mirror of
https://github.com/matrix-construct/construct
synced 2024-11-16 15:00:51 +01:00
114 lines
4.7 KiB
Text
114 lines
4.7 KiB
Text
The hostmask/netmask system.
|
|
Copyright(C) 2001 by Andrew Miller(A1kmm)<a1kmm@mware.virtualave.net>
|
|
|
|
Contents
|
|
========
|
|
* Section 1: Motivation
|
|
* Section 2: Underlying mechanism
|
|
- 2.1: General overview.
|
|
- 2.2: IPv4 netmasks.
|
|
- 2.3: IPv6 netmasks.
|
|
- 2.4: Hostmasks.
|
|
* Section 3: Exposed abstraction layer
|
|
- 3.1: Parsing masks.
|
|
- 3.2: Adding configuration items.
|
|
- 3.3: Initialising or rehashing.
|
|
- 3.4: Finding IP/host confs.
|
|
- 3.5: Deleting entries.
|
|
- 3.6: Reporting entries.
|
|
|
|
Section 1: Motivation
|
|
=====================
|
|
Looking up config hostnames and IP addresses(such as for I-lines and
|
|
K-lines) needs to be implemented efficiently. It turns out a hash
|
|
based algorithm like that employed here performs well on the average
|
|
case, which is what we should be the most concerned about. A profiling
|
|
comparison with the mtrie code using data from a real network confirmed
|
|
that this algorithm performs much better.
|
|
|
|
Section 2: Underlying mechanism
|
|
===============================
|
|
2.1: General overview
|
|
---------------------
|
|
In short, a hash-table with linked lists for buckets is used to locate
|
|
the correct hostname/netmask entries. In order to support CIDR IPs and
|
|
wildcard masks, the entire key cannot be hashed, and there is a need to
|
|
rehash. The means for deciding how much to hash differs between hostmasks
|
|
and IPv4/6 netmasks.
|
|
|
|
2.2: IPv4 netmasks
|
|
------------------
|
|
In order to hash IPv4 netmasks for addition to the hash, the mask is first
|
|
processed to a 32 bit address and a number of bits used. All unused bits
|
|
are set to 0. The mask could be in the forms:
|
|
1.2.3.4 => 1.2.3.4 32
|
|
1.2.3.* => 1.2.3.0 24
|
|
1.2 => 1.2.0.0 16
|
|
1.2.3.64/26 => 1.2.3.64 26
|
|
The number of whole bytes is then calculated, and only those bytes are
|
|
hashed. (e.g. 1.2.3.64/26 and 1.2.3.0/24 hash the same).
|
|
When a complete IPv4 address is given so that an IPv4 match can be found,
|
|
the entire IP address is first hashed, and looked up in the table. Then
|
|
the most significant three bytes are hashed, followed by the most
|
|
significant two, the most significant one, and finally the 'identity hash'
|
|
bucket is searched(to match masks like 192/7).
|
|
|
|
2.3: IPv6 netmasks
|
|
------------------
|
|
As per IPv4 netmasks, except that instead of rehashing with a one byte
|
|
granularity, a 16 bit(two byte) granularity is used, as 16 rehashes is
|
|
considered too great a fixed offset to be justified for a (possible)
|
|
slight reduction in hash collisions.
|
|
|
|
2.4: Hostmasks
|
|
--------------
|
|
On adding a hostmask to the hash, all of the hostmask right of the next
|
|
dot after the last wildcard character in the string is hashed, or in the
|
|
case that there are no wildcards in the hostmask, the entire string is
|
|
hashed.
|
|
On searching for a hostmask match, the entire hostname is hashed, followed
|
|
by the entire hostmask after the first dot, followed by the entire
|
|
hostmask after the second dot, and so on. Finally, the 'identity' hash
|
|
bucket is checked, to catch hostnames like *test*.
|
|
|
|
Section 3: Exposed abstraction layer
|
|
====================================
|
|
Section 3.1: Parsing masks
|
|
--------------------------
|
|
Call "parse_netmask()" with the netmask and a pointer to an irc_inaddr
|
|
structure to be filled in, as well as a pointer to an integer where the
|
|
number of bits will be placed.
|
|
Always check the return value. If it returns HM_HOST, it means that the
|
|
mask is probably a hostname mask. If it returns HM_IPV4, it means it was
|
|
an IPv4 address. If it returns HM_IPV6, it means it was an IPv6 address.
|
|
If parse_netmask returns HM_HOST, no change is made to the irc_inaddr
|
|
structure or the number of bits.
|
|
|
|
Section 3.2: Adding configuration items
|
|
---------------------------------------
|
|
Call "add_conf_by_address" with the hostname or IP mask, the username,
|
|
and the ConfItem* to associate with this mask.
|
|
|
|
Section 3.3: Initialising and rehashing
|
|
----------------------------------------
|
|
To initialise, call init_host_hash(). This only needs to be done once on
|
|
startup.
|
|
On rehash, to wipe out the old unwanted conf, and free them if there are
|
|
no references to them, call clear_out_address_conf().
|
|
|
|
Section 3.4: Finding IP/host confs
|
|
----------------------------------
|
|
Call find_address_conf() with the hostname, the username, the address,
|
|
and the address family.
|
|
To find a d-line, call find_dline() with the address and address family.
|
|
|
|
Section 3.5: Deletiing entries
|
|
------------------------------
|
|
Call delete_one_address_conf() with the hostname and the ConfItem*.
|
|
|
|
Section 3.6: Reporting entries
|
|
------------------------------
|
|
Call report_dlines, report_exemptlines, report_Klines() or report_Ilines()
|
|
with the client pointer to report to. Note these walk the hash, which is
|
|
inefficient, but these are not called often enough to justify the memory
|
|
and maintenance clockcycles to for more efficient data structure.
|