<s>
Internet	B-Protocol
Relay	I-Protocol
Chat	I-Protocol
(	O
IRC	B-Protocol
)	O
is	O
a	O
text-based	B-Application
chat	O
system	O
for	O
instant	B-Application
messaging	I-Application
.	O
</s>
<s>
IRC	B-Protocol
is	O
designed	O
for	O
group	B-Architecture
communication	I-Architecture
in	O
discussion	O
forums	O
,	O
called	O
channels	O
,	O
but	O
also	O
allows	O
one-on-one	O
communication	O
via	O
private	B-Application
messages	I-Application
as	O
well	O
as	O
chat	O
and	O
data	O
transfer	O
,	O
including	O
file	O
sharing	O
.	O
</s>
<s>
Internet	B-Protocol
Relay	I-Protocol
Chat	I-Protocol
is	O
implemented	O
as	O
an	O
application	B-Application
layer	I-Application
protocol	O
to	O
facilitate	O
communication	O
in	O
the	O
form	O
of	O
text	O
.	O
</s>
<s>
The	O
chat	O
process	O
works	O
on	O
a	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
networking	I-Operating_System
model	I-Operating_System
.	O
</s>
<s>
Users	O
connect	O
,	O
using	O
a	O
clientwhich	O
may	O
be	O
a	O
web	B-Application
app	I-Application
,	O
a	O
standalone	B-Application
desktop	I-Application
program	I-Application
,	O
or	O
embedded	O
into	O
part	O
of	O
a	O
larger	O
programto	O
an	O
IRC	B-Protocol
server	B-Application
,	O
which	O
may	O
be	O
part	O
of	O
a	O
larger	O
IRC	B-Protocol
network	I-Protocol
.	O
</s>
<s>
Examples	O
of	O
programs	O
used	O
to	O
connect	O
include	O
Mibbit	O
,	O
IRCCloud	O
,	O
KiwiIRC	O
,	O
and	O
mIRC	B-Language
.	O
</s>
<s>
IRC	B-Protocol
usage	O
has	O
been	O
declining	O
steadily	O
since	O
2003	O
,	O
losing	O
60	O
percent	O
of	O
its	O
users	O
.	O
</s>
<s>
In	O
April	O
2011	O
,	O
the	O
top	O
100	O
IRC	B-Protocol
networks	I-Protocol
served	O
more	O
than	O
half	O
a	O
million	O
users	O
at	O
a	O
time	O
.	O
</s>
<s>
IRC	B-Protocol
was	O
created	O
by	O
Jarkko	O
Oikarinen	O
in	O
August	O
1988	O
to	O
replace	O
a	O
program	O
called	O
MUT	O
(	O
MultiUser	O
Talk	O
)	O
on	O
a	O
BBS	B-Application
called	O
OuluBox	O
at	O
the	O
University	O
of	O
Oulu	O
in	O
Finland	O
,	O
where	O
he	O
was	O
working	O
at	O
the	O
Department	O
of	O
Information	O
Processing	O
Science	O
.	O
</s>
<s>
Jarkko	O
intended	O
to	O
extend	O
the	O
BBS	B-Application
software	O
he	O
administered	O
,	O
to	O
allow	O
news	O
in	O
the	O
Usenet	B-Application
style	O
,	O
real	O
time	O
discussions	O
and	O
similar	O
BBS	B-Application
features	O
.	O
</s>
<s>
The	O
first	O
IRC	B-Protocol
network	I-Protocol
was	O
running	O
on	O
a	O
single	O
server	B-Application
named	O
tolsun.oulu.fi	O
.	O
</s>
<s>
Oikarinen	O
found	O
inspiration	O
in	O
a	O
chat	O
system	O
known	O
as	O
Bitnet	B-Protocol
Relay	I-Protocol
,	O
which	O
operated	O
on	O
the	O
BITNET	B-General_Concept
.	O
</s>
<s>
Jyrki	O
Kuoppala	O
pushed	O
Oikarinen	O
to	O
ask	O
Oulu	O
University	O
to	O
free	O
the	O
IRC	B-Protocol
code	O
so	O
that	O
it	O
also	O
could	O
be	O
run	O
outside	O
of	O
Oulu	O
,	O
and	O
after	O
they	O
finally	O
got	O
it	O
released	O
,	O
Jyrki	O
Kuoppala	O
immediately	O
installed	O
another	O
server	B-Application
.	O
</s>
<s>
This	O
was	O
the	O
first	O
"	O
IRC	B-Protocol
network	I-Protocol
"	O
.	O
</s>
<s>
Oikarinen	O
got	O
some	O
friends	O
at	O
the	O
Helsinki	O
University	O
and	O
Tampere	O
University	O
to	O
start	O
running	O
IRC	B-Protocol
servers	O
when	O
his	O
number	O
of	O
users	O
increased	O
and	O
other	O
universities	O
soon	O
followed	O
.	O
</s>
<s>
At	O
this	O
time	O
Oikarinen	O
realized	O
that	O
the	O
rest	O
of	O
the	O
BBS	B-Application
features	O
probably	O
would	O
n't	O
fit	O
in	O
his	O
program	O
.	O
</s>
<s>
They	O
had	O
their	O
own	O
IRC	B-Protocol
network	I-Protocol
running	O
and	O
wanted	O
to	O
connect	O
to	O
the	O
Finnish	O
network	O
.	O
</s>
<s>
They	O
had	O
obtained	O
the	O
program	O
from	O
one	O
of	O
Oikarinen	O
's	O
friends	O
,	O
Vijay	O
Subramaniam	O
—	O
the	O
first	O
non-Finnish	O
person	O
to	O
use	O
IRC	B-Protocol
.	O
</s>
<s>
IRC	B-Protocol
then	O
grew	O
larger	O
and	O
got	O
used	O
on	O
the	O
entire	O
Finnish	O
national	O
network	O
—	O
FUNET	O
—	O
and	O
then	O
connected	O
to	O
Nordunet	O
,	O
the	O
Scandinavian	O
branch	O
of	O
the	O
Internet	O
.	O
</s>
<s>
In	O
November	O
1988	O
,	O
IRC	B-Protocol
had	O
spread	O
across	O
the	O
Internet	O
and	O
in	O
the	O
middle	O
of	O
1989	O
,	O
there	O
were	O
some	O
40	O
servers	O
worldwide	O
.	O
</s>
<s>
In	O
August	O
1990	O
,	O
the	O
first	O
major	O
disagreement	O
took	O
place	O
in	O
the	O
IRC	B-Protocol
world	O
.	O
</s>
<s>
The	O
"	O
A-net	O
"	O
(	O
Anarchy	O
net	O
)	O
included	O
a	O
server	B-Application
named	O
eris.berkeley.edu	O
.	O
</s>
<s>
As	O
Greg	O
"	O
wumpus	O
"	O
Lindahl	O
explains	O
:	O
"	O
it	O
had	O
a	O
wildcard	O
server	B-Application
line	O
,	O
so	O
people	O
were	O
hooking	O
up	O
servers	O
and	O
nick-colliding	O
everyone	O
"	O
.	O
</s>
<s>
The	O
"	O
Eris	O
Free	O
Network	O
"	O
,	O
EFnet	O
,	O
made	O
the	O
eris	O
machine	O
the	O
first	O
to	O
be	O
Q-lined	O
(	O
Q	O
for	O
quarantine	O
)	O
from	O
IRC	B-Protocol
.	O
</s>
<s>
Once	O
A-net	O
disbanded	O
,	O
the	O
name	O
EFnet	O
became	O
meaningless	O
,	O
and	O
once	O
again	O
it	O
was	O
the	O
one	O
and	O
only	O
IRC	B-Protocol
network	I-Protocol
.	O
</s>
<s>
Around	O
that	O
time	O
IRC	B-Protocol
was	O
used	O
to	O
report	O
