Transcript VPLS - DSPCSP

PWE + VPLS
Yaakov (J) Stein
June 2006
Chief Scientist
RAD Data Communications
Contents

Interworking

VPNs

PWs

TDM PWs

Ethernet PWs

Other PWs

PWE control protocol

L2VPNs

LDP vs. BGP

Provisioning VPLS

Generalizations

L3VPNs
Y(J)S PWE-VPLS Slide 2
Interworking
Y(J)S PWE-VPLS Slide 3
Tunneling - interworking
mating different network protocols is called interworking
protocol converter goes by various names :
– interworking function (IWF)
– gateway (GW)
simplest case is network interworking
easily provided by tunneling
native
network
infrastructure
network
native
network
Y(J)S PWE-VPLS Slide 4
Tunneling - provider networks
users traditionally have private networks
they interconnect their sites using leased lines
– no contention with outside users
– guaranteed privacy
– complex and costly maintenance
customer
network
leased line
customer
network
service providers (SPs) can provide virtual private networks
provided by (once again by) tunneling edge-to-edge
Y(J)S PWE-VPLS Slide 5
Basic emulation by tunneling
customer
network
physical link
customer
network
end to end
edge to edge
provider
network
customer
network
customer
network
emulated link
provider network edge
provider network edge
Y(J)S PWE-VPLS Slide 6
Interworking motivation
there are many different types of network traffic (voice, video, file-xfer, etc)
all types fall into one of three classes:
– Real-time constant bit-rate
– Real-time variable bit-rate
– Non-real-time (packet)
there are many different types of network (IP,ATM,FR,Eth,etc)
most were originally designed for a specific type of traffic
providers with one type of network infrastructure want to fully exploit it
they desire to carry all types of network traffic
Y(J)S PWE-VPLS Slide 7
Service Interworking
Service interworking:
direct conversion between 2 native service formats
Native
Service
A
service
interworking
function
Native
Service
B
Y(J)S PWE-VPLS Slide 8
VPNs
Y(J)S PWE-VPLS Slide 9
Conventional Ethernet-IP model
Ethernet
IP
Ethernet
conventional model:

Ethernet is a LAN technology
– last 100m
– 10s of hosts

IP is a WAN technology
– data transported in native IP
– different L2 technologies for last segment
modern Ethernet wants to be more
Y(J)S PWE-VPLS Slide 10
Virtual Private Networks
service
provider
network
SPs want to offer customers site interconnect service
since the private networks are interconnected over
a public PSN
this results in a Virtual Private Network
unlike the traditional WAN architecture
the entire native packet/frame must be tunneled
Example: Transparent LAN Service (TLS)
Y(J)S PWE-VPLS Slide 11
Basic (L2,L3)VPN model
physical link
customer
network
customer
network
emulated link
customer
network
Customer
Edge
(CE)
Provider
Provider
provider Edge
Edge
network
(PE)
(PE)
AC = Attachment Circuit
Customer
Edge
customer
network
(CE)
AC = Attachment Circuit
provider network may be L3 (e.g. IP) or L2 (e.g. Ethernet)
Y(J)S PWE-VPLS Slide 12
(L2,L3)VPN in more detail
C
C
C
C
CE
CE
C
C
customer 1 network
P
P
P
C
C
customer 2 network
P
provider network
CE
C
CE
P
PE
customer 2 network
PE
PE
C
P
C
C
CE
C
Key
Customer router/switch
Customer Edge router/switch customer 1 network
Provider router/switch
Provider Edge router/switch
Y(J)S PWE-VPLS Slide 13
L3 encapsulation
for simplicity, let’s think of an IP network :
the traditional architecture uses the following packet formats:
WAN
Eth hdr IP hdr payload Eth FCS
Eth hdr IP hdr payload Eth FCS
WAN L2 hdr IP hdr payload
a VPN model (Ether-IP) uses the following packet formats:
WAN
Eth hdr IP hdr payload Eth FCS
Eth hdr IP hdr payload Eth FCS
WAN L2 hdr IP hdr Eth hdr IP hdr payload Eth FCS*
Y(J)S PWE-VPLS Slide 14
VPN Challenges
192.115.243.79
192.115.243.19
SP
network
192.115.243.19
Security
Private IP addresses
Multiple higher-layer protocols
SP resource requirements
Complex provider - customer relationship
Y(J)S PWE-VPLS Slide 15
MPLS solves IP address problem
192.115.243.19
1
2
MPLS
network
1
192.115.243.19
MPLS label
IP header
payload
assume customers 1 and 2 use overlapping IP addresses
then C-routers have inconsistent tables
ingress PE-router pushes a label
P-routers see only MPLS label
P-routers don’t see IP addresses - no ambiguity
P-routers see only the MPLS label - not LAN IP addresses
PE routers know how to map CE LANs
Y(J)S PWE-VPLS Slide 16
VPN types

