<s>
Broadcast	B-Protocol
,	I-Protocol
unknown-unicast	I-Protocol
and	I-Protocol
multicast	I-Protocol
traffic	I-Protocol
(	O
BUM	B-Protocol
traffic	I-Protocol
)	O
is	O
network	O
traffic	O
transmitted	O
using	O
one	O
of	O
three	O
methods	O
of	O
sending	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
network	O
traffic	O
to	O
a	O
destination	O
of	O
which	O
the	O
sender	O
does	O
not	O
know	O
the	O
network	O
address	O
.	O
</s>
<s>
As	O
a	O
concept	O
related	O
to	O
computer	B-Architecture
networking	I-Architecture
,	O
it	O
includes	O
three	O
types	O
of	O
Ethernet	O
modes	O
:	O
broadcast	B-Operating_System
,	O
unicast	B-Protocol
and	O
multicast	O
Ethernet	O
.	O
</s>
<s>
BUM	B-Protocol
traffic	I-Protocol
refers	O
to	O
that	O
kind	O
of	O
network	O
traffic	O
that	O
will	O
be	O
forwarded	O
to	O
multiple	O
destinations	O
or	O
that	O
cannot	O
be	O
addressed	O
to	O
the	O
intended	O
destination	O
only	O
.	O
</s>
<s>
Broadcast	B-Operating_System
traffic	I-Operating_System
is	O
used	O
to	O
transmit	O
a	O
message	O
to	O
any	O
reachable	O
destination	O
in	O
the	O
network	O
without	O
the	O
need	O
to	O
know	O
any	O
information	O
about	O
the	O
receiving	O
party	O
.	O
</s>
<s>
When	O
broadcast	B-Operating_System
traffic	I-Operating_System
is	O
received	O
by	O
a	O
network	B-Protocol
switch	I-Protocol
it	O
is	O
replicated	O
to	O
all	O
ports	B-Protocol
within	O
the	O
respective	O
VLAN	B-General_Concept
except	O
the	O
one	O
from	O
which	O
the	O
traffic	O
comes	O
from	O
.	O
</s>
<s>
Unknown-unicast	O
traffic	O
happens	O
when	O
a	O
switch	O
receives	O
unicast	B-Protocol
traffic	O
intended	O
to	O
be	O
delivered	O
to	O
a	O
destination	O
that	O
is	O
not	O
in	O
its	O
forwarding	B-Protocol
information	I-Protocol
base	I-Protocol
.	O
</s>
<s>
In	O
this	O
case	O
the	O
switch	O
marks	O
the	O
frame	B-Protocol
for	O
flooding	B-Protocol
and	O
sends	O
it	O
to	O
all	O
forwarding	O
ports	B-Protocol
within	O
the	O
respective	O
VLAN	B-General_Concept
.	O
</s>
<s>
This	O
flooding	B-Protocol
of	O
packets	O
is	O
known	O
as	O
a	O
unicast	B-Protocol
flooding	B-Protocol
.	O
</s>
<s>
This	O
causes	O
the	O
message	O
to	O
be	O
broadcast	B-Operating_System
when	O
no	O
group	O
management	O
mechanism	O
is	O
present	O
.	O
</s>
<s>
Flooding	B-Protocol
BUM	O
frames	O
is	O
required	O
in	O
transparent	O
bridging	O
and	O
in	O
a	O
data	B-Operating_System
center	I-Operating_System
context	O
this	O
does	B-Architecture
not	I-Architecture
scale	I-Architecture
well	O
causing	O
poor	O
performance	O
.	O
</s>
<s>
One	O
issue	O
that	O
may	O
arise	O
is	O
that	O
some	O
network	O
devices	O
cannot	O
handle	O
high	O
rates	O
of	O
broadcast	B-Operating_System
,	O
unknown-unicast	O
or	O
multicast	O
traffic	O
.	O
</s>
<s>
In	O
such	O
cases	O
,	O
it	O
is	O
possible	O
to	O
limit	O
the	O
BUM	B-Protocol
traffic	I-Protocol
for	O
specific	O
ports	B-Protocol
in	O
order	O
to	O
have	O
a	O
control	O
on	O
the	O
number	O
of	O
packets	O
or	O
bytes	O
that	O
are	O
flooded	O
on	O
the	O
VLAN	B-General_Concept
to	O
other	O
devices	O
.	O
</s>
<s>
This	O
threshold	O
is	O
represented	O
in	O
kilobits	O
per	O
second	O
(	O
kbps	O
)	O
,	O
and	O
it	O
can	O
be	O
set	O
for	O
broadcast	B-Operating_System
rate	O
,	O
multicast	O
rate	O
and	O
unknown	O
unicast	B-Protocol
rate	O
independently	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
unknown-unicast	O
traffic	O
,	O
a	O
security	O
issue	O
may	O
arise	O
.	O
</s>
<s>
To	O
prevent	O
flooding	B-Protocol
unknown-unicast	I-Protocol
traffic	O
across	O
the	O
switch	O
,	O
it	O
is	O
possible	O
to	O
configure	O
the	O
network	O
equipment	O
to	O
divert	O
unknown-unicast	O
traffic	O
to	O
specific	O
trunk	O
interfaces	O
in	O
order	O
to	O
split	O
broadcast	B-Operating_System
coming	O
from	O
different	O
VLANs	B-General_Concept
or	O
to	O
use	O
specific	O
trunk	O
interfaces	O
for	O
multiple	O
VLANs	B-General_Concept
.	O
</s>
<s>
The	O
use	O