on	O
the	O
1991	O
Soviet	O
coup	O
d'état	O
attempt	O
throughout	O
a	O
media	O
blackout	O
.	O
</s>
<s>
It	O
was	O
previously	O
used	O
in	O
a	O
similar	O
fashion	O
during	O
the	O
Gulf	B-Application
War	I-Application
.	O
</s>
<s>
Chat	B-Protocol
logs	I-Protocol
of	O
these	O
and	O
other	O
events	O
are	O
kept	O
in	O
the	O
ibiblio	O
archive	O
.	O
</s>
<s>
The	O
"	O
undernetters	O
"	O
wanted	O
to	O
take	O
ircd	O
further	O
in	O
an	O
attempt	O
to	O
make	O
it	O
use	O
less	O
bandwidth	O
and	O
to	O
try	O
to	O
sort	O
out	O
the	O
channel	O
chaos	O
(	O
netsplits	B-Error_Name
and	O
takeovers	O
)	O
that	O
EFnet	O
started	O
to	O
suffer	O
from	O
.	O
</s>
<s>
The	O
first	O
server	B-Application
list	O
presented	O
,	O
from	O
15	O
February	O
1993	O
,	O
includes	O
servers	O
from	O
the	O
U.S.	O
,	O
Canada	O
,	O
France	O
,	O
Croatia	O
and	O
Japan	O
.	O
</s>
<s>
In	O
May	O
1993	O
,	O
RFC	O
1459	O
was	O
published	O
and	O
details	O
a	O
simple	O
protocol	O
for	O
client/server	B-Operating_System
operation	O
,	O
channels	O
,	O
one-to-one	O
and	O
one-to-many	O
conversations	O
.	O
</s>
<s>
It	O
is	O
notable	O
that	O
a	O
significant	O
number	O
of	O
extensions	O
like	O
CTCP	O
,	O
colors	O
and	O
formats	O
are	O
not	O
included	O
in	O
the	O
protocol	O
specifications	O
,	O
nor	O
is	O
character	B-General_Concept
encoding	I-General_Concept
,	O
which	O
led	O
various	O
implementations	O
of	O
servers	O
and	O
clients	O
to	O
diverge	O
.	O
</s>
<s>
DALnet	O
was	O
thus	O
based	O
on	O
the	O
Undernet	O
ircd	O
server	B-Application
,	O
although	O
the	O
DALnet	O
pioneers	O
were	O
EFnet	O
abandoners	O
.	O
</s>
<s>
)	O
,	O
global	O
K:Lines	O
(	O
ban	O
of	O
one	O
person	O
or	O
an	O
entire	O
domain	O
from	O
a	O
server	B-Application
or	O
the	O
entire	O
network	O
)	O
,	O
IRCop	O
only	O
communications	O
:	O
GlobOps	O
,	O
+H	O
mode	O
showing	O
that	O
an	O
IRCop	O
is	O
a	O
"	O
helpop	O
"	O
etc	O
.	O
</s>
<s>
This	O
event	O
is	O
also	O
known	O
as	O
"	O
The	O
Great	O
Split	O
"	O
in	O
many	O
IRC	B-Protocol
societies	O
.	O
</s>
<s>
IRC	B-Protocol
has	O
changed	O
much	O
over	O
its	O
life	O
on	O
the	O
Internet	O
.	O
</s>
<s>
New	O
server	B-Application
software	I-Application
has	O
added	O
a	O
multitude	O
of	O
new	O
features	O
.	O
</s>
<s>
Extra	O
modes	O
:	O
While	O
the	O
original	O
IRC	B-Protocol
system	O
used	O
a	O
set	O
of	O
standard	O
user	O
and	O
channel	O
modes	O
,	O
new	O
servers	O
add	O
many	O
new	O
modes	O
for	O
features	O
such	O
as	O
removing	O
color	O
codes	O
from	O
text	O
,	O
or	O
obscuring	O
a	O
user	O
's	O
hostmask	O
(	O
"	O
cloaking	O
"	O
)	O
to	O
protect	O
from	O
denial-of-service	O
attacks	O
.	O
</s>
<s>
Proxy	B-Application
detection	O
:	O
Most	O
modern	O
servers	O
support	O
detection	O
of	O
users	O
attempting	O
to	O
connect	O
through	O
an	O
insecure	O
(	O
misconfigured	O
or	O
exploited	O
)	O
proxy	B-Application
server	I-Application
,	O
which	O
can	O
then	O
be	O
denied	O
a	O
connection	O
.	O
</s>
<s>
This	O
proxy	B-Application
detection	O
software	O
is	O
used	O
by	O
several	O
networks	O
,	O
although	O
that	O
real	O
time	O
list	O
of	O
proxies	O
is	O
defunct	O
since	O
early	O
2006	O
.	O
</s>
<s>
Encryption	O
:	O
For	O
the	O
client-to-server	O
leg	O
of	O
the	O
connection	O
TLS	B-Protocol
might	O
be	O
used	O
(	O
messages	O
cease	O
to	O
be	O
secure	O
once	O
they	O
are	O
relayed	O
to	O
other	O
users	O
on	O
standard	O
connections	O
,	O
but	O
it	O
makes	O
eavesdropping	O
on	O
or	O
wiretapping	O
an	O
individual	O
's	O
IRC	B-Protocol
sessions	O
difficult	O
)	O
.	O
</s>
<s>
For	O
client-to-client	O
communication	O
,	O
SDCC	O
(	O
Secure	O
DCC	O
)	O
can	O
be	O
used	O
.	O
</s>
<s>
Connection	O
protocol	O
:	O
IRC	B-Protocol
can	O
be	O
connected	O
to	O
via	O
IPv4	B-Protocol
,	O
the	O
old	O
version	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
or	O
by	O
IPv6	B-Protocol
,	O
the	O
current	O
standard	O
of	O
the	O
protocol	O
.	O
</s>
<s>
,	O
a	O
new	O
standardization	O
effort	O
is	O
under	O
way	O
under	O
a	O
working	O
group	O
called	O
IRCv3	B-Protocol
,	O
which	O
focuses	O
on	O
more	O
advanced	O
client	B-Protocol
features	O
like	O
instant	O
notifications	O
,	O
better	O
history	O
support	O
and	O
improved	O
security	O
.	O
</s>
<s>
,	O
no	O
major	O
IRC	B-Protocol
networks	I-Protocol
have	O
fully	O
adopted	O
the	O
proposed	O
standard	O
.	O
</s>
<s>
there	O
are	O
481	O
different	O
IRC	B-Protocol
networks	I-Protocol
known	O
to	O
be	O
operating	O
,	O
of	O
which	O
the	O
open	O
source	O
Libera	O
Chat	O
,	O
founded	O
in	O
May	O
2021	O
,	O
has	O
the	O
most	O
users	O
,	O
with	O
20,374	O
channels	O
on	O
26	O
servers	O
;	O
between	O
them	O
,	O
the	O
top	O
100	O
IRC	B-Protocol
networks	I-Protocol
share	O
over	O
100	O
thousand	O
channels	O
operating	O
on	O
about	O
one	O
thousand	O
servers	O
.	O
</s>
<s>
After	O
its	O
golden	O
era	O
during	O
the	O
1990s	O
and	O
early	O
2000s	O
(	O
240,000	O
users	O
on	O
QuakeNet	O
in	O
2004	O
)	O
,	O
IRC	B-Protocol
has	O
seen	O
a	O
significant	O
decline	O
,	O
losing	O
around	O
60%	O
of	O
users	O
between	O
2003	O
and	O
2012	O
,	O
with	O
users	O
moving	O
to	O
newer	O
social	O
media	O
platforms	O
like	O
Facebook	B-Application
or	O
Twitter	B-Application
,	O
but	O