Legacy
– proprietary leased-line (not virtual)
– Frame Relay over E1/T1
– ATM over E1 or multiple-E1

Pure IP
– IPSec tunnel
– L2TP tunnel

MPLS L3VPN
– RFC4364 (ex 2547bis)

MPLS L2VPN
– VPWS / VPLS
Y(J)S PWE-VPLS Slide 17
Pseudowires
Pseudowire (PW): A mechanism that emulates the
essential attributes of a native service while transporting
over a packet switched network (PSN)
Y(J)S PWE-VPLS Slide 18
Pseudowires
Packet Switched Network (PSN)
– network that forwards packets
– IPv4, IPv6, MPLS, Ethernet (although IETF does not touch)
a pseudowire (PW) is a mechanism to tunnel through a PSN
PWs are bidirectional (unlike MPLS LSPs)
PW architecture is an extension of VPN architecture
Y(J)S PWE-VPLS Slide 19
Pseudowire Emulation
Edge to Edge
Customer
Edge
provider’s
PSN
(CE)
Customer
Edge
(CE)
Customer
Edge
(CE)
Customer
Edge
Provider
Edge
Provider
Edge
(CE)
(PE)
(PE)
Customer
Edge
native
service
PseudoWires
(PWs)
native
service
(CE)
Y(J)S PWE-VPLS Slide 20
Provider Network Architecture
provider network is composed of:
• Provider routers (P routers)
• Provider edge routers (PE routers)
P
router
P
router
native
service
PE
router
P
router
A tunnel may
contain
many PWs
PE
router
native
service
P
router
Y(J)S PWE-VPLS Slide 21
IETF PWE3 WG
In the Internet Area of the Internet Engineering Task Force
Native (layer 1,2) services :
 ATM (port mode, cell mode, AAL5-specific modes)
 FR
 Ethernet (DIX, 802.3, VLAN)
 TDM (SONET/SDH, E1, T1, E3, T3)

…
Supported Packet Switched Networks (PSNs)
 IPv4
 IPv6
 MPLS
 L2TPv3
 (not Ethernet …)
Y(J)S PWE-VPLS Slide 22
PWE3 WG Charter

Edge-to-edge emulation and maintenance of PWs
– tunnel creation and placement out of scope


Network interworking, not service interworking
Must not exert controls on underlying PSN
– but diffserv, RSVP-TE can be used

Use RTP when necessary
– for real-time functions, clock recovery

Realize that emulation will not be perfect
– need applicability statement for each native service

WG will produce the following documents
– requirements (RFC 3916), architecture (RFC 3985) documents
– control protocol definition
– service specific encapsulation documents for each native service
Y(J)S PWE-VPLS Slide 23
MPLS
Much of the PWE work is focused on MPLS

Emulated services have QoS and TE requirements
–
–
–
–

IP is basically a “best effort” service
diffserv and RSVP extensions not prevalent
MPLS can provide TE guarantees
RSVP-TE (CR-LDP) allows TE signaling
IP provides no standard “bundle” multiplexing method
–
–
–
–
–
Dictionary:
UDP/TCP ports provide application multiplexing
RTP uses ports in a nonstandard way
L2TP includes a multiplexing mechanism
MPLS label stack provides natural multiplexing method
Using “inner labels” provides two layers of switching (like ATM VP/VC)
MPLS-f inner label
outer label(s)
ITU-T interworking label transport label(s)
IETF
PW label
tunnel label(s)
Y(J)S PWE-VPLS Slide 24
Simple MPLS solution
CE
CE
ACs
CE
PE
P
CE
P
PE
ACs
CE
CE
each customer network mapped to pair of (unidirectional) LSPs
supports various AC technologies
each native packet/frame encapsulated with MPLS label
scaling problem:
 requires large number of LSPs
 P-routers need to be aware of customer networks
Y(J)S PWE-VPLS Slide 25
(Martini) Pseudowires
CE
CE
transport tunnel
ACs
CE
PE
ACs
PE
CE
CE
CE
PWs are bidirectional
transport MPLS tunnel set up between PEs
multiple PWs may be set up inside tunnel
MPLS (outer) label
PW (inner) label
payload
Native packet/frame encapsulated with 2 labels
P-routers are unaware of individual customer networks
Y(J)S PWE-VPLS Slide 26
PWE packet format
PSN / multiplexing
optional RTP header
optional control word (CW)
higher layers
payload
Y(J)S PWE-VPLS Slide 27
Example formats
MPLS PSN
tunnel
label(s)
PW
label
control
word
Payload
L2TPv3 PSN
IP header
(5*4 B)
session ID (4 B)
optional cookie (4 or 8 B)
control word (4 B)
payload
Y(J)S PWE-VPLS Slide 28
PWE Control Word
0000
flags FRG Length
Sequence Number
0000
– Identifies packet as PW (not IP)
– used to ensure ECMP mechanisms don’t interfere with proper functioning
– 0001 for PWE OAM (VCCV)
Flags (4 b)
– not all encapsulation define
– used to transport native service fault indications
FRG
– may be used to indicate payload fragmentation
 00 = unfragmented
01 = 1st fragment
 10 = last fragment
11 = intermediate fragment
Length (6 b)
– used when packet may be padded by L2
Sequence Number (16 b)
– used to detect packet loss / misordering
Y(J)S PWE-VPLS Slide 29
Other Standards Bodies

