<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
source	B-Protocol
routing	I-Protocol
,	O
also	O
called	O
path	O
addressing	O
,	O
allows	O
a	O
sender	O
of	O
a	O
packet	B-Protocol
to	O
partially	O
or	O
completely	O
specify	O
the	O
route	B-Protocol
the	O
packet	B-Protocol
takes	O
through	O
the	O
network	O
.	O
</s>
<s>
In	O
contrast	O
,	O
in	O
conventional	O
routing	B-Protocol
,	O
routers	O
in	O
the	O
network	O
determine	O
the	O
path	O
incrementally	O
based	O
on	O
the	O
packet	B-Protocol
's	O
destination	O
.	O
</s>
<s>
Another	O
routing	B-Protocol
alternative	O
,	O
label	B-Protocol
switching	I-Protocol
,	O
is	O
used	O
in	O
connection-oriented	O
networks	O
such	O
as	O
X.25	B-Protocol
,	O
Frame	B-Protocol
Relay	I-Protocol
,	O
Asynchronous	O
Transfer	O
Mode	O
and	O
Multiprotocol	B-Protocol
Label	I-Protocol
Switching	I-Protocol
.	O
</s>
<s>
Source	B-Protocol
routing	I-Protocol
allows	O
easier	O
troubleshooting	O
,	O
improved	O
traceroute	B-Protocol
,	O
and	O
enables	O
a	O
node	O
to	O
discover	O
all	O
the	O
possible	O
routes	O
to	O
a	O
host	O
.	O
</s>
<s>
It	O
does	O
not	O
allow	O
a	O
source	O
to	O
directly	O
manage	O
network	O
performance	O
by	O
forcing	O
packets	B-Protocol
to	O
travel	O
over	O
one	O
path	O
to	O
prevent	O
congestion	O
on	O
another	O
.	O
</s>
<s>
Many	O
high-performance	O
interconnects	O
including	O
Myrinet	B-General_Concept
,	O
Quadrics	B-General_Concept
,	O
IEEE	O
1355	O
,	O
and	O
SpaceWire	B-Architecture
support	O
source	B-Protocol
routing	I-Protocol
.	O
</s>
<s>
In	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
,	O
two	O
header	O
options	O
are	O
available	O
which	O
are	O
rarely	O
used	O
:	O
"	O
strict	O
source	O
and	O
record	O
route	B-Protocol
"	O
(	O
SSRR	O
)	O
and	O
"	O
loose	O
source	O
and	O
record	O
route	B-Protocol
"	O
(	O
LSRR	O
)	O
.	O
</s>
<s>
Because	O
of	O
security	O
concerns	O
,	O
packets	B-Protocol
marked	O
LSRR	O
are	O
frequently	O
blocked	O
on	O
the	O
Internet	O
.	O
</s>
<s>
If	O
not	O
blocked	O
,	O
LSRR	O
can	O
allow	O
an	O
attacker	O
to	O
spoof	O
an	O
address	O
but	O
still	O
successfully	O
receive	O
response	O
packets	B-Protocol
by	O
forcing	O
return	O
traffic	O
for	O
spoofed	O
packets	B-Protocol
to	O
return	O
through	O
the	O
attacker	O
's	O
device	O
.	O
</s>
<s>
In	O
IPv6	B-Protocol
,	O
two	O
forms	O
of	O
source	B-Protocol
routing	I-Protocol
have	O
been	O
developed	O
.	O
</s>
<s>
The	O
first	O
approach	O
was	O
the	O
Type	O
0	O
Routing	B-Protocol
header	O
.	O
</s>
<s>
This	O
routing	B-Protocol
header	O
was	O
designed	O
to	O
support	O
the	O
same	O
use	O
cases	O
as	O
the	O
IPv4	O
header	O
options	O
.	O
</s>
<s>
Unfortunately	O
there	O
were	O
several	O
significant	O
attacks	O
against	O
this	O
routing	B-Protocol
header	O
and	O
its	O
utilisation	O
was	O
deprecated	O
.	O
</s>
<s>
A	O
more	O
secure	O
form	O
of	O
source	B-Protocol
routing	I-Protocol
is	O
being	O
developed	O
within	O
the	O
IETF	O
to	O
support	O
the	O
IPv6	B-Protocol
version	O
of	O
Segment	B-Protocol
Routing	I-Protocol
.	O
</s>
<s>
Software-defined	O
networking	O
can	O
also	O
be	O
enhanced	O
when	O
source	B-Protocol
routing	I-Protocol
is	O
used	O
in	O
the	O
forwarding	O
plane	O
.	O
</s>
<s>
When	O
using	O
source	B-Protocol
routing	I-Protocol
with	O
Myrinet	B-General_Concept
,	O
the	O
sender	O
of	O
the	O
packet	B-Protocol
prepends	O
the	O
complete	O
route	B-Protocol
,	O
one	O
byte	O
for	O
every	O
crossbar	O
,	O
to	O
each	O
packet	B-Protocol
header	O
.	O
</s>
<s>
Each	O
crossbar	O
examines	O
the	O
first	O
routing	B-Protocol
byte	O
of	O
the	O
packet	B-Protocol
.	O
</s>
<s>
When	O
using	O
source	B-Protocol
routing	I-Protocol
,	O
that	O
byte	O
indicates	O
a	O
particular	O
port	O
of	O
that	O
crossbar	O
;	O
when	O
that	O
port	O
becomes	O
available	O
,	O
the	O
router	O
discards	O
that	O
routing	B-Protocol
byte	O
and	O
sends	O
the	O
rest	O
of	O
the	O
packet	B-Protocol
out	O
that	O
port	O
.	O
</s>
<s>
Each	O
packet	B-Protocol
traveling	O
through	O
a	O
SpaceWire	B-Architecture
network	O
can	O
use	O
path	O
addressing	O
(	O
source	B-Protocol
routing	I-Protocol
)	O
or	O
logical	O
addressing	O
or	O
some	O
combination	O
.	O
</s>
<s>
The	O
router	O
examines	O
the	O
first	O
data	O
character	O
of	O
the	O
packet	B-Protocol
;	O
when	O
it	O
indicates	O
some	O
specific	O
port	O
of	O
the	O
router	O
,	O
the	O
router	O
discards	O
that	O
routing	B-Protocol
character	O
and	O
sends	O
the	O
rest	O
of	O
the	O
packet	B-Protocol
out	O
that	O
port	O
.	O
</s>