of	O
VXLAN	B-Protocol
as	O
overlay	O
technology	O
allows	O
providing	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
connectivity	O
services	O
between	O
endpoints	O
that	O
may	O
be	O
deployed	O
across	O
network	B-Application
layer	I-Application
network	O
domains	O
.	O
</s>
<s>
Since	O
those	O
endpoints	O
are	O
logically	O
part	O
of	O
the	O
same	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
domain	O
,	O
they	O
must	O
be	O
capable	O
of	O
sending	O
and	O
receiving	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
multi-destination	O
frames	O
(	O
BUM	B-Protocol
traffic	I-Protocol
)	O
.	O
</s>
<s>
BUM	B-Protocol
traffic	I-Protocol
can	O
be	O
exchanged	O
across	O
network	B-Application
layer	I-Application
network	O
boundaries	O
by	O
encapsulating	O
it	O
into	O
VXLAN	B-Protocol
packets	O
addressed	O
to	O
a	O
multicast	O
group	O
,	O
so	O
to	O
leverage	O
the	O
network	O
for	O
traffic	O
replication	O
services	O
.	O
</s>
<s>
In	O
Data	O
Plane	O
Learning	O
the	O
broadcast	B-Operating_System
traffic	I-Operating_System
is	O
flooded	O
to	O
multicast	O
group	O
members	O
.	O
</s>
<s>
In	O
Control	O
Plane	O
Learning	O
addresses	O
are	O
collected	O
and	O
forwarded	O
via	O
BGP	B-Protocol
.	O
</s>
<s>
Broadcast	B-Operating_System
traffic	I-Operating_System
is	O
reduced	O
and	O
VXLAN	B-Protocol
tunnel	I-Protocol
endpoints	I-Protocol
(	O
VTEPs	B-Protocol
)	O
reply	O
to	O
the	O
caller	O
directly	O
.	O
</s>
<s>
VXLAN	B-Protocol
can	O
handle	O
BUM	O
in	O
two	O
ways	O
:	O
Multicast	O
and	O
Head	O
End	O
Replication	O
.	O
</s>
<s>
Multicast	O
is	O
the	O
most	O
common	O
approach	O
,	O
and	O
each	O
VXLAN	B-Protocol
network	O
identifier	O
(	O
VNI	O
)	O
is	O
mapped	O
to	O
a	O
single	O
multicast	O
group	O
,	O
while	O
each	O
multicast	O
group	O
may	O
map	O
to	O
one	O
or	O
more	O
VNIs	O
.	O
</s>
<s>
When	O
a	O
VTEP	B-Protocol
comes	O
alive	O
it	O
uses	O
the	O
Internet	B-Protocol
Group	I-Protocol
Management	I-Protocol
Protocol	I-Protocol
to	O
join	O
the	O
multicast	O
groups	O
for	O
the	O
VNIs	O
it	O
uses	O
.	O
</s>
<s>
When	O
a	O
VTEP	B-Protocol
has	O
to	O
send	O
BUM	B-Protocol
traffic	I-Protocol
it	O
will	O
send	O
it	O
only	O
to	O
the	O
relevant	O
multicast	O
group	O
.	O
</s>
<s>
This	O
is	O
a	O
method	O
for	O
VTEP	B-Protocol
discovery	O
.	O
</s>
<s>
Head	O
End	O
Replication	O
is	O
only	O
available	O
if	O
using	O
BGP	B-Protocol
EVPN	O
.	O
</s>
<s>
It	O
is	O
less	O
efficient	O
than	O
multicast	O
and	O
does	B-Architecture
not	I-Architecture
scale	I-Architecture
well	O
but	O
it	O
is	O
simpler	O
to	O
implement	O
if	O
you	O
do	O
not	O
have	O
a	O
multicast-enabled	O
infrastructure	O
.	O
</s>
<s>
In	O
Head	O
End	O
Replication	O
,	O
when	O
BUM	O
arrives	O
,	O
the	O
VTEP	B-Protocol
creates	O
several	O
unicast	B-Protocol
packets	O
and	O
sends	O
one	O
to	O
each	O
VTEP	B-Protocol
that	O
supports	O
the	O
VNI	O
.	O
</s>
<s>
Ethernet	O
VPN	B-Application
(	O
EVPN	O
)	O
and	O
Provider	O
Backbone	O
Bridging	O
EVPN	O
(	O
PBB-EVPN	O
)	O
provide	O
Ethernet	O
multipoint	O
services	O
over	O
MPLS	B-Protocol
networks	O
.	O
</s>
<s>
In	O
EVPN	O
operations	O
,	O
the	O
Provider	O
Edge	O
(	O
PE	O
)	O
routers	O
automatically	O
discover	O
each	O
other	O
when	O
connected	O
on	O
the	O
same	O
ethernet	O
segment	O
and	O
select	O
a	O
Designated	O
Forwarder	O
(	O
DF	O
)	O
responsible	O
for	O
forwarding	O
BUM	B-Protocol
traffic	I-Protocol
.	O
</s>
<s>
In	O
a	O
VXLAN-EVPN	O
,	O
MAC	O
learning	O
occurs	O
via	O
the	O
control	O
plane	O
instead	O
of	O
data	O
plane	O
.	O
</s>
<s>
Furthermore	O
,	O
it	O
is	O
accepted	O
only	O
traffic	O
from	O
VTEPs	B-Protocol
whose	O
information	O
is	O
learnt	O
via	O
the	O
control	O
plane	O
,	O
otherwise	O
it	O
is	O
dropped	O
.	O
</s>
<s>
This	O
presents	O
a	O
secure	O
fabric	O
where	O
traffic	O
will	O
only	O
be	O
forwarded	O
between	O
VTEPs	B-Protocol
validated	O
by	O
the	O
control	O
plane	O
.	O
</s>