ITU-T SG13
– Y.1411, Y.1412, Y.1413, Y.1414, Y.1415, Y.1452, Y.1453,
X.84

ITU-T SG15
– G.769, G.8261

MFA Forum (MPLS – Frame Relay – ATM)
– TDM over MPLS using AAL1 IA 4.0
– I.366.2 over MPLS IA 5.0
– af-aic-0178

MEF (Metro Ethernet Forum)
– MEF 8.0.0
Y(J)S PWE-VPLS Slide 30
TDM PWs
Y(J)S PWE-VPLS Slide 31
TDMoIP Protocol Processing
TDM
IP Packets
IP Packets
TDM
PSN
Steps in TDMoIP
 The synchronous bit stream is segmented
 The TDM segments are adapted
 TDMoIP control word is prepended
 PSN (IP/MPLS) headers are prepended (encapsulation)
 Packets are transported over PSN to destination
 PSN headers are utilized and stripped
 Control word is checked, utilized and stripped
 TDM stream is reconstituted (using adaptation) and played out
Y(J)S PWE-VPLS Slide 32
TDM Structure
handling of TDM depends on its structure
unstructured TDM (TDM = arbitrary stream of bits)
…
structured TDM
framed
S
Y
N
C
(8000 frames per second)
S
Y
N
C
channelized
SYNC
S
Y
N
C
(single byte timeslots)
TS2
TS1
(1 byte)
TS3
…
signaling
bits
…
TSn
multiframed
frame
frame
frame
…
multiframe
frame
Y(J)S PWE-VPLS Slide 33
TDM transport types
Structure-agnostic transport (SAToP – RFC4553)
• for unstructured TDM
• even if there is structure, we ignore it
• simplest way of making payload
• OK if network is well-engineered
Structure-aware transport (TDMoIP, CESoPSN)
• take TDM structure into account
• must decide which level of structure (frame, multiframe, …)
• can overcome PSN impairments (PDV, packet loss, etc)
Y(J)S PWE-VPLS Slide 34
Structure aware encapsulations
Structure-locked encapsulation (CESoPSN)
headers
TDM structure
TDM structure
TDM structure
TDM structure
Structure-indicated encapsulation (TDMoIP – AAL1 mode)
headers
AAL1 subframe AAL1 subframe AAL1 subframe
AAL1 subframe
Structure-reassembled encapsulation (TDMoIP – AAL2 mode)
headers
AAL2 minicell
AAL2 minicell
AAL2 minicell
AAL2 minicell
Y(J)S PWE-VPLS Slide 35
Ethernet PWs
Y(J)S PWE-VPLS Slide 36
Ethernet limitations
Ethernet LAN is the most popular LAN
but Ethernet can not be made into a WAN

Ethernet is limited in distance between stations

Ethernet is limited in number of stations on segment
Ethernet is inefficient in finding destination address
Ethernet only prunes network topology, does not route


