[GRAYMAIL] Change dhcp-client-identifier

[Patrick Trapp]

You should not have to change the subnet just to increase the available addresses. You would have to configure routes to accommodate, but you could use anything and combine them as a shared network. (I believe so, counting on more experienced folk to correct me if I'm wrong.)


> On Nov 28, 2016, at 6:45 AM, Thomas Zenz <thomas.zenz at oenb.at> wrote:
> 
> Thank you Patrik.
> 
> I hoped I could work arround the change of the IP Subnet. But if I
> cannot change the Client-Identifier, ther is no other way.
> 
> Yes the Cisco VPN appliance changes the ID.
> To answer the suggestion of perl-list. The MAC Address of the Client is
> allways the Addrss of the VPN Concentrator :(
> 
> In the first step I reduces the lease time from 8h to 1h.
> 
> OK
> I will change the subnet...
> 
> Best wishes and peaceful Christmas
> Thomas
> 
> ________________________________
> From: dhcp-users [dhcp-users-bounces at lists.isc.org] on behalf of
> 
> It sounds like the VPN appliance is going to interfere with simply
> identifying the client by MAC, is that right?
> 
> What is your DHCP lease time? You mention "if you connect three times in
> an hour, you get three leases" - does that mean your leases are good for
> an hour? (I don't think that's unreasonable for VPN, but it might be
> shorter than you want once this other issue is worked out.)
> 
> When you say you have more VPN clients, how many more? What percentage
> do you anticipate being connected at the same time? If you are
> increasing your number of clients and/or connected clients
> significantly, have you considered just increasing your VPN address
> pool. You would not have to abandon the existing pool - you could create
> a shared network entry with a new subnet, creating a larger pool without
> having to restructure your existing IP scheme.
> 
> Otherwise, I can't offer any guidance. I have not needed to resort to
> manipulation of client-id to assign addresses and do not know what your
> options are there.
> 
> I really think I would be looking hard at the Cisco appliance to make
> sure you don't have an option to modify its behavior.
> 
> All the best,
> Patrick
> 
> ________________________________
> From: dhcp-users [dhcp-users-bounces at lists.isc.org] on behalf of
> perl-list [perl-list at network1.net]
> Sent: Wednesday, November 23, 2016 7:42 AM
> To: Users of ISC DHCP
> Subject: Re: Change dhcp-client-identifier
> 
> If you have foreknowledge of the MAC address, you could assign static IP
> based on the mac address like so:
> 
> host SomeHost { hardware ethernet 00:01:02:03:04:05; fixed-address
> 10.0.10.2; }
> 
> which would then make it not matter what their dhcp-client-identifier is...
> 
> ________________________________
> From: "Thomas Zenz" <thomas.zenz at oenb.at>
> To: dhcp-users at lists.isc.org
> Sent: Wednesday, November 23, 2016 7:08:55 AM
> Subject: Change dhcp-client-identifier
> Sorry, I did not get the answer via mail, so I resend the Mail like this:
> 
> 
> Sorry, I did not get the answer via mail, so I resend the Mail like this:
> 
> Hi Patrick,
> 
> I agree with you, that DHCP is not the cause of the issue. But, as
> allways, we are the ones who can fix it ;) Can we?
> 
> We do have more VPN clients. That's why we had to look into this problem.
> 
> Regards
> Thomas
> 
> ###################################################
> 
> It sounds like something changed recently - new VPN appliance? More VPN
> clients?
> 
> It might be useful to include that in the conversation because it
> doesn't sound like ISC DHCP is the cause of the issue, just where it's
> become visible.
> 
> Patrick
> 
> ###################################################
> 
> Dear all,
> 
> We are running isc dhcp for years now.
> In the last weeks the count of vpn clients is growing. We only planned a
> /24 network. That would be ok if there wasn't the cisco logic of
> creating the dhcp-client-identifier.  Cisco takes his own Mac-address,
> adds the PCName and here comes the problem, a random number...
> So my Client uses 17 Leases!
> I reduced the lease-time to 1h but still, if a usere reconnects 3 times
> in one hour, it uses 3 addreses.
> 
>  uid "\000cisco-881d.fc6f.affe-NB326973851-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973852-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973857-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973858-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973861-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973863-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973848-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973850-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973853-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973854-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973873-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973859-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973865-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973866-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973868-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973869-inside\000";
>  uid "\000cisco-881d.fc6f.affe-NB326973870-inside\000";
> 
> I tried to change the uid like this:
> on commit {
>   set myClientID = pick (option dhcp-client-identifier,0);
>   log (info, concat ("ClientID: ",myClientID));
> but it looks like the option is no string... (from the log)
> dhcpd: ClientID: HPs2,
> dhcpd: ClientID: HPs2,
> dhcpd: ClientID: fÚAi
> dhcpd: ClientID: HPsY
> dhcpd: ClientID: HPsW¬
> dhcpd: ClientID: lbmw&
> dhcpd: ClientID: lbmw&
> dhcpd: ClientID: HPsY
> dhcpd: ClientID: HPsY
> dhcpd: ClientID: HPsY
> dhcpd: ClientID: HPsY
> dhcpd: ClientID: HPs3T
> dhcpd: ClientID: HPsW¬
> dhcpd: ClientID: HPsW¬
> dhcpd: ClientID: HPs\
> dhcpd: ClientID: HPs\
> 
> I tried to do it like this:
>        if (binary-to-ascii(10,8,".",packet(24,3)) = "192.168.1" ) {
>             set vpnClientID = concat(substring(myClientID,26,6),"-inside");
>             set dhcp-client-identifier = vpnClientID;
>             log (info, concat ("vpnClientID: ",vpnClientID));
>        }
> This is also not working. I use a similar option to choose the PXE Bootfile.
> 
> Please help
> Kind Regards
> Thomas
> 
> 
>