also	O
to	O
open	O
platforms	O
like	O
XMPP	B-Protocol
which	O
was	O
developed	O
in	O
1999	O
.	O
</s>
<s>
The	O
largest	O
IRC	B-Protocol
networks	I-Protocol
have	O
traditionally	O
been	O
grouped	O
as	O
the	O
"	O
Big	O
Four	O
"	O
—	O
a	O
designation	O
for	O
networks	O
that	O
top	O
the	O
statistics	O
.	O
</s>
<s>
The	O
Big	O
Four	O
networks	O
change	O
periodically	O
,	O
but	O
due	O
to	O
the	O
community	O
nature	O
of	O
IRC	B-Protocol
there	O
are	O
a	O
large	O
number	O
of	O
other	O
networks	O
for	O
users	O
to	O
choose	O
from	O
.	O
</s>
<s>
IRC	B-Protocol
reached	O
6	O
million	O
simultaneous	O
users	O
in	O
2001	O
and	O
10	O
million	O
users	O
in	O
2004-2005	O
,	O
dropping	O
to	O
around	O
350k	O
in	O
2021	O
.	O
</s>
<s>
,	O
the	O
top10	O
IRC	B-Protocol
networks	I-Protocol
are	O
:	O
</s>
<s>
The	O
top	O
100	O
IRC	B-Protocol
networks	I-Protocol
have	O
around	O
230k	O
users	O
connected	O
at	O
peak	O
hours	O
.	O
</s>
<s>
IRC	B-Protocol
is	O
an	O
open	O
protocol	O
that	O
uses	O
TCP	B-Protocol
and	O
,	O
optionally	O
,	O
TLS	B-Protocol
.	O
</s>
<s>
An	O
IRC	B-Protocol
server	B-Application
can	O
connect	O
to	O
other	O
IRC	B-Protocol
servers	O
to	O
expand	O
the	O
IRC	B-Protocol
network	I-Protocol
.	O
</s>
<s>
Users	O
access	O
IRC	B-Protocol
networks	I-Protocol
by	O
connecting	O
a	O
client	B-Protocol
to	O
a	O
server	B-Application
.	O
</s>
<s>
There	O
are	O
many	O
client	B-Protocol
implementations	O
,	O
such	O
as	O
mIRC	B-Language
,	O
HexChat	B-Protocol
and	O
irssi	B-Protocol
,	O
and	O
server	B-Application
implementations	O
,	O
e.g.	O
</s>
<s>
Most	O
IRC	B-Protocol
servers	O
do	O
not	O
require	O
users	O
to	O
register	O
an	O
account	O
but	O
a	O
nickname	O
is	O
required	O
before	O
being	O
connected	O
.	O
</s>
<s>
IRC	B-Protocol
was	O
originally	O
a	O
plain	O
text	O
protocol	O
(	O
although	O
later	O
extended	O
)	O
,	O
which	O
on	O
request	O
was	O
assigned	O
port	O
194/TCP	O
by	O
IANA	O
.	O
</s>
<s>
However	O
,	O
the	O
de	O
facto	O
standard	O
has	O
always	O
been	O
to	O
run	O
IRC	B-Protocol
on	O
6667/TCP	O
and	O
nearby	O
port	O
numbers	O
(	O
for	O
example	O
TCP	B-Protocol
ports	I-Protocol
6660	O
–	O
6669	O
,	O
7000	O
)	O
to	O
avoid	O
having	O
to	O
run	O
the	O
IRCd	O
software	O
with	O
root	B-Application
privileges	I-Application
.	O
</s>
<s>
The	O
protocol	O
specified	O
that	O
characters	O
were	O
8-bit	O
but	O
did	O
not	O
specify	O
the	O
character	B-General_Concept
encoding	I-General_Concept
the	O
text	O
was	O
supposed	O
to	O
use	O
.	O
</s>
<s>
All	O
client-to-server	O
IRC	B-Protocol
protocols	O
in	O
use	O
today	O
are	O
descended	O
from	O
the	O
protocol	O
implemented	O
in	O
the	O
irc2.4.0	O
version	O
of	O
the	O
IRC2	O
server	B-Application
,	O
and	O
documented	O
in	O
RFC	O
1459	O
.	O
</s>
<s>
Although	O
many	O
specifications	O
on	O
the	O
IRC	B-Protocol
protocol	O
have	O
been	O
published	O
,	O
there	O
is	O
no	O
official	O
specification	O
,	O
as	O
the	O
protocol	O
remains	O
dynamic	O
.	O
</s>
<s>
Microsoft	O
made	O
an	O
extension	O
for	O
IRC	B-Protocol
in	O
1998	O
via	O
the	O
proprietary	O
IRCX	O
.	O
</s>
<s>
They	O
later	O
stopped	O
distributing	O
software	O
supporting	O
IRCX	O
,	O
instead	O
developing	O
the	O
proprietary	O
MSNP	B-General_Concept
.	O
</s>
<s>
The	O
standard	O
structure	O
of	O
a	O
network	O
of	O
IRC	B-Protocol
servers	O
is	O
a	O
tree	B-Data_Structure
.	O
</s>
<s>
Messages	O
are	O
routed	O
along	O
only	O
necessary	O
branches	O
of	O
the	O
tree	B-Data_Structure
but	O
network	O
state	O
is	O
sent	O
to	O
every	O
server	B-Application
and	O
there	O
is	O
generally	O
a	O
high	O
degree	O
of	O
implicit	O
trust	O
between	O
servers	O
.	O
</s>
<s>
A	O
misbehaving	O
or	O
malicious	O
server	B-Application
can	O
cause	O
major	O
damage	O
to	O
the	O
network	O
and	O
any	O
changes	O
in	O
structure	O
,	O
whether	O
intentional	O
or	O
a	O
result	O
of	O
conditions	O
on	O
the	O
underlying	O
network	O
,	O
require	O
a	O
net-split	O
and	O
net-join	O
.	O
</s>
<s>
Adding	O
a	O
server	B-Application
to	O
a	O
large	O
network	O
means	O
a	O
large	O
background	O
bandwidth	O
load	O
on	O
the	O
network	O
and	O
a	O
large	O
memory	O
load	O
on	O
the	O
server	B-Application
.	O
</s>
<s>
This	O
is	O
a	O
strength	O
in	O
comparison	O
to	O
non-multicasting	O
protocols	O
such	O
as	O
Simple	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
SMTP	B-Protocol
)	O
or	O
Extensible	B-Protocol
Messaging	I-Protocol
and	I-Protocol
Presence	I-Protocol
Protocol	I-Protocol
(	O
XMPP	B-Protocol
)	O
.	O
</s>
<s>
An	O
IRC	B-Protocol
daemon	B-Operating_System
can	O
also	O
be	O
used	O
on	O
a	O
local	O
area	O
network	O
(	O
LAN	O
)	O
.	O
</s>
<s>
IRC	B-Protocol
can	O
thus	O
be	O
used	O
to	O
facilitate	O
communication	O
between	O
people	O
within	O
the	O
local	O
area	O
network	O
(	O
internal	O
communication	O
)	O
.	O
</s>
<s>
IRC	B-Protocol
has	O
a	O
line-based	O
structure	O
.	O
</s>
<s>
Clients	O
send	O
single-line	O
messages	O
to	O
the	O
server	B-Application
,	O
receive	O
replies	O
to	O
those	O
messages	O
and	O
receive	O
copies	O
of	O
some	O
messages	O
sent	O
by	O
other	O
clients	O
.	O
</s>
<s>
Depending	O
on	O
the	O
command	O
,	O
these	O
may	O
either	O
be	O
handled	O
entirely	O
by	O
the	O