so the architecture that has emerged is Ethernet private networks
connected by public networks of other types (e.g. IP)
LAN
LAN
WAN
Y(J)S PWE-VPLS Slide 37
Traditional WAN architecture
this model is sensible when traffic contains a given higher layer
Ethernet header is removed at ingress and a new header added at egress
this model is not transparent Ethernet LAN interconnect
 Ethernet LANs with multiple higher layer packet types
(e.g. IPv4, IPv6, IPX, SNA, CLNP, etc.) can’t be interconnected
 raw L2 Ethernet frames can not be sent
the Ethernet layer is terminated at WAN ingress
the traffic is no longer Ethernet at all
Ethernet
Ethernet
WAN
not Ethernet
Y(J)S PWE-VPLS Slide 38
Tunneling Ethernet frames
users with multiple sites want to connect their LANs
so that all locations appear to be on the same LAN
this requires tunneling of all Ethernet L2 frames (not only IP)
between one LAN and another
the entire Ethernet frame needs to be preserved
(except perhaps the FCS which can be regenerated at egress)
Ethernet
Ethernet
X
Ethernet inside X
Y(J)S PWE-VPLS Slide 39
Ethernet over
HDLC/FR/ATM/SONET/SDH/PDH
Ethernet frames can be carried over various WANs
HDLC: not standardized, Cisco-HDLC
FR: RFC2427 / STD0055 (ex 1490)
ATM: RFC2684 / (ex 1483), LANE
SONET/SDH/PDH: PoS (RFC 2615 ex RFC1619),
LAPS (X.85/X.86), GFP (G.7041 )
entire Ethernet frame (or IP packet) is used as payload
Y(J)S PWE-VPLS Slide 40
Ethernet PW (RFC 4448)
can transport tagged or untagged Ethernet frames
if tagged encapsulation can be “raw mode” or “tagged mode”
tagged mode processes SP tags
control word is optional
even if control word is used, sequence number if optional
standard mode – FCS is stripped and regenerated
FCS retention mode (not in 4448) allows retaining FCS
Y(J)S PWE-VPLS Slide 41
Ethernet Pseudowire packet (MPLS)
tunnel
label
PW
label
control
word
Ethernet Frame
Ethernet Frame usually has FCS stripped
SP tag may also be stripped
optional control word
generation and processing of sequence number is optional
0000
reserved
Sequence Number (16b)
Y(J)S PWE-VPLS Slide 42
Other PWs
Y(J)S PWE-VPLS Slide 43
What other PW clients are there?
ATM (4 different modes)
frame relay
SONET/SDH
HDLC / PPP
Fiber channel
X.25
Generic
????
Y(J)S PWE-VPLS Slide 44
PWE control protocol
Y(J)S PWE-VPLS Slide 45
PWE (Martini) control protocol

PWE control protocol (RFC 4447) used to set up / configure PWs

used only by PW end-points (PEs in standard model)
intermediate nodes (e.g. P routers) don’t participate or see
P
P
PE

based on LDP
–
–
–
–
PE
P
P
P
targeted LDP is used to communicate with opposite end-point
2 new FECs for PWs
new TLVs added for PW-specific functionality
associates two labels with PW
LDP will be discussed later
Y(J)S PWE-VPLS Slide 46
PWE control
a PW is a bidirectional entity (two LSPs in opposite directions)
a PW connects two forwarders
2 different LDP TLVs can be used
– PWid FEC (128)
– Generalized ID FEC (129)
FEC 128
– both end-points of PW must be provisioned with a unique (32b) value
– each PW end-point independently initiates LSP set up
– LSPs bound together into a single PW
FEC 129
– used when autodiscovering PW end-points
– each end-point has attachment identifier (AI) …
Y(J)S PWE-VPLS Slide 47
Generalized ID
for each forwarder we have a PE-unique Attachment Identifier (AI)
<PE, AI> must be globally unique
frequently useful to group a set of forwarders into a attachment group
where PWs may only be set up among members of a group
then Attachment Identifier (AI) consists of
– Attachment Group Identifier (AGI) (which is basically a VPN-id)
– Attachment Individual Identifier (AII)
the LSPs making up the (two directions of the) PW are
< PE1, (AGI, AII1), PE2, (AGI, AII2) > and
< PE2, (AGI, AII2), PE1, (AGI, AII1) >
we also need to define
– Source Attachment Identifier (SAI = AGI+SAII)
– Target Attachment Identifier (TAI = AGI+TAII)
receiving PE can map TAI uniquely to AC
Y(J)S PWE-VPLS Slide 48
PWE OAM
Y(J)S PWE-VPLS Slide 49
VCCV
VC (old name for PW) connectivity verification
runs inside PW (same PW label) as an associated channel
differentiated by control word format (PWACH – RFC 4385)
0001
VER
RES=0
Channel Type (0x21-IPv4 0x57-IPv6)
inside VCCV several different OAM mechanisms may be used:
– ICMP
– LSP ping
– BFD
– ???
Y(J)S PWE-VPLS Slide 50
Multisegment PW (MS-PW)
Y(J)S PWE-VPLS Slide 51
Multiple PSN domains
P
P
P
P
T-PE
S-PE
T-PE
P
P
P
P
P
P
Single-Segment PW (SS-PW) requires PEs to see each other
when multiple PSN domains this may not be the case
Terminal-PEs interconnect via stitching-PE
PW label becomes a true MPLS label (switching, swapping)
when more than one S-PE
need to ensure that the 2 LSPs traverse the same one
Y(J)S PWE-VPLS Slide 52
L2VPNs
Y(J)S PWE-VPLS Slide 53
VPWS
CE
AC
PE
PE
AC
CE
provider
network
Virtual Private Wire Service is a L2 point-to-point service
it emulates a wire supporting the Ethernet physical layer
set up MPLS tunnel between PEs
set up Ethernet PW inside tunnel
CEs appear to be connected by a single L2 circuit
(can also make VPWS for ATM, FR, etc.)
Y(J)S PWE-VPLS Slide 54
VPLS
AC
PE
CE
AC
CE
PE
for clarity only one VPN is shown
PE
AC
CE
VPLS emulates a LAN over an MPLS network
set up MPLS tunnel between every pair of PEs (full mesh)
set up Ethernet PW inside tunnels, for each VPN instance
CEs appear to be connected by a single LAN
PE must know where to send Ethernet frames …
but this is what an Ethernet bridge does
Y(J)S PWE-VPLS Slide 55
VPLS
V B
CE
CE
B V
V B
CE
a VPLS-enabled PE has, in addition to its MPLS functions:

