configuration option data not in file
dhcp at thehobsons.co.uk
Wed Jun 14 08:25:52 UTC 2006
<sandeep.vashisht at wipro.com> wrote:
>if we dont have any data for a particular option in the DHCP SERVER
>Can somebody tell me then how the server is expected to behave ?
>How the server will respond to the client?
>Will it send the garbage values or will it drop the complete request.
It depends on what is missing.
Some options, such as default, min, max lease times will have default values.
Some options could be inferred - eg ddns-domainname has an algorithm
used to try and infer a value if not specified.
Most options are simply 'not present' if not specified. Should a
client request an options list that includes missing options, the
server will simply ignore the ones it hasn't got. This is actually
the case most of the time with common clients such a Mac OS X and
Windows - both request options that are generally not configured.
For example, renewing the lease on my Mac, I see a request with :
Option 53: DHCP Message Type = DHCP Request
Option 55: Parameter Request List
1 = Subnet Mask
3 = Router
6 = Domain Name Server
15 = Domain Name
112 = NetInfo Parent Server Address
113 = NetInfo Parent Server Tag
78 = Directory Agent Information
79 = Service Location Agent Scope
95 = Lightweight Directory Access Protocol
Unknown Option Code: 252
Option 57: Maximum DHCP Message Size = 1500
Option 61: Client identifier
Hardware type: Ethernet
Client MAC address: AppleCom_xx:xx:xx (00:0a:95:xx:xx:xx)
Option 50: Requested IP Address = 192.168.1.37
Option 51: IP Address Lease Time = 90 days
Option 12: Host Name = "xxxxxxxxxxxxxxxxxxx"
And a reply (from a windows dhcp server) with :
Option 53: DHCP Message Type = DHCP ACK
Option 58: Renewal Time Value = 4 days
Option 59: Rebinding Time Value = 7 days
Option 51: IP Address Lease Time = 8 days
Option 54: Server Identifier = 192.168.1.250
Option 1: Subnet Mask = 255.255.255.0
Option 3: Router = 192.168.1.250
Option 6: Domain Name Server = 192.168.1.250
Option 15: Domain Name = "xxxxxxxxxxxxxxx.local"
One of the tests a client should be doing when deciding which (if
any) offer to accept is to decide if the options available in the
offer are sufficient for it's needs. If there are multiple offers,
then logically it should be taking the one that offers the fullest
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