client	B-Protocol
,	O
or	O
(	O
generally	O
for	O
commands	O
the	O
client	B-Protocol
does	O
not	O
recognize	O
)	O
passed	O
directly	O
to	O
the	O
server	B-Application
,	O
possibly	O
with	O
some	O
modification	O
.	O
</s>
<s>
The	O
basic	O
means	O
of	O
communicating	O
to	O
a	O
group	O
of	O
users	O
in	O
an	O
established	O
IRC	B-Protocol
session	O
is	O
through	O
a	O
channel	O
.	O
</s>
<s>
Channels	O
on	O
a	O
network	O
can	O
be	O
displayed	O
using	O
the	O
IRC	B-Protocol
command	O
LIST	O
,	O
which	O
lists	O
all	O
currently	O
available	O
channels	O
that	O
do	O
not	O
have	O
the	O
modes	O
+s	O
or	O
+p	O
set	O
,	O
on	O
that	O
particular	O
network	O
.	O
</s>
<s>
Channels	O
that	O
are	O
available	O
across	O
an	O
entire	O
IRC	B-Protocol
network	I-Protocol
are	O
prefixed	O
with	O
a	O
'	O
#	O
 '	O
,	O
while	O
those	O
local	O
to	O
a	O
server	B-Application
use	O
'	O
&	O
 '	O
.	O
</s>
<s>
Modes	O
that	O
apply	O
to	O
users	O
on	O
a	O
channel	O
have	O
an	O
associated	O
symbol	O
that	O
is	O
used	O
to	O
represent	O
the	O
mode	O
in	O
names	O
replies	O
(	O
sent	O
to	O
clients	O
on	O
first	O
joining	O
a	O
channel	O
and	O
use	O
of	O
the	O
names	O
command	O
)	O
and	O
in	O
many	O
clients	O
also	O
used	O
to	O
represent	O
it	O
in	O
the	O
client	B-Protocol
's	O
displayed	O
list	O
of	O
users	O
in	O
a	O
channel	O
or	O
to	O
display	O
an	O
own	O
indicator	O
for	O
a	O
user	O
's	O
modes	O
.	O
</s>
<s>
In	O
order	O
to	O
correctly	O
parse	O
incoming	O
mode	O
messages	O
and	O
track	O
channel	O
state	O
the	O
client	B-Protocol
must	O
know	O
which	O
mode	O
is	O
of	O
which	O
type	O
and	O
for	O
the	O
modes	O
that	O
apply	O
to	O
a	O
user	O
on	O
a	O
channel	O
which	O
symbol	O
goes	O
with	O
which	O
letter	O
.	O
</s>
<s>
In	O
early	O
implementations	O
of	O
IRC	B-Protocol
this	O
had	O
to	O
be	O
hard-coded	O
in	O
the	O
client	B-Protocol
but	O
there	O
is	O
now	O
a	O
de	O
facto	O
standard	O
extension	O
to	O
the	O
protocol	O
called	O
ISUPPORT	O
that	O
sends	O
this	O
information	O
to	O
the	O
client	B-Protocol
at	O
connect	O
time	O
using	O
numeric	O
005	O
.	O
</s>
<s>
There	O
is	O
a	O
small	O
design	O
fault	O
in	O
IRC	B-Protocol
regarding	O
modes	O
that	O
apply	O
to	O
users	O
on	O
channels	O
:	O
the	O
names	O
message	O
used	O
to	O
establish	O
initial	O
channel	O
state	O
can	O
only	O
send	O
one	O
such	O
mode	O
per	O
user	O
on	O
the	O
channel	O
,	O
but	O
multiple	O
such	O
modes	O
can	O
be	O
set	O
on	O
a	O
single	O
user	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
user	O
holds	O
both	O
operator	O
status	O
( +o	O
)	O
and	O
voice	O
status	O
( +v	O
)	O
on	O
a	O
channel	O
,	O
a	O
new	O
client	B-Protocol
will	O
be	O
unable	O
to	O
see	O
the	O
mode	O
with	O
less	O
priority	O
(	O
i.e.	O
</s>
<s>
Workarounds	O
for	O
this	O
are	O
possible	O
on	O
both	O
the	O
client	B-Protocol
and	O
server	B-Application
side	O
but	O
none	O
are	O
widely	O
implemented	O
.	O
</s>
<s>
Many	O
daemons	B-Operating_System
and	O
networks	O
have	O
added	O
extra	O
modes	O
or	O
modified	O
the	O
behavior	O
of	O
modes	O
in	O
the	O
above	O
list	O
.	O
</s>
<s>
A	O
channel	O
operator	O
is	O
a	O
client	B-Protocol
on	O
an	O
IRC	B-Protocol
channel	O
that	O
manages	O
the	O
channel	O
.	O
</s>
<s>
IRC	B-Protocol
channel	I-Protocol
operators	I-Protocol
can	O
be	O
easily	O
seen	O
by	O
the	O
a	O
symbol	O
or	O
icon	O
next	O
to	O
their	O
name	O
(	O
varies	O
by	O
client	B-Protocol
implementation	O
,	O
commonly	O
a	O
"	O
@	O
"	O
symbol	O
prefix	O
,	O
a	O
green	O
circle	O
,	O
or	O
a	O
Latin	O
letter	O
"	O
+o	O
"	O
/	O
"	O
o	O
"	O
)	O
.	O
</s>
<s>
Give	O
another	O
user	O
IRC	B-Protocol
Channel	I-Protocol
Operator	I-Protocol
Status	O
or	O
IRC	B-Protocol
Channel	O
Voice	O
Status	O
.	O
</s>
<s>
Change	O
the	O
IRC	B-Protocol
Channel	O
topic	O
while	O
channel	O
mode	O
+t	O
is	O
set	O
.	O
</s>
<s>
Change	O
the	O
IRC	B-Protocol
Channel	O
Mode	O
locks	O
.	O
</s>
<s>
There	O
are	O
also	O
users	O
who	O
maintain	O
elevated	O
rights	O
on	O
their	O
local	O
server	B-Application
,	O
or	O
the	O
entire	O
network	O
;	O
these	O
are	O
called	O
IRC	B-Protocol
operators	O
,	O
sometimes	O
shortened	O
to	O
IRCops	O
or	O
Opers	O
(	O
not	O
to	O
be	O
confused	O
with	O
channel	O
operators	O
)	O
.	O
</s>
<s>
As	O
the	O
implementation	O
of	O
the	O
IRCd	O
varies	O
,	O
so	O
do	O
the	O
privileges	O
of	O
the	O
IRC	B-Protocol
operator	O
on	O
the	O
given	O
IRCd	O
.	O
</s>
<s>
RFC	O
1459	O
claims	O
that	O
IRC	B-Protocol
operators	O
are	O
"	O
a	O
necessary	O
evil	O
"	O
to	O
keep	O
a	O
clean	O
state	O
of	O
the	O
network	O
,	O
and	O
as	O
such	O
they	O
need	O
to	O
be	O
able	O
to	O
disconnect	O
and	O
reconnect	O
servers	O
.	O
</s>
<s>
Additionally	O
,	O
to	O
prevent	O
malicious	O
users	O
or	O
even	O
harmful	O
automated	O
programs	O
from	O
entering	O
IRC	B-Protocol
,	O
IRC	B-Protocol
operators	O
are	O
usually	O
allowed	O
to	O
disconnect	O
clients	O
and	O
completely	O
ban	O
IP	B-Protocol
addresses	I-Protocol
or	O
complete	O
subnets	O
.	O
</s>
<s>
usually	O
allow	O
their	O
IRC	B-Protocol
operators	O
also	O
to	O
handle	O
basic	O
"	O
ownership	O
"	O
matters	O
.	O
</s>
<s>
A	O
hostmask	O
is	O
a	O
unique	O
identifier	O
of	O
an	O
IRC	B-Protocol
client	B-Protocol
connected	O
