draft-dhankins-atomic-dhcp-00

David W. HankinsSoftware Engineer

Internet Systems Consortium, INC.

So you'd like to know how DHCP software process options

• Or if you don't, you should.

• At least, if you want your option used before new software can be written and deployed.

• Or if you want a better chance of getting your option out in software sooner rather than later.

Option Processing Req's

• Accept input from sysadmins/client-users to configure option contents.

• Translate this into in-memory db.• Translate this into wire format.• And back to in-memory on the far

end• Finally, to an output format.

For state keeping, applications, etc.

• Each option has its own format def.

One approach.

• There are probably many approaches, this one is ISC's.

• The in-memory format is wire format.• The output format is (nearly)

identical to the input format.• So you need 2 functions per each

option.

Enter 'Atomic' DHCP

• Unless you looked at all the similar option formats, and made a generic language to describe each option's format.

• This makes 'DHCP Format Atoms', which can be strung together in series to create 'DHCP Molecules'.

A day in the life of Ivan ...

• Configure• Transmit• Receive

Configuring Ivan's Format

• option space ivanspace;• option ivanspace.value code 1 = int32;• option ivanspace.name code 2 = text;• option ivanspace.subnets code 3 = array

of { ip-address, ip-address };• option ivanspace.domain code 4 =

domain-list compressed;• option vivso.ivan code XXX = encapsulate

ivanspace;

Configuring Ivan's Content

• option ivanspace.value 67;• option ivanspace.name

“Denisovitch”;• option ivanspace.subnets 10.0.0.0

255.255.255.0, 192.168.0.0 255.255.255.0;

• option ivanspace.domain “example.com”, “a\040name.example.com”;

Transmitting Ivan

• XXX 0x3B 0x01 0x04 0x00 0x00 0x00 0x43 0x02 0x0B D e n i s o v i t c h 0x03 0x10 0x0A 0x00 0x00 0x00 0xFF

0xFF 0xFF 0x00 0xC0 0xA8 0x00 0x00 0xFF 0xFF 0xFF 0x00

0x04 0x17 0x07 e x a m p l e 0x03 c o m 0x00 0x06 a 0x20 n a m e 0xC0 0x00

Receiving Ivan

• If the client doesn't have the option definition, it is treated as opaque data. option vivso.unknown-XXX

01:04:00:00:00:43:02:0B:44:65:6E:69:73:6F:76:69:64:63:68:03:10:0A:00:00:00:FF:FF:FF:00:C0:A8:00:00:FF:FF:FF:00;

• Otherwise, it is in the format specified by the format definitions.

Receiving Ivan, Cont'd.

• option ivanspace.value 67; export new_ivanspace_value=”67”

• option ivanspace.name “Denisovitch”; export

new_ivanspace_name=”Denisovitch”

• option ivanspace.subnets 10.0.0.0 255.255.255.0, 192.168.0.0 255.255.255.0; option new_ivanspace_subnets=”...

Domain names are Problem Children

• option ivanspace.domain “example.com”, “a name.example.com”; export

new_ivanspace_domain=”example.com a\032name.example.com”

• Note that the option is represented differently, using different escapes. DNS presentation syntax uses base 10. ISC DHCP escape syntax can quote

spaces and uses octal escapes.

To-Do

• 'Lessons Learned' section is mostly just an outline.

• 'Security' section is a placeholder.• Could use input from other implementors.

However other implementors want to participate.

• The code documented is not all 'running'.

Questions

• Is this a WG item?