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Today's Topics:
1. Fail over serves on different VLANS (Klaus Vink Slott)
2. Re: Fail over serves on different VLANS (/dev/rob0)
3. Re: Fail over serves on different VLANS (Patrick Trapp)
4. Re: Fail over serves on different VLANS (Klaus Vink Slott)
5. Re: Fail over serves on different VLANS (S Ca)
----------------------------------------------------------------------
Message: 1
Date: Thu, 14 Jan 2016 13:18:00 +0100
From: Klaus Vink Slott <[email protected]>
To: Users of ISC DHCP <[email protected]>
Subject: Fail over serves on different VLANS
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"; format=flowed
Hi
We have been running 2 dhcp servers in fail over configuration for quite
a while. Now we consider moving one server to a host in another
building. This will also place the host on another VLAN.
In a earlier tread here John Wobus <[email protected]> wrote:
> As far as I know, DHCP redundancy works by having the servers
> offer different addresses and the client picking one. ISC
> DHCP servers reduce the obvious duplicated effort by having
> one of the two DHCP servers wait a few seconds to see if the
> other server makes an offer. But if the one server doesn't
> pick up on it's peer's offer, the address it offers itself
> is always a different one.
How does the server "see if the other server makes an offer". Do they
need to bee on the same VLAN or is it communicated directly between the
servers?
--
Regards
Klaus Vink Slott
------------------------------
Message: 2
Date: Thu, 14 Jan 2016 06:45:09 -0600
From: /dev/rob0 <[email protected]>
To: [email protected]
Subject: Re: Fail over serves on different VLANS
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
On Thu, Jan 14, 2016 at 01:18:00PM +0100, Klaus Vink Slott wrote:
> How does the server "see if the other server makes an offer". Do
> they need to bee on the same VLAN or is it communicated directly
> between the servers?
The dhcpd servers define a TCP port in their configuration. They
have an internal protocol by which their leases are communicated
directly.
See "CONFIGURING FAILOVER" in the dhcpd.conf(5) manual.
--
http://rob0.nodns4.us/
Offlist GMX mail is seen only if "/dev/rob0" is in the Subject:
------------------------------
Message: 3
Date: Thu, 14 Jan 2016 12:54:35 +0000
From: Patrick Trapp <[email protected]>
To: Users of ISC DHCP <[email protected]>
Subject: Re: Fail over serves on different VLANS
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
Actually, observing network captures in our network, I usually see paired
offers - different addresses, one from each server - and the querying host
picks one and acknowledges it. The other offer expires and gets sent out again
in response to a different request.
I don't think moving your second host to a new VLAN should necessarily be cause
for concern as long as the two servers can communicate with each other.
Better to test to be sure, of course.
Patrick
> On Jan 14, 2016, at 6:18 AM, Klaus Vink Slott <[email protected]> wrote:
>
> Hi
>
> We have been running 2 dhcp servers in fail over configuration for quite a
> while. Now we consider moving one server to a host in another building. This
> will also place the host on another VLAN.
>
> In a earlier tread here John Wobus <[email protected]> wrote:
> > As far as I know, DHCP redundancy works by having the servers
> > offer different addresses and the client picking one. ISC
> > DHCP servers reduce the obvious duplicated effort by having
> > one of the two DHCP servers wait a few seconds to see if the
> > other server makes an offer. But if the one server doesn't
> > pick up on it's peer's offer, the address it offers itself
> > is always a different one.
>
> How does the server "see if the other server makes an offer". Do they need to
> bee on the same VLAN or is it communicated directly between the servers?
>
> --
> Regards
> Klaus Vink Slott
> _______________________________________________
> dhcp-users mailing list
> [email protected]
> https://lists.isc.org/mailman/listinfo/dhcp-users
------------------------------
Message: 4
Date: Thu, 14 Jan 2016 15:19:29 +0100
From: Klaus Vink Slott <[email protected]>
To: <[email protected]>
Subject: Re: Fail over serves on different VLANS
Message-ID: <[email protected]>
Content-Type: text/plain; charset="windows-1252"; format=flowed
Den 14-01-2016 kl. 13:45 skrev /dev/rob0:
> On Thu, Jan 14, 2016 at 01:18:00PM +0100, Klaus Vink Slott wrote:
>> How does the server "see if the other server makes an offer". Do
>> they need to bee on the same VLAN or is it communicated directly
>> between the servers?
>
> The dhcpd servers define a TCP port in their configuration. They
> have an internal protocol by which their leases are communicated
> directly.
>
> See "CONFIGURING FAILOVER" in the dhcpd.conf(5) manual.
Thanks. I have been searching the manual - but did not find any
information on which information is shared over the communication
channel. However digging in once more I found "load balance max seconds"
which suggest that time since the the first DHCPDISCOVER or DHCPREQUEST
is used if the communication channel is not reliable.
As the dhcphelper distributes DHCPDISCOVER to both server I guess my
worries has no reason.
--
Thanks
Klaus
------------------------------
Message: 5
Date: Thu, 14 Jan 2016 15:45:26 +0000
From: S Ca <[email protected]>
To: Users of ISC DHCP <[email protected]>
Subject: Re: Fail over serves on different VLANS
Message-ID:
<CALMep05OHBU=t4sg27aG2gvv+qdcBwuKufLTuaX868GJCA=v...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On 14 January 2016 at 12:18, Klaus Vink Slott <[email protected]> wrote:
> How does the server "see if the other server makes an offer". Do they need
> to bee on the same VLAN or is it communicated directly between the servers?
The client broadcasts it's DHCPREQUEST in which it states which server
it has chosen, those packets are then forwarded by the IP helpers to
both DHCP failover peers.
DHCP failover doesn't need both peers to be in the same VLAN, the only
requirement is that the IP helper sends to both peers simultaneously.
Steve
------------------------------
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