to	O
an	O
IRC	B-Protocol
server	B-Application
.	O
</s>
<s>
IRC	B-Protocol
servers	O
,	O
services	O
,	O
and	O
other	O
clients	O
,	O
including	O
bots	O
,	O
can	O
use	O
it	O
to	O
identify	O
a	O
specific	O
IRC	B-Protocol
session	O
.	O
</s>
<s>
The	O
user	O
part	O
is	O
the	O
username	O
reported	O
by	O
ident	O
on	O
the	O
client	B-Protocol
.	O
</s>
<s>
If	O
ident	O
is	O
not	O
available	O
on	O
the	O
client	B-Protocol
,	O
the	O
username	O
specified	O
when	O
the	O
client	B-Protocol
connected	O
is	O
used	O
after	O
being	O
prefixed	O
with	O
a	O
tilde	O
.	O
</s>
<s>
The	O
host	O
part	O
is	O
the	O
hostname	B-Protocol
the	O
client	B-Protocol
is	O
connecting	O
from	O
.	O
</s>
<s>
If	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
client	B-Protocol
cannot	O
be	O
resolved	O
to	O
a	O
valid	O
hostname	B-Protocol
by	O
the	O
server	B-Application
,	O
it	O
is	O
used	O
instead	O
of	O
the	O
hostname	B-Protocol
.	O
</s>
<s>
Because	O
of	O
the	O
privacy	O
implications	O
of	O
exposing	O
the	O
IP	B-Protocol
address	I-Protocol
or	O
hostname	B-Protocol
of	O
a	O
client	B-Protocol
,	O
some	O
IRC	B-Protocol
daemons	B-Operating_System
also	O
provide	O
privacy	O
features	O
,	O
such	O
as	O
InspIRCd	O
or	O
UnrealIRCd	O
's	O
"	O
+x	O
"	O
mode	O
.	O
</s>
<s>
This	O
hashes	B-Algorithm
a	O
client	B-Protocol
IP	B-Protocol
address	I-Protocol
or	O
masks	O
part	O
of	O
a	O
client	B-Protocol
's	O
hostname	B-Protocol
,	O
making	O
it	O
unreadable	O
to	O
users	O
other	O
than	O
IRCops	O
.	O
</s>
<s>
Users	O
may	O
also	O
have	O
the	O
option	O
of	O
requesting	O
a	O
"	O
virtual	O
host	O
"	O
(	O
or	O
"	O
vhost	B-Protocol
"	O
)	O
,	O
to	O
be	O
displayed	O
in	O
the	O
hostmask	O
to	O
allow	O
further	O
anonymity	O
.	O
</s>
<s>
Some	O
IRC	B-Protocol
networks	I-Protocol
,	O
such	O
as	O
Libera	O
Chat	O
or	O
Freenode	O
,	O
use	O
these	O
as	O
"	O
cloaks	O
"	O
to	O
indicate	O
that	O
a	O
user	O
is	O
affiliated	O
with	O
a	O
group	O
or	O
project	O
.	O
</s>
<s>
There	O
are	O
three	O
provisional	O
recognized	O
uniform	B-Protocol
resource	I-Protocol
identifier	I-Protocol
(	O
URI	B-Protocol
)	O
schemes	O
for	O
Internet	B-Protocol
Relay	I-Protocol
Chat	I-Protocol
:	O
irc	B-Protocol
,	O
ircs	B-Protocol
,	O
and	O
irc6	O
.	O
</s>
<s>
(	O
where	O
items	O
enclosed	O
within	O
brackets	O
( [	O
,	O
]	O
)	O
are	O
optional	O
)	O
to	O
be	O
used	O
to	O
(	O
if	O
necessary	O
)	O
connect	O
to	O
the	O
specified	O
host	O
(	O
or	O
network	O
,	O
if	O
known	O
to	O
the	O
IRC	B-Protocol
client	B-Protocol
)	O
and	O
join	O
the	O
specified	O
channel	O
.	O
</s>
<s>
(	O
This	O
can	O
be	O
used	O
within	O
the	O
client	B-Protocol
itself	O
,	O
or	O
from	O
another	O
application	O
such	O
as	O
a	O
Web	B-Application
browser	I-Application
)	O
.	O
</s>
<s>
irc	B-Protocol
is	O
the	O
default	O
URI	B-Protocol
,	O
irc6	O
specifies	O
a	O
connection	O
to	O
be	O
made	O
using	O
IPv6	B-Protocol
,	O
and	O
ircs	B-Protocol
specifies	O
a	O
secure	O
connection	O
.	O
</s>
<s>
Per	O
the	O
specification	O
,	O
the	O
usual	O
hash	B-Algorithm
symbol	O
( #	O
)	O
will	O
be	O
prepended	O
to	O
channel	O
names	O
that	O
begin	O
with	O
an	O
alphanumeric	O
character	O
—	O
allowing	O
it	O
to	O
be	O
omitted	O
.	O
</s>
<s>
Some	O
implementations	O
(	O
for	O
example	O
,	O
mIRC	B-Language
)	O
will	O
do	O
so	O
unconditionally	O
resulting	O
in	O
a	O
(	O
usually	O
unintended	O
)	O
extra	O
(	O
for	O
example	O
,	O
#	O
#channel	O
)	O
,	O
if	O
included	O
in	O
the	O
URL	O
.	O
</s>
<s>
Issues	O
in	O
the	O
original	O
design	O
of	O
IRC	B-Protocol
were	O
the	O
amount	O
of	O
shared	O
state	O
data	O
being	O
a	O
limitation	O
on	O
its	O
scalability	O
,	O
the	O
absence	O
of	O
unique	O
user	O
identifications	O
leading	O
to	O
the	O
nickname	O
collision	O
problem	O
,	O
lack	O
of	O
protection	O
from	O
netsplits	B-Error_Name
by	O
means	O
of	O
cyclic	O
routing	O
,	O
the	O
trade-off	O
in	O
scalability	O
for	O
the	O
sake	O
of	O
real-time	O
user	O
presence	O
information	O
,	O
protocol	O
weaknesses	O
providing	O
a	O
platform	O
for	O
abuse	O
,	O
no	O
transparent	O
and	O
optimizable	O
message	O
passing	O
,	O
and	O
no	O
encryption	O
.	O
</s>
<s>
Some	O
of	O
these	O
issues	O
have	O
been	O
addressed	O
in	O
Modern	O
IRC	B-Protocol
.	O
</s>
<s>
Because	O
IRC	B-Protocol
connections	O
may	O
be	O
unencrypted	O
and	O
typically	O
span	O
long	O
time	O
periods	O
,	O
they	O
are	O
an	O
attractive	O
target	O
for	O
DoS/DDoS	O
attackers	O
and	O
hackers	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
careful	O
security	O
policy	O
is	O
necessary	O
to	O
ensure	O
that	O
an	O
IRC	B-Protocol
network	I-Protocol
is	O
not	O
susceptible	O
to	O
an	O
attack	O
such	O
as	O
a	O
takeover	O
war	O
.	O
</s>
<s>
IRC	B-Protocol
networks	I-Protocol
may	O
also	O
K-line	O
or	O
G-line	O
users	O
or	O
servers	O
that	O
have	O
a	O
harming	O
effect	O
.	O
</s>
<s>
Some	O
IRC	B-Protocol
servers	O
support	O
SSL/TLS	B-Protocol
connections	O
for	O
security	O
purposes	O
.	O
</s>
<s>
This	O
helps	O
stop	O
the	O
use	O
of	O
packet	B-Protocol
sniffer	I-Protocol
programs	O
to	O
obtain	O
the	O
passwords	O
of	O
IRC	B-Protocol
users	O
,	O
but	O
has	O
little	O
use	O
beyond	O
this	O
scope	O
due	O
to	O
the	O
public	O
nature	O
of	O
