<s>
Bogon	B-Protocol
filtering	I-Protocol
is	O
the	O
practice	O
of	O
filtering	O
bogons	B-Protocol
,	O
which	O
are	O
bogus	O
(	O
fake	O
)	O
IP	B-Protocol
addresses	I-Protocol
of	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
Bogons	B-Protocol
include	O
IP	B-Protocol
packets	B-Protocol
on	O
the	O
public	O
Internet	O
that	O
contain	O
addresses	O
that	O
are	O
not	O
in	O
any	O
range	O
allocated	O
or	O
delegated	O
by	O
the	O
Internet	O
Assigned	O
Numbers	O
Authority	O
(	O
IANA	O
)	O
or	O
a	O
delegated	O
regional	O
Internet	O
registry	O
(	O
RIR	O
)	O
and	O
allowed	O
for	O
public	O
Internet	O
use	O
.	O
</s>
<s>
The	O
areas	O
of	O
unallocated	O
address	O
space	O
are	O
called	O
the	O
bogon	B-Protocol
space	I-Protocol
.	O
</s>
<s>
Bogons	B-Protocol
also	O
include	O
some	O
address	O
ranges	O
from	O
allocated	O
space	O
,	O
also	O
known	O
as	O
Martian	B-Protocol
packets	I-Protocol
,	O
mainly	O
when	O
they	O
are	O
being	O
used	O
as	O
source	O
address	O
.	O
</s>
<s>
Addresses	O
reserved	O
for	O
private	B-Protocol
networks	I-Protocol
,	O
such	O
as	O
those	O
in	O
,	O
,	O
and	O
,	O
loopback	B-Protocol
interfaces	I-Protocol
like	O
and	O
,	O
and	O
link-local	B-Protocol
addresses	I-Protocol
like	O
and	O
are	O
part	O
of	O
it	O
.	O
</s>
<s>
Also	O
addresses	O
for	O
Carrier-grade	B-Protocol
NAT	I-Protocol
,	O
Teredo	B-Protocol
,	O
and	O
6to4	B-Protocol
and	O
documentation	O
prefixes	O
fall	O
into	O
this	O
category	O
.	O
</s>
<s>
Many	O
ISPs	O
and	O
end-user	O
firewalls	B-Application
filter	O
and	O
block	O
bogons	B-Protocol
,	O
because	O
they	O
have	O
no	O
legitimate	O
use	O
,	O
and	O
usually	O
are	O
the	O
result	O
of	O
accidental	O
misconfiguration	O
or	O
malicious	O
intent	O
.	O
</s>
<s>
Bogons	B-Protocol
can	O
be	O
filtered	O
by	O
using	O
router	B-Protocol
access-control	O
lists	O
(	O
ACLs	O
)	O
,	O
or	O
by	O
BGP	B-Protocol
blackholing	B-Protocol
.	O
</s>
<s>
IP	B-Protocol
addresses	I-Protocol
that	O
are	O
currently	O
in	O
the	O
bogon	B-Protocol
space	I-Protocol
may	O
not	O
be	O
bogons	B-Protocol
at	O
a	O
later	O
date	O
because	O
IANA	O
and	O
other	O
registries	O
frequently	O
assign	O
new	O
address	O
space	O
to	O
ISPs	O
.	O
</s>
<s>
Announcements	O
of	O
new	O
assignments	O
are	O
often	O
published	O
on	O
network	B-Architecture
operators	O
 '	O
mailing	O
lists	O
(	O
such	O
as	O
NANOG	O
)	O
to	O
ensure	O
that	O
operators	O
have	O
a	O
chance	O
to	O
remove	O
bogon	B-Protocol
filtering	I-Protocol
for	O
addresses	O
that	O
have	O
become	O
legitimate	O
.	O
</s>
<s>
,	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
recommends	O
that	O
,	O
since	O
there	O
are	O
no	O
longer	O
any	O
unallocated	O
IPv4	O
s	O
,	O
IPv4	O
bogon	B-Protocol
filters	I-Protocol
based	O
on	O
registration	O
status	O
should	O
be	O
removed	O
.	O
</s>
<s>
However	O
,	O
bogon	B-Protocol
filters	I-Protocol
still	O
need	O
to	O
check	O
for	O
Martian	B-Protocol
packets	I-Protocol
.	O
</s>
<s>
The	O
term	O
bogon	B-Protocol
stems	O
from	O
hacker	O
jargon	O
,	O
with	O
the	O
earliest	O
appearance	O
in	O
the	O
Jargon	O
File	O
in	O
version	O
1.5.0	O
(	O
dated	O
1983	O
)	O
.	O
</s>
<s>
A	O
bogon	B-Protocol
packet	B-Protocol
is	O
frequently	O
bogus	O
both	O
in	O
the	O
conventional	O
sense	O
of	O
being	O
forged	O
for	O
illegitimate	O
purposes	O
,	O
and	O
in	O
the	O
hackish	O
sense	O
of	O
being	O
incorrect	O
,	O
absurd	O
,	O
and	O
useless	O
.	O
</s>
<s>
These	O
unused	O
IP	B-Protocol
addresses	I-Protocol
are	O
collectively	O
known	O
as	O
a	O
bogon	B-Protocol
,	O
a	O
contraction	O
of	O
"	O
bogus	O
logon	O
"	O
,	O
or	O
a	O
logon	O
from	O
a	O
place	O
you	O
know	O
no	O
one	O
can	O
actually	O
logon	O
.	O
</s>
