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[STDS-802-Privacy] On the DHCP client identifier



Hi,

Yesterday during the call there was some discussion on whether the DHCP
client identifier (which we have been using on the trials to ensure the
same IP address is leased to a client even if it changes its MAC
address, just for the sake of having more information about trial
participants) is an optional or mandatory field.

I've checked it and it is optional. RFC 2131 says:

"DHCP defines a new 'client identifier' option that is used to pass an
 explicit client identifier to a DHCP server.  This change eliminates
 the overloading of the 'chaddr' field in BOOTP messages, where
 'chaddr' is used both as a hardware address for transmission of BOOTP
 reply messages and as a client identifier.  The 'client identifier'
 is an opaque key, not to be interpreted by the server; for example,
 the 'client identifier' may contain a hardware address, identical to
 the contents of the 'chaddr' field, or it may contain another type of
 identifier, such as a DNS name.  The 'client identifier' chosen by a
 DHCP client MUST be unique to that client within the subnet to which
 the client is attached. If the client uses a 'client identifier' in
 one message, it MUST use that same identifier in all subsequent
 messages, to ensure that all servers correctly identify the client."

I've also looked at what my Linux box does. Unless I specify a value
for the dhcp-client-identifier, DHCP requests does not include this
option. If I explicitly indicate an identifier, it is included in the
requests.

Thanks,

Carlos