IRC	B-Protocol
channels	O
.	O
</s>
<s>
SSL	O
connections	O
require	O
both	O
client	B-Protocol
and	O
server	B-Application
support	O
(	O
that	O
may	O
require	O
the	O
user	O
to	O
install	O
SSL	O
binaries	O
and	O
IRC	B-Protocol
client	B-Protocol
specific	O
patches	O
or	O
modules	O
on	O
their	O
computers	O
)	O
.	O
</s>
<s>
Some	O
networks	O
also	O
use	O
SSL	O
for	O
server-to-server	O
connections	O
,	O
and	O
provide	O
a	O
special	O
channel	O
flag	O
(	O
such	O
as	O
+S	O
)	O
to	O
only	O
allow	O
SSL-connected	O
users	O
on	O
the	O
channel	O
,	O
while	O
disallowing	O
operator	O
identification	O
in	O
clear	O
text	O
,	O
to	O
better	O
utilize	O
the	O
advantages	O
that	O
SSL	O
provides	O
.	O
</s>
<s>
IRC	B-Protocol
served	O
as	O
an	O
early	O
laboratory	O
for	O
many	O
kinds	O
of	O
Internet	O
attacks	O
,	O
such	O
as	O
using	O
fake	O
ICMP	B-Protocol
unreachable	O
messages	O
to	O
break	O
TCP-based	O
IRC	B-Protocol
connections	O
(	O
nuking	O
)	O
to	O
annoy	O
users	O
or	O
facilitate	O
takeovers	O
.	O
</s>
<s>
One	O
of	O
the	O
most	O
contentious	O
technical	O
issues	O
surrounding	O
IRC	B-Protocol
implementations	O
,	O
which	O
survives	O
to	O
this	O
day	O
,	O
is	O
the	O
merit	O
of	O
"	O
Nick/Channel	O
Delay	O
"	O
vs.	O
"	O
Timestamp	O
"	O
protocols	O
.	O
</s>
<s>
The	O
problem	O
with	O
the	O
original	O
IRC	B-Protocol
protocol	O
as	O
implemented	O
was	O
that	O
when	O
two	O
servers	O
split	O
and	O
rejoined	O
,	O
the	O
two	O
sides	O
of	O
the	O
network	O
would	O
simply	O
merge	O
their	O
channels	O
.	O
</s>
<s>
If	O
a	O
user	O
could	O
join	O
on	O
a	O
"	O
split	O
"	O
server	B-Application
,	O
where	O
a	O
channel	O
that	O
existed	O
on	O
the	O
other	O
side	O
of	O
the	O
network	O
was	O
empty	O
,	O
and	O
gain	O
operator	O
status	O
,	O
they	O
would	O
become	O
a	O
channel	O
operator	O
of	O
the	O
"	O
combined	O
"	O
channel	O
after	O
the	O
netsplit	B-Error_Name
ended	O
;	O
if	O
a	O
user	O
took	O
a	O
nickname	O
that	O
existed	O
on	O
the	O
other	O
side	O
of	O
the	O
network	O
,	O
the	O
server	B-Application
would	O
kill	O
both	O
users	O
when	O
rejoining	O
(	O
a	O
"	O
nick	O
collision	O
"	O
)	O
.	O
</s>
<s>
Apart	O
from	O
causing	O
problems	O
within	O
IRC	B-Protocol
,	O
this	O
encouraged	O
people	O
to	O
conduct	O
denial-of-service	O
attacks	O
against	O
IRC	B-Protocol
servers	O
in	O
order	O
to	O
cause	O
netsplits	B-Error_Name
,	O
which	O
they	O
would	O
then	O
abuse	O
.	O
</s>
<s>
After	O
a	O
user	O
signs	O
off	O
and	O
the	O
nickname	O
becomes	O
available	O
,	O
or	O
a	O
channel	O
ceases	O
to	O
exist	O
because	O
all	O
its	O
users	O
parted	O
(	O
as	O
often	O
happens	O
during	O
a	O
netsplit	B-Error_Name
)	O
,	O
the	O
server	B-Application
will	O
not	O
allow	O
any	O
user	O
to	O
use	O
that	O
nickname	O
or	O
join	O
that	O
channel	O
,	O
until	O
a	O
certain	O
period	O
of	O
time	O
(	O
the	O
delay	O
)	O
has	O
passed	O
.	O
</s>
<s>
The	O
idea	O
behind	O
this	O
is	O
that	O
even	O
if	O
a	O
netsplit	B-Error_Name
occurs	O
,	O
it	O
is	O
useless	O
to	O
an	O
abuser	O
because	O
they	O
cannot	O
take	O
the	O
nickname	O
or	O
gain	O
operator	O
status	O
on	O
a	O
channel	O
,	O
and	O
thus	O
no	O
collision	O
of	O
a	O
nickname	O
or	O
"	O
merging	O
"	O
of	O
a	O
channel	O
can	O
occur	O
.	O
</s>
<s>
When	O
a	O
netsplit	B-Error_Name
occurs	O
,	O
two	O
users	O
on	O
each	O
side	O
are	O
free	O
to	O
use	O
the	O
same	O
nickname	O
or	O
channel	O
,	O
but	O
when	O
the	O
two	O
sides	O
are	O
joined	O
,	O
only	O
one	O
can	O
survive	O
.	O
</s>
<s>
Some	O
modern	O
TS-based	O
IRC	B-Protocol
servers	O
have	O
also	O
incorporated	O
some	O
form	O
of	O
ND	O
and/or	O
CD	O
in	O
addition	O
to	O
timestamping	O
in	O
an	O
attempt	O
to	O
further	O
curb	O
abuse	O
.	O
</s>
<s>
This	O
mechanism	O
assigns	O
every	O
client	B-Protocol
a	O
UID	O
upon	O
connecting	O
to	O
an	O
IRC	B-Protocol
server	B-Application
.	O
</s>
<s>
If	O
two	O
clients	O
with	O
the	O
same	O
nickname	O
join	O
from	O
different	O
sides	O
of	O
a	O
netsplit	B-Error_Name
(	O
"	O
nick	O
collision	O
"	O
)	O
,	O
the	O
first	O
server	B-Application
to	O
see	O
this	O
collision	O
will	O
force	O
both	O
clients	O
to	O
change	O
their	O
nick	O
to	O
their	O
UID	O
,	O
thus	O
saving	O
both	O
clients	O
from	O
being	O
disconnected	O
.	O
</s>
<s>
Client	B-Protocol
software	I-Protocol
exists	O
for	O
various	O
operating	B-General_Concept
systems	I-General_Concept
or	O
software	O
packages	O
,	O
as	O
well	O
as	O
web-based	B-Application
or	O
inside	O
games	O
.	O
</s>
<s>
Many	O
different	O
clients	O
are	O
available	O
for	O
the	O
various	O
operating	B-General_Concept
systems	I-General_Concept
,	O
including	O
Windows	B-Application
,	O
Unix	B-Application
and	O
Linux	B-Application
,	O
macOS	B-Application
and	O
mobile	O
operating	B-General_Concept
systems	I-General_Concept
(	O
such	O
as	O
iOS	B-Application
and	O
Android	B-Application
)	O
.	O
</s>
<s>
On	O
Windows	B-Application
,	O
mIRC	B-Language
is	O
one	O
of	O
the	O
most	O
popular	O
clients	O
.	O
</s>
<s>
Some	O
programs	O
which	O
are	O
extensible	O
through	O
plug-ins	B-Application
also	O
serve	O
as	O
platforms	O
for	O
IRC	B-Protocol
clients	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
client	B-Protocol
called	O
ERC	B-Operating_System
