MPLS

Teoría de las Comunicaciones
16 de mayo de 2012
• Tunneling.
• Virtual Networks and Tunnels.
• ATM (Asynchronous Transfer
Mode).
• MPLS (Multi-Protocol Label
Switching).
• MPLS. Ejercicio.
1
Tunneling
2
Tunneling a packet from Paris to
London
3
Why tunneling ?
• One reason is security. Supplemented with encryption, a tunnel can
become a very private sort of link across a public network.
• Another reason may be that R1 and R2 have some capabilities that are
not widely available in the intervening networks, such as multicast
routing. By connecting these routers with a tunnel, we can build a virtual
network in which all the routers with this capability appear to be directly
connected.
• A third reason to build tunnels is to carry packets from protocols other
than IP across an IP network. As long as the routers at either end of the
tunnel know how to handle these other protocols, the IP tunnel looks to
them like a point-to-point link over which they can send non-IP packets.
• Tunnels also provide a mechanism by which we can force a packet to be
delivered to a particular place even if its original header—the one that
gets encapsulated inside the tunnel header—might suggest that it should go
somewhere else.
• Thus, we see that tunneling is a powerful and quite general technique for
building virtual links across internetworks.
4
Tunneling does have its downsides
• One is that it increases the length of packets; this
might represent a significant waste of bandwidth for
short packets.
• There may also be performance implications for the
routers at either end of the tunnel, since they need to
do more work than normal forwarding as they add
and remove the tunnel header.
• Finally, there is a management cost for the
administrative entity that is responsible for setting up
the tunnels and making sure they are correctly
handled by the routing protocols.
5
Tunneling: examples
• IP/IP
• GRE (Generic Routing Encapsulation)
– RFCs 1701 y 1702…
• L2TP (Layer 2 Tunneling Protocol)
– RFCs 2661…
• IPSec (Internet Protocol Security)
– RFCs 4301 y 4309…
• MPLS (Multi-Protocol Label Switching)
– RFC 3031 (1998 )…
• HTTP Tunneling
• Secure shell tunneling
6
Virtual Networks and Tunnels
7
Two separate private networks
8
Two virtual private networks sharing
common switches
9
A tunnel through an internetwork
10
ATM
Asynchronous Transfer
Mode
11
??? Virtual circuit network
12
ATM
• ATM is a connection-oriented, packet-switched
technology, which is to say, it uses virtual circuits.
• In addition to discovering a suitable route across an
ATM network, connection setup phase is also
responsible for allocating resources at the switches
along the circuit.
• This is done in an effort to ensure the circuit a
particular Quality Of Service.
• Indeed, the QoS capabilities of ATM are one of its
greatest strengths.
13
Quality Of Service requirement
14
ATM
• One thing that makes ATM really unusual is
that the packets that are switched in an ATM
network are of fixed length.
• To distinguish these fixed-length packets from
the more common variable-length packets
normally used in computer networks, they are
given a special name: cells.
• ATM may be thought of as the canonical
example of cell switching.
15
ATM cell format
• Generic Flow Control (GFC). These bits have not been widely used.
• The next 24 bits contain an 8-bit Virtual Path Identifier (VPI) and a 16bit Virtual Circuit Identifier (VCI). Is adequate to think of them as a
single 24-bit identifier that is used to identify a virtual connection.
• Following the VPI/VCI is a 3-bit Type field that has eight possible values.
Four of them, when the first bit in the field is set, relate to management
functions.
• Cell Loss Priority (CLP); a user or network element may set this bit to
indicate cells that should be dropped preferentially in the event of overload.
• The last byte of the header is an 8-bit CRC, known as the header error
check (HEC).
16
Example of a virtual path
• ATM uses a 24-bit identifier for virtual circuits. The one twist
is that the 24-bit identifier is split into two parts: an 8-bit
virtual path identifier (VPI) and a 16-bit virtual circuit
identifier (VCI). This effectively creates a two-level
hierarchy of virtual connections.
17
ATM: example
18
MPLS
Multiprotocol Label Switching
19
MPLS
• Originally viewed as a way to improve the
performance of the Internet.
• Tries to combine some of the properties of virtual
circuits with the flexibility and robustness of
datagrams.
• MPLS is very much associated with the Internet
Protocol’s datagram-based architecture—it relies on
IP addresses and IP routing protocols to do its job.
