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Today's Topics:
1. DHCPv6 and on_commit etc events (perl-list)
2. Re: [Bug Report] key conflict message for create host by
Omapi (John Wobus)
3. Re: 20 minute leases (John Wobus)
----------------------------------------------------------------------
Message: 1
Date: Fri, 30 Oct 2015 10:15:52 -0400 (EDT)
From: perl-list <[email protected]>
To: Users of ISC DHCP <[email protected]>
Subject: DHCPv6 and on_commit etc events
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=utf-8
ISC DHCP version: 4.3.3
I need some help in finding information about what sort of options are
available in in on_ events in DHCPv6. I can't seem to find any man pages or so
on that describe what can be logged with these events (on commit, on expiry, on
release). I have things being logged for DHCPv4 like so:
on commit {
log( error,
concat( "LEASED,",
"ip,", binary-to-ascii (10, 8, ".", leased-address),",",
"time,",binary-to-ascii(10,32,"",encode-int (lease-time,32)),",",
"hardware,",binary-to-ascii(16,8,":",substring(hardware,1,7))
)
);
}
on expiry {
log( error,
concat( "LEASEEXPIRY,",
"ip,", binary-to-ascii (10, 8, ".", leased-address)
)
);
}
on release {
log( error,
concat( "RELEASED,",
"ip,", binary-to-ascii (10, 8, ".", leased-address),",",
"hardware,",binary-to-ascii(16,8,":",substring(hardware,1,7))
)
);
}
Would like to do something similar in DHCPv6. Have begun testing with on
commit. Apparently the same sorts of data are not available as the same on
commit { } directive from above produces these log messages:
Oct 30 13:58:45 DHCPserver dhcpd: data: "leased-address" configuration
directive: there is no lease associated with this client.
Oct 30 13:58:45 DHCPserver dhcpd: data: leased_lease: not available
Oct 30 13:58:45 DHCPserver dhcpd: data: hardware: no raw packet or lease is
available
I realize the hardware address is probably not available as these packets are
being relayed from a router that does not support RFC 6939 (are there any that
do?).
Mainly, I'd like to see a man page or some sort of document that describes what
IS available ... or some config I could drop in my dhcpd.conf that would log
what is available or something... any ideas?
------------------------------
Message: 2
Date: Fri, 30 Oct 2015 16:05:32 -0400
From: John Wobus <[email protected]>
To: Users of ISC DHCP <[email protected]>
Subject: Re: [Bug Report] key conflict message for create host by
Omapi
Message-ID: <[email protected]>
Content-Type: text/plain; charset=windows-1252
On Oct 29, 2015, at 7:47 AM, Simon Hobson <[email protected]> wrote:
> Muhammad Faisal <[email protected]> wrote:
>
>> The DHCP experts might explain this but what about arp resolution within the
>> server ? The MAC address is a unique identifier so if your deployment is
>> getting two IP for the same MAC how the conflict will resolve?
>
> The assumption is that the client won't be in two places at once - so
> wherever it is located at any point in time, ARP will work fine and there's
> no conflict.
>
> However, a device with a single MAC address can have two IP addresses - and
> that'll work fine. Also, though I *REALLY* do not recommend this, you can
> have two clients with the same MAC address in different networks (in
> different collision domains) and IP addressing will work fine - ARP
> resolution within each network will work fine, the MAC address only needs to
> be unique within one collision domain*.
And if the DHCP protocol or server were not to handle this, a client could DOS
another
client using the same DHCP server, even on a separate subnet, simply by using
the victim's
MAC address.
As far as I know, ISC dhcpd serves DHCP for identical MAC addresses on
different subnets,
except for configuring it via the OMAPI interface. It seems reasonable that
dhcpd support
such configuration but I don?t know where that potential enhancement falls on
ISC?s priority list.
John Wobus
Cornell U IT
------------------------------
Message: 3
Date: Fri, 30 Oct 2015 16:24:02 -0400
From: John Wobus <[email protected]>
To: Users of ISC DHCP <[email protected]>
Subject: Re: 20 minute leases
Message-ID: <[email protected]>
Content-Type: text/plain; charset=windows-1252
On Oct 26, 2015, at 10:08 AM, Friesen, Don MTIC:EX <[email protected]>
wrote:
> Hopefully a quick question. We migrated some sites from a few old DHCP
> servers running 4.1.1 to some not as old servers running 4.2.5. The users
> with laptops began complaining about sporadic loss of IP connectivity. They
> noticed they were getting 20 minutes leases instead of 24 hour leases. I
> watched the traffic and it seems all initial leases to unknown MAC addresses
> get a 20 minute lease and on renewal get the 24 hour lease. This is not a
> complaint, I like the idea of a trial lease. I just want to verify that the
> 4.1.1 version did not have this behavior without having to recreate that
> environment. I?d like to explain the behaviour to my users with a degree of
> confidence.
>
> Don Friesen
As others have pointed out, this is a feature of failover,
and I?ve been observing that for at least a decade.
The actual interval is configured (?mclt"), so a configuration
change could have changed the behavior.
In our own case, we saw sporadic renewal-failures when our
DHCP servers became overloaded. If that is the case
or packets are being lost for other reasons, IP addresses
can be lost. Correct client behavior tries renewals
multiple times so the underlying problem can grow a
while and remain unnoticed.
DHCP service is disk-bound so a new server setup lacking
previous disk performance (e.g. previous tuning or performance
features) could affect the DHCP service reliability. As could
disk contention such as using syncing syslog for the DHCP log.
John Wobus
Cornell U IT
------------------------------
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