,	O
written	O
entirely	O
in	O
Emacs	B-Operating_System
Lisp	I-Operating_System
,	O
is	O
included	O
in	O
v.22.3	O
of	O
Emacs	O
.	O
</s>
<s>
Therefore	O
,	O
any	O
platform	O
that	O
can	O
run	O
Emacs	O
can	O
run	O
ERC	B-Operating_System
.	O
</s>
<s>
A	O
number	O
of	O
web	B-Application
browsers	I-Application
have	O
built-in	O
IRC	B-Protocol
clients	O
,	O
such	O
as	O
Opera	B-Application
(	O
version	O
12.18	O
and	O
earlier	O
)	O
and	O
the	O
ChatZilla	B-Operating_System
add-on	O
for	O
Mozilla	B-Application
Firefox	I-Application
(	O
for	O
Firefox	B-Application
56	O
and	O
earlier	O
;	O
included	O
as	O
a	O
built-in	O
component	O
of	O
SeaMonkey	B-Language
)	O
.	O
</s>
<s>
Web-based	B-Application
clients	O
,	O
such	O
as	O
Mibbit	O
and	O
open	O
source	O
KiwiIRC	O
,	O
can	O
run	O
in	O
most	O
browsers	B-Application
.	O
</s>
<s>
Games	O
such	O
as	O
War§ow	B-Application
,	O
Unreal	B-Operating_System
Tournament	I-Operating_System
(	O
up	O
to	O
Unreal	B-Application
Tournament	I-Application
2004	I-Application
)	O
,	O
Uplink	B-Application
,	O
Spring	O
Engine-based	O
games	O
,	O
0	B-Application
A.D.	I-Application
and	O
ZDaemon	O
have	O
included	O
IRC	B-Protocol
.	O
</s>
<s>
Ustream	B-Application
's	O
chat	O
interface	O
is	O
IRC	B-Protocol
with	O
custom	O
authentication	O
as	O
well	O
as	O
Twitch	O
's	O
(	O
formerly	O
Justin.tv	O
)	O
.	O
</s>
<s>
A	O
typical	O
use	O
of	O
bots	O
in	O
IRC	B-Protocol
is	O
to	O
provide	O
IRC	B-Protocol
services	O
or	O
specific	O
functionality	O
within	O
a	O
channel	O
such	O
as	O
to	O
host	O
a	O
chat-based	O
game	O
or	O
provide	O
notifications	O
of	O
external	O
events	O
.	O
</s>
<s>
However	O
,	O
some	O
IRC	B-Protocol
bots	O
are	O
used	O
to	O
launch	O
malicious	O
attacks	O
such	O
as	O
denial	O
of	O
service	O
,	O
spamming	O
,	O
or	O
exploitation	O
.	O
</s>
<s>
A	O
program	O
that	O
runs	O
as	O
a	O
daemon	B-Operating_System
on	O
a	O
server	B-Application
and	O
functions	O
as	O
a	O
persistent	O
proxy	B-Application
is	O
known	O
as	O
a	O
BNC	O
or	O
bouncer	O
.	O
</s>
<s>
The	O
purpose	O
is	O
to	O
maintain	O
a	O
connection	O
to	O
an	O
IRC	B-Protocol
server	B-Application
,	O
acting	O
as	O
a	O
relay	O
between	O
the	O
server	B-Application
and	O
client	B-Protocol
,	O
or	O
simply	O
to	O
act	O
as	O
a	O
proxy	B-Application
.	O
</s>
<s>
Should	O
the	O
client	B-Protocol
lose	O
network	O
connectivity	O
,	O
the	O
BNC	O
may	O
stay	O
connected	O
and	O
archive	O
all	O
traffic	O
for	O
later	O
delivery	O
,	O
allowing	O
the	O
user	O
to	O
resume	O
their	O
IRC	B-Protocol
session	O
without	O
disrupting	O
their	O
connection	O
to	O
the	O
server	B-Application
.	O
</s>
<s>
Furthermore	O
,	O
as	O
a	O
way	O
of	O
obtaining	O
a	O
bouncer-like	O
effect	O
,	O
an	O
IRC	B-Protocol
client	B-Protocol
(	O
typically	O
text-based	B-Application
,	O
for	O
example	O
Irssi	B-Protocol
)	O
may	O
be	O
run	O
on	O
an	O
always-on	O
server	B-Application
to	O
which	O
the	O
user	O
connects	O
via	O
ssh	B-Protocol
.	O
</s>
<s>
This	O
also	O
allows	O
devices	O
that	O
only	O
have	O
ssh	B-Protocol
functionality	O
,	O
but	O
no	O
actual	O
IRC	B-Protocol
client	B-Protocol
installed	O
themselves	O
,	O
to	O
connect	O
to	O
the	O
IRC	B-Protocol
,	O
and	O
it	O
allows	O
sharing	O
of	O
IRC	B-Protocol
sessions	O
.	O
</s>
<s>
To	O
keep	O
the	O
IRC	B-Protocol
client	B-Protocol
from	O
quitting	O
when	O
the	O
ssh	B-Protocol
connection	O
closes	O
,	O
the	O
client	B-Protocol
can	O
be	O
run	O
inside	O
a	O
terminal	O
multiplexer	O
such	O
as	O
GNU	B-Application
Screen	I-Application
or	O
tmux	B-Language
,	O
thus	O
staying	O
connected	O
to	O
the	O
IRC	B-Protocol
network(s )	O
constantly	O
and	O
able	O
to	O
log	O
conversation	O
in	O
channels	O
that	O
the	O
user	O
is	O
interested	O
in	O
,	O
or	O
to	O
maintain	O
a	O
channel	O
's	O
presence	O
on	O
the	O
network	O
.	O
</s>
<s>
Modelled	O
after	O
this	O
setup	O
,	O
in	O
2004	O
an	O
IRC	B-Protocol
client	B-Protocol
following	O
the	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
,	O
called	O
Smuxi	B-Protocol
,	O
was	O
launched	O
.	O
</s>
<s>
There	O
are	O
numerous	O
search	O
engines	O
available	O
to	O
aid	O
the	O
user	O
in	O
finding	O
what	O
they	O
are	O
looking	O
for	O
on	O
IRC	B-Protocol
.	O
</s>
<s>
It	O
is	O
responsible	O
for	O
crawling	O
IRC	B-Protocol
servers	O
to	O
index	O
the	O
information	O
being	O
sent	O
across	O
them	O
.	O
</s>
<s>
The	O
storage	O
method	O
is	O
usually	O
some	O
sort	O
of	O
relational	O
database	O
,	O
like	O
MySQL	B-Application
or	O
Oracle	B-General_Concept
.	O
</s>
<s>
Most	O
search	O
engines	O
have	O
their	O
own	O
spider	O
that	O
is	O
a	O
single	O
application	O
responsible	O
for	O
crawling	O
IRC	B-Protocol
and	O
indexing	O
data	O
itself	O
;	O
however	O
,	O
others	O
are	O
"	O
user	O
based	O
"	O
indexers	O
.	O
</s>
<s>
The	O
latter	O
rely	O
on	O
users	O
to	O
install	O
their	O
"	O
add-on	O
"	O
to	O
their	O
IRC	B-Protocol
client	B-Protocol
;	O
the	O
add-on	O
is	O
what	O
sends	O
the	O
database	O
the	O
channel	O
information	O
of	O
whatever	O
channels	O
the	O
user	O
happens	O
to	O
be	O
on	O
.	O
</s>
<s>
Many	O
users	O
have	O
implemented	O
their	O
own	O
ad	O
hoc	O
search	O
engines	O
using	O
the	O
logging	O
features	O