• MPLS-enabled routers also forward packets by
examining relatively short, fixed-length labels, and
these labels have local scope, just like in a virtual
circuit network.
20
MPLS
• It is perhaps this marriage of two seemingly opposed
technologies that has caused MPLS to have a somewhat
mixed reception in the Internet engineering community.
21
“What is it good for?”
•
•
•
To enable IP capabilities on devices that do not
have the capability to forward IP datagrams in the
normal manner (e.g. ATM switches).
To forward IP packets along “explicit routes”—
precalculated routes that don’t necessarily match
those that normal IP routing protocols would
select.
To support certain types of virtual private
network services.
22
MPLS provides these beneficial
applications
•
•
•
•
Virtual Private Networking (VPN).
Traffic Engineering (TE).
Quality of Service (QoS).
Any Transport over MPLS (AToM).
• Additionally, it decreases the forwarding overhead
on the core routers.
• MPLS technologies are applicable to any
network layer protocol.
23
MPLS
Label Swapping
Label Pop
Label push
LIB
Incoming
IF1
L1
Outgoing
IF2
L2
24
MPLS
IP
IP
IP Forwarding
#L1
IP
#L2
LABEL SWITCHING
IP
#L3
IP
IP Forwarding
25
Destination-Based Forwarding
Example network…
26
R2 allocates labels and advertises
bindings to R1…
This advertisement is carried in the “Label Distribution Protocol.” (LDP)
27
R1 stores the received labels in a
table…
28
R3 advertises another binding, and R2 stores the
received label in a table…
R1: Label Edge Router (LER), performs a complete IP lookup on arriving IP packets, and then
applies labels to them as a result of the lookup.
R2: label switching routers (LSRs), devices that run IP control protocols but use the label switching
forwarding algorithm
29
Label switching forwarding algorithm
IP
LAN
LAN
MPLS
Analiza
Etiqueta
Router IP
Analiza
Etiqueta
LSR
IP
LSR
P
LS
Edge
LSR
IP
Edge
LSR
IP
Etiqueta
Introduce (push)
Etiqueta
Extrae (pop)
Etiqueta
LSR
Analiza
Etiqueta
LSR
Analiza
Etiqueta
30
Label switching forwarding algorithm
Las etiquetas tienen significado
local; no tiene significado global
IP
Interfaz
Etiqueta
Interfaz Etiqueta
de entrada de entrada de salida de salida
IP
2
3
34
71
4
4
swap
17
77
LAN
LAN
MPLS
LSR
LSR
2
1
FEC Interfaz Etiqueta
de salida de salida
a
2
70
b
2
23
2
1
IP
70
23
IP 80
4
34
80
2
2
3
LSR
3
4
IP
34
Interfaz
Etiqueta
Interfaz Etiqueta
de entrada de entrada de salida de salida
1
1
IP
I P 4 17
3 77
1
2
3
IP 1
Edge
70
IP
LSR
23
2
1
IP 71
Router IP
Edge
LSR
3
IP
IP
3
1
LSR
Interfaz
Etiqueta
Interfaz Etiqueta
de entrada de entrada de salida de salida
1
80
2
71
31
Label switching forwarding algorithm
• We have replaced the normal IP destination address lookup
with a label lookup.
• IP prefixes are of variable length, and the IP destination
address lookup algorithm needs to find the longest match—
the longest prefix that matches the high- order bits in the IP
address of the packet being forwarded.
• By contrast, the label forwarding mechanism just described is
an exact match algorithm.
• Note that the routing algorithm can be any standard IP
routing algorithm (e.g., OSPF).
• The path that a packet will follow in this environment is the
exact same path that it would have followed if MPLS were
not involved—the path chosen by the IP routing algorithms.
• All that has changed is the forwarding algorithm.
32
Label Distribution Protocol (LDP)
• RFC 3036.
• The Label Distribution Protocol (LDP) is used to
establish MPLS transport LSPs when traffic
engineering is not required.
• It establishes LSPs that follow the existing IP
routing table, and is particularly well suited for
establishing a full mesh of LSPs between all of the
routers on the network.
• LDP can operate in many modes to suit different
requirements; however the most common usage is
unsolicited mode, which sets up a full mesh of
tunnels between routers.
