DHCP Option 43 is a bit of an odd beast. Vendors can treat it however they want - some expect the option numbers to match with the DHCP option numbers, others do not.
The basic structure is 1 byte for an option ID, 1 byte for the length of the option data (n), then n bytes of the actual option data - and, rinse and repeat.
Let's take the example from dhcp-options. They've stuck the newlines in strategic places to make it easier to read. In reality, the setting they've configured is just this:
02:04:AC:11:41:01:03:12:73:75:6e:64:68:63:70:2d:73:65:72:76:65:72:31:37:2d:31:04:12:2f:65:78:70:6f:72:74:2f:72:6f:6f:74:2f:69:38:36:70:63;
Which is pretty hard to read unless you know what you're looking for. Let's break down the parts:
- Byte 1,
0x02. This says that this block is config for option number 2. How that's interpreted is up to the vendor.
- Byte 2,
0x04. This says that the data for option 2 will occupy the next 4 bytes.
- Bytes 3-6,
0xAC114101. These four bytes are the actual data. As you saw when you tried to decode it, it's not readable data.
- Byte 7, the start of the next option block,
0x03. The whole chain starts over again, this says that the following config is for option 3.
- and so on, for 3 sections
Another example, from the snom wiki page:
42:0c:68:74:74:70:3a:2f:2f:74:65:73:74:00:43:12:73:6e:6f:6d:2f:73:65:74:74:69:6e:67:73:2e:70:68:70:00;
- Byte 1,
0x42. 42 in hex is 66, for option code 66.
- Byte 2,
0x0c. Length of 12 bytes.
- Bytes 3-14,
0x687474703a2f2f7465737400. This is http://test with a null byte (0x00) on the end. Not sure why they have that there.
- Byte 15,
0x43. Option 67.
- Byte 16,
0x12. 18 byte length.
- Bytes 17-34,
0x736e6f6d2f73657474696e67732e70687000. snom/settings.php. Again, the null byte at the end.
So, let's say you need to construct an option 43 with http://phone.example.com as an option 66 and phonesettings.txt as option 67.
- Byte 1, option code 66,
0x42
- Byte 2, length of 24 bytes on
http://phone.example.com, so 0x18
- Bytes 3-26, the data.
0x687474703a2f2f70686f6e652e6578616d706c652e636f6d
- Byte 27, option code 67,
0x43
- Byte 28, length of 17 bytes on
phonesettings.txt, so 0x11
- Bytes 29-45, data.
0x70686f6e6573657474696e67732e747874
So, a complete config string of :
42:18:68:74:74:70:3a:2f:2f:70:68:6f:6e:65:2e:65:78:61:6d:70:6c:65:2e:63:6f:6d:43:11:70:68:6f:6e:65:73:65:74:74:69:6e:67:73:2e:74:78:74;
If that doesn't work, try adding the null bytes to the end of the data strings (and increase the length field accordingly) as in their example - they may either desire null bytes at the end of each option or an even number of bytes for each option's length. That's the downside of option 43 - they can do whatever they want!
Best Answer
Add an additional option of 43 / String / 01:04:00:00:00:02