built	O
into	O
many	O
IRC	B-Protocol
clients	O
.	O
</s>
<s>
IRC	B-Protocol
still	O
lacks	O
a	O
single	O
globally	O
accepted	O
standard	O
convention	O
for	O
how	O
to	O
transmit	O
characters	O
outside	O
the	O
7-bit	B-Protocol
ASCII	I-Protocol
repertoire	O
.	O
</s>
<s>
IRC	B-Protocol
servers	O
normally	O
transfer	O
messages	O
from	O
a	O
client	B-Protocol
to	O
another	O
client	B-Protocol
just	O
as	O
byte	O
sequences	O
,	O
without	O
any	O
interpretation	O
or	O
recoding	O
of	O
characters	O
.	O
</s>
<s>
The	O
IRC	B-Protocol
protocol	O
(	O
unlike	O
e.g.	O
</s>
<s>
MIME	B-Protocol
or	O
HTTP	B-Protocol
)	O
lacks	O
mechanisms	O
for	O
announcing	O
and	O
negotiating	O
character	B-General_Concept
encoding	I-General_Concept
options	O
.	O
</s>
<s>
This	O
has	O
put	O
the	O
responsibility	O
for	O
choosing	O
the	O
appropriate	O
character	O
codec	O
on	O
the	O
client	B-Protocol
.	O
</s>
<s>
In	O
practice	O
,	O
IRC	B-Protocol
channels	O
have	O
largely	O
used	O
the	O
same	O
character	B-General_Concept
encodings	I-General_Concept
that	O
were	O
also	O
used	O
by	O
operating	B-General_Concept
systems	I-General_Concept
(	O
in	O
particular	O
Unix	B-Application
derivatives	O
)	O
in	O
the	O
respective	O
language	O
communities	O
:	O
</s>
<s>
7-bit	O
era	O
:	O
In	O
the	O
early	O
days	O
of	O
IRC	B-Protocol
,	O
especially	O
among	O
Scandinavian	O
and	O
Finnish	O
language	O
users	O
,	O
national	O
variants	O
of	O
ISO	O
646	O
were	O
the	O
dominant	O
character	B-General_Concept
encodings	I-General_Concept
.	O
</s>
<s>
These	O
encode	O
non-ASCII	O
characters	O
like	O
Ä	O
Ö	O
Å	O
ä	O
ö	O
å	O
at	O
code	O
positions	O
0x5B	O
0x5C	O
0x5D	O
0x7B	O
0x7C	O
0x7D	O
(	O
US-ASCII	B-Protocol
:	O
[	O
\	O
]	O
{	O
|	O
}	O
)	O
.	O
</s>
<s>
By	O
the	O
late	O
1990s	O
,	O
the	O
use	O
of	O
7-bit	O
encodings	O
had	O
disappeared	O
in	O
favour	O
of	O
ISO	O
8859-1	O
,	O
and	O
such	O
equivalence	O
mappings	O
were	O
dropped	O
from	O
some	O
IRC	B-Protocol
daemons	B-Operating_System
.	O
</s>
<s>
Russian	O
users	O
had	O
a	O
choice	O
of	O
KOI8-R	O
,	O
ISO	O
8859-5	O
and	O
CP1251	O
,	O
and	O
since	O
about	O
2000	O
,	O
modern	O
Russian	O
IRC	B-Protocol
networks	I-Protocol
convert	O
between	O
these	O
different	O
commonly	O
used	O
encodings	O
of	O
the	O
Cyrillic	O
script	O
.	O
</s>
<s>
Multi-byte	O
era	O
:	O
For	O
a	O
long	O
time	O
,	O
East	O
Asian	O
IRC	B-Protocol
channels	O
with	O
logographic	O
scripts	O
in	O
China	O
,	O
Japan	O
,	O
and	O
Korea	O
have	O
been	O
using	O
multi-byte	O
encodings	O
such	O
as	O
EUC	O
or	O
ISO-2022-JP	O
.	O
</s>
<s>
With	O
the	O
common	O
migration	O
from	O
ISO	O
8859	O
to	O
UTF-8	O
on	O
Linux	B-Application
and	O
Unix	B-Application
platforms	O
since	O
about	O
2002	O
,	O
UTF-8	O
has	O
become	O
an	O
increasingly	O
popular	O
substitute	O
for	O
many	O
of	O
the	O
previously	O
used	O
8-bit	O
encodings	O
in	O
European	O
channels	O
.	O
</s>
<s>
Some	O
IRC	B-Protocol
clients	O
are	O
now	O
capable	O
of	O
reading	O
messages	O
both	O
in	O
ISO	O
8859-1	O
or	O
UTF-8	O
in	O
the	O
same	O
channel	O
,	O
heuristically	O
autodetecting	O
which	O
encoding	O
is	O
used	O
.	O
</s>
<s>
The	O
shift	O
to	O
UTF-8	O
began	O
in	O
particular	O
on	O
Finnish-speaking	O
IRC	B-Protocol
(	O
Merkistö	O
(	O
Finnish	O
)	O
)	O
.	O
</s>
<s>
Today	O
,	O
the	O
UTF-8	O
encoding	O
of	O
Unicode/ISO	O
10646	O
would	O
be	O
the	O
most	O
likely	O
contender	O
for	O
a	O
single	O
future	O
standard	O
character	B-General_Concept
encoding	I-General_Concept
for	O
all	O
IRC	B-Protocol
communication	O
,	O
if	O
such	O
standard	O
ever	O
relaxed	O
the	O
510-byte	O
message	O
size	O
restriction	O
.	O
</s>
<s>
UTF-8	O
is	O
ASCII	B-Protocol
compatible	O
and	O
covers	O
the	O
superset	O
of	O
all	O
other	O
commonly	O
used	O
coded	B-General_Concept
character	I-General_Concept
set	I-General_Concept
standards	O
.	O
</s>
<s>
Much	O
like	O
conventional	O
P2P	O
file	O
sharing	O
,	O
users	O
can	O
create	O
file	O
servers	O
that	O
allow	O
them	O
to	O
share	O
files	O
with	O
each	O
other	O
by	O
using	O
customised	O
IRC	B-Protocol
bots	O
or	O
scripts	O
for	O
their	O
IRC	B-Protocol
client	B-Protocol
.	O
</s>
<s>
Often	O
users	O
will	O
group	O
together	O
to	O
distribute	O
warez	B-Application
via	O
a	O
network	O
of	O
IRC	B-Protocol
bots	O
.	O
</s>
<s>
Technically	O
,	O
IRC	B-Protocol
provides	O
no	O
file	B-Protocol
transfer	I-Protocol
mechanisms	O
itself	O
;	O
file	O
sharing	O
is	O
implemented	O
by	O
IRC	B-Protocol
clients	O
,	O
typically	O
using	O
the	O
Direct	O
Client-to-Client	O
(	O
DCC	O
)	O
protocol	O
,	O
in	O
which	O
file	B-Protocol
transfers	I-Protocol
are	O
negotiated	O
through	O
the	O
exchange	O
of	O
private	B-Application
messages	I-Application
between	O
clients	O
.	O
</s>
<s>
The	O
vast	O
majority	O
of	O
IRC	B-Protocol
clients	O
feature	O
support	O
for	O
DCC	O
file	B-Protocol
transfers	I-Protocol
,	O
hence	O
the	O
view	O
that	O
file	O
sharing	O
is	O
an	O
integral	O
feature	O
of	O
IRC	B-Protocol
.	O
</s>
<s>
DCC	O
commands	O
have	O
also	O
been	O
used	O
to	O
exploit	O
vulnerable	O
clients	O
into	O
performing	O
an	O
action	O
such	O
as	O
disconnecting	O
from	O
the	O
server	B-Application
or	O
exiting	O
the	O
client	B-Protocol
.	O
</s>