33
Labels are “attached” to packets, but where
exactly are they attached?
a. Label on an ATM-encapsulated packet.
b. Label on a frame-encapsulated packet.
34
Label
35
What layer is MPLS?
• Since the MPLS header is normally found between
the layer 3 and the layer 2 headers in a packet, it is
some-times referred to as a layer 2.5 protocol.
36
Position of MPLS label
37
Forwarding Equivalence Class
LSR
LER
LSR
LER
LSP
IP1
IP1
IP1
#L1
IP1
#L2
IP1
#L3
IP2
#L1
IP2
#L2
IP2
#L3
IP2
IP2
• FEC is a group of packets which are forwarded in the same manner,
over the same path, and with the same forwarding treatment.
• An FEC might correspond to a destination IP subnet, but it also might
correspond to any traffic class that the Edge-LSR (LER) considers
significant. For example, all traffic with a certain value of IP precedence
might constitute a FEC.
• Thus, a FEC tends to correspond to a label switched path (LSP). The
reverse is not true, however: an LSP may be (and usually is) used for
multiple FECs.
38
Forwarding Equivalence Class
• It is possible for each flow to have its own set of labels through the
subnet. However, it is more common for routers to group multiple
flows and use a single label for them.
• The flows that are grouped together under a single label are said to
belong to the same FEC. This class covers not only where the
packets are going, but also their service class (in the differentiated
services sense) because all their packets are treated the same way
for forwarding purposes.
• A FEC is not a packet, nor is it a label. A FEC is a logical entity
created by the router to represent a class (category) of packets.
• When a packet arrives at the ingress router of an MPLS domain,
the router parses the packet's headers, and checks to see if the packet
matches a known FEC (class).
• Once the matching FEC is determined, the path and outgoing label
assigned to that FEC are used to forward the packet.
39
Forwarding Equivalence Classes
• Destination unicast address.
• Traffic Engineering.
• VPN.
• QoS (Quality of Service).
• Etc…
40
Enable IP capabilities on devices
that do not have the capability to
forward IP datagrams
• LSR, Label Switching Routers, devices that run IP
control protocols but use the label switching
forwarding algorithm.
• The major effect of changing the forwarding
algorithm is that devices that normally don’t know
how to forward IP packets can be used in an
MPLS network.
• The most notable early application of this result was
to ATM switches, which can support MPLS without
any changes to their forwarding hardware.
41
Multiprotocol Label Switching
• Because the MPLS headers are not part of the
network layer packet or the data link layer frame,
MPLS is to a large extent independent of both
layers.
• This property means it is possible to build MPLS
switches that can forward both IP packets and
ATM cells, depending on what shows up.
• This feature is where the ''multiprotocol'' in the
name MPLS came from.
42
(a) Routers connect to each other using an “overlay”of
virtual circuits. (b) Routers peer directly with LSRs
ATM switches
MPLS-Enabled switches
43
Explicit Routing
• IP has a source routing option, but it is not widely
used for several reasons, including the fact that only a
limited number of hops can be specified, and because
it is usually processed outside the “fast path” on
most routers.
• MPLS provides a convenient way to add capabilities
similar to source routing to IP networks, although
the capability is more often called “explicit routing”
rather than “source routing.”
44
A network requiring explicit routing
R1
R2
R7: R1-R3-R6-R7
R7: R2-R3-R4-R5-R7
• We can’t use the same procedures to distribute labels because those
procedures establish labels that cause packets to follow the normal paths
picked by IP routing.
• A new mechanism is needed. It turns out that the protocol used for this
task is the Resource Reservation Protocol (RSVP).
• But for now it suffices to say that it is possible to send an RSVP message
along an explicitly specified path (e.g., R1-R3-R6-R7) and use it to set up
label forwarding table entries all along that path. This is very similar to
the process of establishing a virtual circuit.
45
Explicit Routing
• One of the applications of explicit routing is “traffic
engineering,” which refers to the task of ensuring that
sufficient resources are available in a network to meet the
demands placed on it.
• Explicit routing can also help to make networks more resilient
in the face of failure, using a capability called fast reroute. It
is actually a feature of Resource Reservation Protocol Traffic Engineering (RSVP-TE) (RFC 5151).
• Explicit routes need not be calculated by a network operator.
There are a range of algorithms that routers can use to
calculate explicit routes automatically. The most common of
these is called constrained shortest path first (CSPF), which
is like the link-state algorithms, but which also takes
“constraints” into account.
