<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
egress	B-Protocol
filtering	I-Protocol
is	O
the	O
practice	O
of	O
monitoring	O
and	O
potentially	O
restricting	O
the	O
flow	O
of	O
information	O
outbound	O
from	O
one	O
network	O
to	O
another	O
.	O
</s>
<s>
Typically	O
,	O
it	O
is	O
information	O
from	O
a	O
private	O
TCP/IP	B-Protocol
computer	B-Architecture
network	I-Architecture
to	O
the	O
Internet	O
that	O
is	O
controlled	O
.	O
</s>
<s>
TCP/IP	B-Protocol
packets	O
that	O
are	O
being	O
sent	O
out	O
of	O
the	O
internal	O
network	O
are	O
examined	O
via	O
a	O
router	B-Protocol
,	O
firewall	B-Application
,	O
or	O
similar	O
edge	B-Device
device	I-Device
.	O
</s>
<s>
Egress	B-Protocol
filtering	I-Protocol
helps	O
ensure	O
that	O
unauthorized	O
or	O
malicious	O
traffic	O
never	O
leaves	O
the	O
internal	O
network	O
.	O
</s>
<s>
In	O
a	O
corporate	O
network	O
,	O
typical	O
recommendations	O
are	O
that	O
all	O
traffic	O
except	O
that	O
emerging	O
from	O
a	O
select	O
set	O
of	O
servers	B-Application
would	O
be	O
denied	O
egress	O
.	O
</s>
<s>
Restrictions	O
can	O
further	O
be	O
made	O
such	O
that	O
only	O
select	O
protocols	O
such	O
as	O
HTTP	B-Protocol
,	O
email	O
,	O
and	O
DNS	B-Protocol
are	O
allowed	O
.	O
</s>
<s>
User	O
workstations	B-Device
would	O
then	O
need	O
to	O
be	O
configured	O
either	O
manually	O
or	O
via	O
proxy	B-Protocol
auto-config	I-Protocol
to	O
use	O
one	O
of	O
the	O
allowed	O
servers	B-Application
as	O
a	O
proxy	B-Application
.	O
</s>
<s>
An	O
edge	B-Device
device	I-Device
at	O
the	O
boundary	O
between	O
the	O
internal	O
corporate	O
network	O
and	O
external	O
networks	O
(	O
such	O
as	O
the	O
Internet	O
)	O
is	O
used	O
to	O
perform	O
egress	O
checks	O
against	O
packets	O
leaving	O
the	O
internal	O
network	O
,	O
verifying	O
that	O
the	O
source	O
IP	B-Protocol
address	I-Protocol
in	O
all	O
outbound	O
packets	O
is	O
within	O
the	O
range	O
of	O
allocated	O
internal	O
address	O
blocks	O
.	O
</s>
<s>
Egress	B-Protocol
filtering	I-Protocol
may	O
require	O
policy	O
changes	O
and	O
administrative	O
work	O
whenever	O
a	O
new	O
application	O
requires	O
external	O
network	O
access	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
egress	B-Protocol
filtering	I-Protocol
is	O
an	O
uncommon	O
feature	O
on	O
consumer	O
and	O
very	O
small	O
business	O
networks	O
.	O
</s>
