simple filters question

[Ondrej Zajicek]

On Mon, Nov 11, 2013 at 10:08:30AM +0200, Sergey Popovich wrote:
> And yes, really according to documentation we could match only on set with 
> elements of same tyme.

That is true, IPs are matched against IP sets, while prefixes are matched
against prefix sets.  The main problem is that syntactic expression
'[ 192.168.1.0/24 ]' could be interpreted either as prefix set containing
one element, or as an shorthand for ip set containing 256 such addresses.

There is a way (although less convenient) how to write such ip sets even
in the current code: [ 192.168.1.0 .. 192.168.1.255 ].

> On the other hand, an ip type may be easily represented
> as prefix with length of max AFI prefix length (32 - IPv4, 128 - IPv6, so I
> see no problem using this conversion of ip to prefix type.

There is one major problem related to such change. The intuitive way
to write such expression is:

192.168.1.1 ~ [ 192.168.0.0/16 ]

In current code, user gets an error and notices that. After your patch,
user wouldn't get error, but the expression wouldn't work as expected 
(because it has to be '[ 192.168.0.0/16+ ]', which makes less sense).

I don't see a good solution for this problem, just several bad ones.
Perhaps to write a specialised match function for ip ~ pxset, which walks
the trie and returns true if any prefix matches.

> Moreover on IPv4 BIRD build there is implicit conversion of ip type to quad
> as on IPv4 they basically represent value with same format.

Which is a major PITA in the filter code.

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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