46
ReSerVation Protocol with Traffic
Engineering (RSVP-TE)
• RSVP-TE is an extension of the resource reservation
protocol (RSVP) for traffic engineering.
• It supports the reservation of resources across an IP
network. Applications running on IP end systems can
use RSVP to indicate to other nodes the nature
(bandwidth, jitter, maximum burst, and so forth) of
the packet streams they want to receive.
• RSVP-TE is detailed in RFC 5151. RSVP-TE
generally allows the establishment of MPLS label
switched paths (LSPs), taking into consideration
network constraint parameters such as available
bandwidth and explicit hops.
47
ReSerVation Protocol with Traffic
Engineering (RSVP-TE)
• RSVP allows the use of source routing where the ingress
router determines the complete path through the
network.
• The ingress router can use a Constrained Shortest Path
First (CSPF) calculator to determine a path to the
destination, ensuring that any QoS requirements are met.
The resulting path is then used to establish the LSP.
• Operational overhead of RSVP-TE compared to the more
widely deployed label distribution protocol (LDP) will
generally be higher.
• This is a classic trade-off between complexity and
optimality in the use of technologies in
telecommunications networks.
48
Fast ReRoute (FRR)
• For example, it is possible to precalculate a path from
router A to router B that explicitly avoids a certain link L.
• In the event that link L fails, router A could send all
traffic destined to B down the precalculated path.
• The combination of precalculation of the “backup path”
and the explicit routing of packets along the path means
that A doesn’t need to wait for routing protocol packets
to make their way across the network or for routing
algorithms to be executed by various other nodes in the
network.
• In certain circumstances, this can significantly reduce the
time taken to reroute packets around a point of failure.
49
Fast ReRoute operation
Primary path (LSP) from A to E via B and D. The traffic of
customers connected to A and E will take this path in the normal
operation.
Secondary path (LSP) from A to E via C. For the primary LSP,
FRR (Fast ReRoute) is enabled. Once enabled, the other network
elements on the LSP will know that FRR is enabled.
1) There is a break between D and E. D will immediately know this and it will inform B and A.
For A to know that there is a failure between D and E, it takes a while.
2) Since D gets to know immediately about the failure and FRR is enabled on the LSP, it uses
the detour path D-C-E to get rid of the failure immediately and traffic will continue to flow
along that path. This takes less than 50ms.
3) Once the secondary LSP is up, traffic is switched to the secondary LSP and detour path is
turned down.
50
QoS and MPLS
• As was seen before, traffic is aggregated into
groups called FEC (Forwarding Equivalence
Classes) and these groups or behavior aggregates
are assigned to specific Label Switched Path
(LSP).
• Then traffic engineering can be implemented to
assign high-priority FECs onto high-quality
LSPs and lower-priority FECs onto lowerquality LSPs.
• This way QoS is implemented using MPLS.
51
QoS and MPLS
Usuario A
Tarifa premium
A
α
-
β
5
δ
-
γ
3
B
γ
α
Los routers X y Z se
encargan de etiquetar los
flujos según origen-destino
β
Y
4
β
α
4
β
-
γ
7
β
-
4
α
Z
X
Usuario B
Tarifa normal
5
α
5
β
α
δ
α
3
α
3
7
2
V
β
β
α
W
2
α
2
β
C
Usuario C
γ
β
β
7
C ha de distinguir de
algun modo los paquetes
que envía hacia A o B
(puede usar
subinterfaces diferentes)
52
MPLS “layer 2” VPN
• In this type of VPN, MPLS is used to tunnel layer 2 data
(such as Ethernet frames or ATM cells) across a network
of MPLS-enabled routers.
• One reason for tunnels is to provide some sort of network
service that is not supported by some routers in the
network.
• The same logic applies here: IP routers are not ATM
switches, so you cannot provide an ATM virtual circuit
service across a network of conventional routers.
However, if you had a pair of routers interconnected by a
tunnel, they could send ATM cells across the tunnel and
emulate an ATM circuit.
• The term for this technique within the IETF is
pseudowire emulation.
53
ATM circuit emulated by a tunnel
MPLS-enabled routers
• The head router needs to be configured with the incoming
port, the incoming VCI, the “demultiplexing label” for this
emulated circuit, and the address of the tunnel end router.
