router is broadcasting the DHCP traffic to 2
> servers that don't talk (about this particular subnet - there are
> chatting about others).
>
> The documentation seems to imply that failover definition lies only
> inside pools.
> I could create a pool just to add failover context, but the same doc
> also states that static reservation should stay outside pools.

For networks without any dynamic addresses, we don't bother generating
an empty pool (I seem to remember that empty pools are considered a
configuration error).

The 'RESERVED LEASES' section of dhcpd.conf's manpage might be
interesting reading?

In short, I don't think there is anything wrong with your configuration.

Graham
_______________________________________________
dhcp-users mailing list
[hidden email]
https://lists.isc.org/mailman/listinfo/dhcp-users
Reply | Threaded
Open this post in threaded view
|

Re: Failover peer outside pools?

Nicolas Ecarnot
Le 05/11/2015 11:40, Graham Clinch a écrit :
> For networks without any dynamic addresses, we don't bother generating
> an empty pool (I seem to remember that empty pools are considered a
> configuration error).

OK, I precisely understand how all is working.

Thank you Simon and Graham for your answers.




This setup was made in 2009, and quite forgotten because working.

> In short, I don't think there is anything wrong with your configuration.

Glad to hear it, as this all has been setup up by... me.

--
Nicolas ECARNOT
_______________________________________________
dhcp-users mailing list
[hidden email]
https://lists.isc.org/mailman/listinfo/dhcp-users