# Rules for creating DHCP Options 43 or 125

Although not recommended, string values for Options 43 and 125 can be entered from scratch into the DHCP Options form. The preferred entry method for Option 125 is to use the Mitel Tags fields in the form. Using the fields guarantees a correctly formatted string.

The information is entered as a sequence of tag/value pairs separated by semi-colons. The tags are the names in parentheses under Tag Value— e.g., sw_tftp, call_srv, vlan, etc. Enter the names exactly as they appear followed by an equals sign (=), and a value in the required format. See descriptions for Tag Value below for valid values.

Follow these rules when entering the tag/value pairs:

- The maximum string size is 250 characters for Option 125 and 253 for Option 43 with encapsulation or 255 without.

- The string must always start with the "id:ipphone.mitel.com;".

- Tag/value pairs may appear in any order. If there is a repeat, the later pair takes precedence provided it has a value.

- The string is case sensitive.

- All integer values are decimal encoded (no hex or binary).

- All IP address and address mask values are assumed to be IPv4, encoded in dot-decimal notation (xxx.xxx.xxx.xxx). Leading 0s are permitted but not required.

- Host fully qualified domain names (FQDNs) are encoded as "<host>.<domain>" or by IP address as above. File paths at a particular host may be encoded as "<FQDN>/<path>. Specific port can be indicated by "<FQDN>:<port>".

- Null values in the configuration line (e.g., "<tag>=") are not allowed. Option 125 configuration lines created in the DHCP Options form are automatically stripped of any null value tags.

- Spaces for legibility are allowed in the string only between tag/value pairs (e.g., at separators) or at beginning or end of line.

- Final separator is allowed, but not required.

- Multiple back-to-back separators are permitted, and are ignored (eg. ";;<tag/value>" is OK).