By default, the bld daemon listens to requests on port 2905. Requests are either IP addresses submissions or checks against the black list.
bld uses a very simple algorithm to decide whether to add IP addresses to the blacklist or not. The first time an IP address is submitted, it is added to an internal list with a timestamp and all further requests increment a counter for this IP. As soon as the minimum time interval is elapsed (default: 30 seconds), and if a maximum requests ratio is reached (default: 10 submissions in the 30 seconds interval), the IP is put in the blacklist. It is then blacklisted for a configurable time (default: 900 seconds).
Requests sent to bld are rather simple. Each request or reply is followed by a linefeed and a carriage return. A client may only send one request per TCP session. As of now, two commands may be used: ip (address submission) and ip? (ask if address is blacklisted).
ip=a.b.c.d submits an IP address. The server acknowledges either with a 200 code if the address is not blacklisted or a 421 if it is.
ipdecr=a.b.c.d decrements the internal counter for an IP address. The lowest value for the counter is zero. The server always acknowledges with a 200 code.
ip?=a.b.c.d asks if address is blacklisted. The server reply may be 421 if it is or 200 if it's not.
ipbl=a.b.c.d forces the insertion in the blacklist. The server acknowledges with a 200 code.
If using IP based restrictions, the server reply may be 600 if the client is not in the correct ACL to perform a request. Any other error will generate a reply with a 500 error code.
bld binds to localhost by default and accepts any local request, so please make sure that only trusted users can establish a connection to the daemon. Please check that all authorized hosts meet the minimal security requirements before changing this parameter even if using an access control list (see bld_acl.conf(5)).
bld will log some statistics if it receives the SIGUSR1 signal. SIGUSR2 is used to force a dump of both lists in bld working directory.
/etc/bld/bld.conf /etc/bld/bld_acl.conf /etc/bld/bld_whitelist.conf /var/run/bld/bld.pid /var/run/bld/bld_iplist.dump /var/run/bld/bld_blacklist.dump
bld.conf(5) bld_acl.conf(5) bld_whitelist.conf(5) bldread(8) bldquery(8) bldsubmit(8) blddecr(8)