Linux DHCP sending wrong parameters in offer packet
Sten Carlsen
stenc at s-carlsen.dk
Fri Jan 25 19:39:52 UTC 2019
I take it that classes work like host declarations that inherit
parameters from where they are defined and that can be very incorrect in
a given situation?
On 25/01/2019 17.37, Thomas Markwalder wrote:
> Hello
>
> As others have pointed out, classes must only be defined globally.
> Defining them within subnets or networks is not supported and it can
> have odd effects on statement execution/option values. The
> configuration parser currently does not complain when you do this but
> it probably should. We will very likely add at least a warning if not
> an error for this.
>
> Regards,
>
> Thomas Markwalder,
> ISC Software Engineering
>
> On 1/25/19 11:29 AM, perl-list wrote:
>> Class should be global, I believe. That is my understanding anyway.
>> You shouldn't have them inside of a subnet {} or shared-network {}
>> statement. The limiting occurs with the match if statement. That is
>> my understanding anyways.
>>
>> ------------------------------------------------------------------------
>>
>> *From: *"Gaikwad Yogesh" <Yogesh.Gaikwad at tieto.com>
>> *To: *"Users of ISC DHCP" <dhcp-users at lists.isc.org>
>> *Sent: *Friday, January 25, 2019 9:43:48 AM
>> *Subject: *RE: Linux DHCP sending wrong parameters in offer packet
>>
>> Hi Glenn,
>>
>> I followed Cisco documentation on below link to configure the
>> option 43 for Cisco AP's:
>>
>> https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/97066-dhcp-option-43-00.html
>>
>>
>> There are two parts to this config, one is in the global config,
>> and other part sits inside the subnet.
>>
>> Below lines are in the global configuration
>>
>> # CISCO OPTION 43
>> option space Cisco_LWAPP_AP;
>> option Cisco_LWAPP_AP.server-address code 241 = array of ip-address;
>>
>>
>> And then below is the subnet configuration
>>
>> subnet 10.56.20.0 netmask 255.255.255.0 {
>> option routers 10.56.20.1;
>> option subnet-mask 255.255.255.0;
>> option broadcast-address 10.56.20.255;
>> default-lease-time 43200;
>>
>> class "Cisco AP c3800" {
>>
>> match if option vendor-class-identifier = "Cisco AP c3800";
>> option vendor-class-identifier "Cisco AP c3800";
>> vendor-option-space Cisco_LWAPP_AP;
>> option Cisco_LWAPP_AP.server-address 10.140.1.1; }
>>
>> pool {
>> failover peer "te-failover";
>> deny dynamic bootp clients;
>> range 10.56.20.10 10.56.20.250;
>> }
>> }
>>
>>
>>
>> We have several such subnets configured which have this 'class
>> "Cisco AP c3800"' configuration inside the subnets, the above
>> mentioned subnet sits at the end of the dhcpd.conf file.
>>
>> I understood your concern to have it configured globally, but
>> then what if I want to have a different
>> 'Cisco_LWAPP_AP.server-address' for different subnets?
>>
>>
>>
>> Best regards,
>>
>> Yogesh Gaikwad, Technical Architect - TECA Network
>>
>> Tieto Corporation, TSM
>>
>> -----Original Message-----
>> From: dhcp-users [mailto:dhcp-users-bounces at lists.isc.org] On
>> Behalf Of Glenn Satchell
>> Sent: Friday, January 25, 2019 7:45 PM
>> To: Users of ISC DHCP <dhcp-users at lists.isc.org>
>> Subject: Re: Linux DHCP sending wrong parameters in offer packet
>>
>> Hi Yogesh,
>>
>> Without seeing hyour config file I can guess that the option 43
>> setting should be set in the global configuration rather than
>> inside one of your subnets. Setting it inside the subnet causes
>> inheritance of those subnet values.
>>
>> To confirm, could you please post your dhcpd.conf? If it is is
>> very large perhaps you might post the relevant parts.
>>
>> regards,
>> -glenn
>> --
>> Glenn Satchell mailto:glenn.satchell at uniq.com.au | Today is
>> the past
>> Uniq Advances Pty Ltd http://www.uniq.com.au | that
>> people in
>> Mobile 0409 458 580 | the
>> future will
>> Member IT Professionals Association www.itpa.org.au | dream about.
>>
>> On Fri, January 25, 2019 11:41 pm, Gaikwad Yogesh wrote:
>> > Hi,
>> >
>> >
>> > There is issue that linux DHCP is sending wrong parameters while
>> > sending offer packet for Cisco AP's in one of our office locations.
>> >
>> > I have taken packet captures on the DHCP server side.
>> >
>> >
>> > As you can see in below packet capture there is DHCP DISCOVER
>> message
>> > from Cisco AP requesting for IP and other parameters.
>> >
>> > Then in DHCP offer packet, it offers IP from correct subnet,
>> but with
>> > wrong router IP, subnet mask and broadcast address.
>> >
>> > Basically, my observation is that it is giving wrong parameters in
>> > offer from the topmost subnet (as linux works from top to bottom
>> > approach) that has cisco option 43 configured. If I remove the
>> Cisco
>> > option 43 from that subnet then it provides parameters from next
>> > subnet which has the Cisco option 43 in it.
>> >
>> > The correct subnet from which I am expecting that the AP should
>> get
>> > all its parameters is configured at the end of the DHCP conf file.
>> >
>> >
>> > DHCP DISCOVER PACKET
>> >
>> >
>> > [cid:image001.png at 01D4B4D9.6F320900]
>> >
>> >
>> >
>> > DHCP OFFER PACKET
>> >
>> >
>> > [cid:image002.png at 01D4B4D9.6F320900]
>> >
>> >
>> >
>> >
>> >
>> > Best regards,
>> >
>> >
>> > Yogesh Gaikwad, Technical Architect - TECA Network
>> >
>> >
>> > Tieto Corporation, TSM
>> >
>> >
>> > email Yogesh.Gaikwad at tieto.com<mailto:Yogesh.Gaikwad at tieto.com>,
>> > direct
>> > +91 (0)2067303120
>> > Wing 1, Cluster D, EON Free Zone, MIDC Kharadi Knowledge Park,
>> Pune -
>> > 411 014, India
>> >
>> >
>> > [Tieto_logo_for_email_signature_127x50]<http://www.tieto.com/>
>> >
>> >
>> > Please note: The information contained in this message may be
>> legally
>> > privileged, confidential and protected from disclosure. If you
>> > received this in error, please notify the sender immediately and
>> > delete the message from your computer. Thank you.
>> >
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>> >
>> >
>>
>>
>>
>>
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