• The tail end router needs to be configured with the outgoing
port, the outgoing VCI, and the demultiplexing label.
54
Forwarding ATM cells along a tunnel
1. An ATM cell arrives on the designated input port with the appropriate VCI value (101 in
this example).
2. The head router attaches the demultiplexing label that identifies the emulated circuit.
3. The head router then attaches a second label, which is the tunnel label that will get the
packet to the tail router.
4. Routers between the head and tail forward the packet using only the tunnel label.
5. The tail router removes the tunnel label, finds the demultiplexing label, and recognizes the
emulated circuit.
6. The tail router modifies the ATM VCI to the correct value (202 in this case) and sends it out
the correct port.
55
MPLS labels may be “stacked”
• In this example the packet has two labels attached to
it. This is one of the interesting features of MPLS—
labels may be “stacked” on a packet to any depth.
This provides some useful scaling capabilities.
• In this example, it enables a single tunnel to carry a
potentially large number of emulated circuits.
• The same techniques described here can be applied to
emulate many other layer 2 services, including
Frame Relay and Ethernet.
• Virtually identical capabilities can be provided using
IP tunnels; the main advantage of MPLS here is the
shorter tunnel header.
56
Label stacking
• Label: Label Value, 20 bits.
• Exp: Experimental Use, 3 bits.
• S: Bottom of Stack, 1 bit.
• TTL: Time to Live, 8 bits.
57
Label stacking
IP
PE
IP
PE
41
IP
P
P
IP
LS
P
P
91
1
PE
P
IP
IP
31
P
2
1
3
1
P2
LS
2IP
4 IP
2
3 IP
P
LS
IP
72
1
91
70
2
72
70
1
3
P
72
91
1
17
17
2 IP
2
P1
LS
IP 81
3
PE
IP 27
IP
72
91
IP 61
P
IP 25
4
1
PE
P
IP
LS
P
2
PE
IP
LSP
LSP1
LSP2
Túnel
58
MPLS layer 3 VPN
• The details of layer 3 VPNs are quite complex. Represent
one of the most popular uses of MPLS.
• Use stacks of MPLS labels to tunnel packets across an
IP network. However, the packets that are tunneled are
themselves IP packets —hence the name “layer 3
VPNs.”
• In a layer 3 VPN, a single service provider operates a
network of MPLS-enabled routers and provides a
“virtually private” IP network service to any number of
distinct customers.
• Each customer of the provider has some number of sites,
and the service provider creates the illusion for each
customer that there are no other customers on the
network.
59
MPLS layer 3 VPN
• The customer sees an IP network interconnecting his
own sites, and no other sites. This means that each
customer is isolated from all other customers in
terms of both routing and addressing.
• Customer A can’t send packets directly to customer
B, and vice versa. Customer A can even use IP
addresses that have also been used by customer B. As
in layer 2 VPNs, MPLS is used to tunnel packets
from one site to another.
• The configuration of the tunnels is performed
automatically by some fairly elaborate use of BGP
(BGP/MPLS VPNs RFC 2547).
60
Layer 3 VPN. Customers A and B each obtain a
virtually private IP service from a single provider
61
LDP for MPLS Services
• The Label Distribution Protocol (LDP) is used to
establish MPLS transport LSPs when traffic
engineering is not required.
• It establishes LSPs that follow the existing IP
routing table, and is particularly well suited for
establishing a full mesh of LSPs between all of the
routers on the network.
• LDP can operate in many modes to suit different
requirements; however the most common usage is
unsolicited mode, which sets up a full mesh of
tunnels between routers.
62
LDP vs. RSVP-TE
• “Which signaling protocol to use – LDP or RSVP-TE?”.
• The traditional response is “Use LDP when you want
simplicity, use RSVP-TE when you want bandwidth
guarantees and 50ms reroute around failure”.
• Why not both? - LDP over RSVP-TE (LDPoRSVP-TE).
63
LDP vs. RSVP-TE
• The main advantage of LDP over RSVP
is the ease of setting up a full mesh of
tunnels using unsolicited mode.
• So it is most often used in this mode to
set up the underlying mesh of tunnels
needed by Layer 2 and Layer 3 VPNs.
