[PATCH] adding custom options in radv protocol, strict ipv6 regex

[Maria Matejka]

Hello!

This looks like a clever solution for such a problem. Thank you for the 
patch!

Regarding the bytestring syntax, what about adding some syntax like 
hex(deadbeef12345678) or even base64(...) where the user could write 
byte blob of any length?

Maria

On 6/12/23 13:08, Alexander Zubkov via Bird-users wrote:
> Hi,
>
> Currently one can use only a predefined set of advertised options in 
> radv protocol, that are supported by bird's configuration. It would be 
> convenient to be able to specify other possible options at least 
> manually as a blob so one should not wait until it is supported in the 
> code, released, etc.
>
> This idea is inspired by presentation by Ondřej Caletka at CSNOG, in 
> which he noticed the lack of either PREF64 option or possibility to 
> add custom options in various software.
>
> Attached patch [radv-custom.patch] makes it possible to define such 
> options with the syntax:
>
> other type <num> <bytestring>
>
> I can also prepare a patch for documentation if it is to be merged.
>
> But it does solve the question with PREF64 completely. Because 
> currently bytestring minimal length is 16 bytes, but for PREF64 we 
> need to provide a 14-byte blob. And for minimal RA option, it have to 
> be as short as 6 bytes.
>
> So another patch [bytestring-short.patch] allows bytestrings to be as 
> short as 6 bytes, when colon-notation is used: "01:02:03:04:05:06". 
> And I kept the minimum size of 16 bytes without colons, because it can 
> conflict with some symbol names.
>
> The main concern is that a 6-byte bytestring conflicts with the MAC 
> address representation. Bird does not have the type for it currently, 
> but who knows, it might need it in the future. So we might need some 
> new syntax for bytestring in that case. Or it can be postponed to 
> later time. In this case introduction of MAC-address lexems would 
> break configs that use 6-byte bytestrings (if we want to care much 
> about those).
>
> It is also not possible to define a 8-byte bytestring, because it 
> conflicts with IPv6 address, but we are introducing short bytestrings 
> for RA here, and 8-byte bytestrings are not strictly required for 
> that, because possible option sizes are 8, 16, ... with payloads 2 
> bytes less: 6, 14, ... So if one needs a 8-byte payload, he can easily 
> pad it with extra zeroes ":00" with the same on-the-wire result. But 
> still, this gives one more reason for an additional syntax for 
> bytestrings.
>
> There also was possbility to explicitly allow only 6, 7, 9 and greater 
> lengths of bytestrings. Or to move IPv6 regex definition before 
> bytestring definition to make it more preferrable. I choose the second 
> variant, but IPv6 regex is too loose now and match many things far 
> from IPv6 notation. So I decided to provide a more strict regex 
> definition for IPv6 addresses. Of course it is ugly, but I think it 
> could be helpful anyway, because it does not conflict with other 
> similar lexems, including MAC addresses.
>
> As a downside for this, in case of some typo in IPv6 address, there 
> will not be a meaningful error about bad IPv6 address. So I added an 
> additional regex there, to catch lexems with hex digits and at least 2 
> colons to show more meaningful error for that. But I'm not sure about it.
>
> If those changes for bytestrings are OK too, I also can prepare 
> further patch for documentation.
>
> Have a nice day,
> Alexander Zubkov

-- 
Maria Matejka | BIRD Team Leader | CZ.NIC, z.s.p.o.
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