sortlist usage

[Drunkard Zhang]

2012/6/19 Drunkard Zhang <gongfan193 at gmail.com>:
> I‘m working for a China ISP, with a very complex network arch. One of
> these complex things is the CDN of ICP returned a bunch of IP
> addresses, which distributed in geographically varies, and some IP
> addresses located way far from us. So I want do some "sortlist" which
> sorts the IP addresses by geographical distance, not considering
> latency and CDN peer's load now.
>
> From ARM 9.9, I get this example:
>
> sortlist {
> // IF the local host
> // THEN first fit on the following nets
> { localhost;
> { localnets;
> 192.168.1/24;
> { 192.168.2/24; 192.168.3/24; }; }; };
> // IF on class C 192.168.1 THEN use .1, or .2 or .3
> { 192.168.1/24;
> { 192.168.1/24;
> { 192.168.2/24; 192.168.3/24; }; }; };
> // IF on class C 192.168.2 THEN use .2, or .1 or .3
> { 192.168.2/24;
> { 192.168.2/24;
> { 192.168.1/24; 192.168.3/24; }; }; };
> // IF on class C 192.168.3 THEN use .3, or .1 or .2
> { 192.168.3/24;
> { 192.168.3/24;
> { 192.168.1/24; 192.168.2/24; }; }; };
> // IF .4 or .5 THEN prefer that net
> { { 192.168.4/24; 192.168.5/24; };
> };
> };
>
> Here's my understanding after some testing:
> 1st level of brace matches client's IP addresses;
> 2nd level of brace matches IP in rrset data;
> 3rd, what's this level used for? Is it just ordering behind 2nd? When
> I added 3rd level of address_match_list, the ordering of rrset just
> failed.
>
> By testing, I found that the 1st level of entry can only be one IP
> range or acl name, sort will fail while 1st level is more than one
> address_match_list. Is this intended or I missed something?
>
> BTW, is 4th or 5th or 6... level of address_match_list supported?
>
> Another thing related: can I use sortlist for determining which
> upstream DNS server to query?
>
> Here's one testing domain name I used:
> 11:11:21 ~ $ dig +short @220.115.251.73 s.kaixin001.com.cn
> s.kaixin001.com.cn.lxdns.com.
> s.kaixin001.z.lxdns.com.
> kx.xdwscache.glb0.lxdns.com.
> 124.14.10.17
> 124.14.10.25
> 124.14.10.18
> 121.251.53.95
> 58.22.135.38
>
> The first 3 IPs located locally, 121.251.53.95 located in Anhui, and
> 58.22.135.38 located in Fuzhou, Fujian. The first 3 IPs returned
> cyclicly, 4th and 5th IP are fixed.

I think there's some trick not mentioned in ARM, like:
* The 1st level of brace can only be ONE element, address_match_list.
bind won't deal with more than one address_match_list;
* You can define more than 2 level of braces, but only configurations
within 2 level actived, others are ignored;
* Misswrite of sortlist config can not be detected, it just failed;

So you can write anything you like with following format:
sortlist {
{ acl-client;
{ acl-client; acl-local-city; acl-local-province; acl-local-contry;
...other-acls;
}; };

configurations out of this frame won't work. Am I right?