64
MPLS. Ejercicio
Assume that it takes 32 bits to carry each MPLS label that is
added to a packet when the “shim” header is used.
a) How many additional bytes are needed to tunnel a packet
using the MPLS techniques?
b) How many additional bytes are needed, at a minimum, to
tunnel a packet using an additional IP header (IP/IP)?
c) Calculate the efficiency of bandwidth usage for each of
the two tunneling approaches when the average packet
size is 300 bytes. Repeat for 64-byte packets. Bandwidth
efficiency is defined as (payload bytes carried)÷(total
bytes carried).
65
MPLS Terms
LSP
FECs
α
-
β
5
δ
-
γ
3
δ
α
γ 3
X
B
5
β
4
β
α
5
β
α
A
no MPLS
enabled
LIB
4
Y
α
β 2 α W
V
α
4
β
-
γ
7
β
-
α
no MPLS enabled
β
C
Z
7
β
LIB
LER
α
γ
LIB
3
MPLS
Multiple Protocol Label Switching
LER
Label Edge Router
LSR
Label Switch Router
LIB
Label Information Base
LSP
Label Switch Path
FEC
Forward Equivalence Class
β
2
α
2
β
7
LER
LSR (V, W, Y)
LSRs X, Y, Z, V, W: MPLS enabled.
66
MPLS
Anexo opcional
67
Behavior of TTL
68
Propagation behavior of TTL between IP
header and MPLS labels
69
TTL propagation in label-to-label operation in
the case of a swap, push, and pop operation
70
ICMP "Time Exceeded" sent by a router in an
MPLS network
71
Ejemplo de MPLS
72
Ejemplo de MPLS
• En este ejemplo se quiere
comunicar el router (no
MPLS) que se encuentra en
la parte superior y el router
(no MPLS) que se encuentra
en la parte inferior a través
de la red MPLS
• Las tablas muestran la
asociación de las
direcciones de red con las
parejas interfaz-etiqueta de
salida y de entrada.
73
Ejemplo de MPLS
• Paso 1: Vemos la tabla del router
externo que está conectado a dos
redes de clase C.
La flecha azul claro indica que el
router externo comunica al LSR
frontera las rutas que posee (a
través del protocolo que sea). Es
el ‘routing update’.
74
Ejemplo de MPLS
• Paso 2: El LSR elige una etiqueta
no usada mediante LDP (la 5 por
ejemplo).
Así un paquete que llegue por el
Serial1 con la etiqueta 5 será
enviada por el Serial0 sin
etiqueta.
La flecha roja indica que se
comunica el uso de la etiqueta 5
al siguiente LSR .
75
Ejemplo de MPLS
• Paso 3: El siguiente LSR almacena
la etiqueta 5 (como etiqueta de
salida) en su LIB asociada con la
Serial0.
Escoge la etiqueta 17 (como
etiqueta de entrada) y la asocia
con el Serial1 y lo propaga al
siguiente LSR vía LDP.
De este modo los paquetes que
lleguen por el Serial1 con la
etiqueta 17 se enviaran por la
Serial0 con la etiqueta 5.
76
Ejemplo de MPLS
• Pasos 4 y 5: Se procede de forma
similar a los anteriores pasos.
La tabla del paso 4 es más grande
porque se actualiza con
información del LSR de la
derecha.
La tabla del LSR frontera (paso 5)
solo tiene etiquetas de salida
porque esta conectado al router
no-MPLS emisor.
El LSP establecido queda
señalado con la flecha azul
marino.
77
Ejemplo de MPLS
• Paso 6: El LSR frontera envía
información de routing al router
externo.
Éste actualiza sus tablas de
routing, de modo que para enviar
paquetes a las redes de clase C
del router de la parte inferior, lo
hará a través del Serial0.
78
Ejemplo de MPLS
• Pasos 7 y 8: El LSR frontera del
fondo también propaga la
información de routing al LSR que
tiene conectado por el Serial2.
Éste actúa de forma similar y
propaga la información al otro
LSR.
Se supone que se seguiría
propagando por todos los LSR
79
Ejemplo de MPLS
• Paso 9: El LSR recibe información
de routing del LSR de la izquierda
y actualiza su tabla LIB.
• Podemos observar el
comportamiento multipunto del
MPLS en el LSR del paso 4 ya que
todos los paquetes que entran
son etiquetados con la misma
etiqueta (17) y enviados por el
Serial0.
80