VPLS code module (IETF drafts)

Bridging module (standard IEEE 802.1D learning bridge)
SP network
(inside rectangle)
looks like a single Ethernet bridge!
Note: if CE is a router, then PE only sees 1 MAC per customer location
Y(J)S PWE-VPLS Slide 56
VPLS bridge
PE maintains a separate bridging module for each VPN (VPLS instance)
VPLS bridging module must perform:
 MAC learning
 MAC aging
 flooding of unknown MAC frames
 replication (for unknown/multicast/broadcast frames)
unlike true bridge, Spanning Tree Protocol is not used
 limited traffic engineering capabilities
 scalability limitations
 slow convergence
forwarding loops are avoided by split horizon
 PE never forwards packet from MPLS network to another PE
 not a limitation since there is a full mesh of PWs
so always send directly to the right PE
Y(J)S PWE-VPLS Slide 57
Bridge - both ways
CE
V B
CE
CE
CE
CE
B V
CE
V B
a packet from a CE:
may be sent back to a CE
may be sent to a PE via a PW
CE
CE
a packet from a PE:
is only sent to a CE (split horizon)
is sent to a particular CE based on 802.1D bridging
Y(J)S PWE-VPLS Slide 58
VPLS code module
VPLS signaling
establish PWs between PEs per VPLS
VPLS autodiscovery
locates PEs participating in VPLS instance
obtain frame from bridge
encapsulate Ethernet frames
and inject packet into PW
retrieve packet from PW
removes PW encapsulation
and forward Ethernet frame to bridge
Y(J)S PWE-VPLS Slide 59
L2VPN vs. L3VPN
PE
CE
PE
CE
?
PE
CE
in L2VPN CEs appear to be connected by single L2 network
PEs are transparent to L3 routing protocols
CEs are routing peers
in L3VPN CE routers appear to be connected by a single L3 network
CE is routing peer of PE, not remote CE
PE maintains routing table for each VPN
Y(J)S PWE-VPLS Slide 60
IPLS (IP-only LAN Service)
mechanisms may be simplified if Ethernet frames carry only IP traffic
enables upgrade of IP routers to support VPLS-like services
in this case CE devices are routers, not switches
frames are still forwarded based on MAC DA (not L3VPN)
but MAC forwarding tables updated via PW signaling, not 802.1D
PE snoops IP and ARP frames to discover CEs connected to it
creates (AC,VPN-ID,IP-addr,MAC-addr) entry
creates PWs to all PEs participating in VPN-ID
sends entries to these PEs
Address Resolution Protocol (ARP) messages are proxied
rather than being carried transparently
PE searches entries it has received
can support different AC types (Ethernet and FR)
ARP Mediation ensures proper mapping
Y(J)S PWE-VPLS Slide 61
LDP vs. BGP
Y(J)S PWE-VPLS Slide 62
LDP vs. BGP
both use TCP for reliable transport (LDP uses UDP for hellos)
both are hard-state protocols
both use TLV format for parameters
BGP
LDP
multiprotocol (IPv4, IPv6, IPX, MPLS)
MPLS only
highly complex protocol
simpler protocol
provides routing / label distribution
only label distribution
built-in autodiscovery mechanism
extendable for autodiscovery
Y(J)S PWE-VPLS Slide 63
BGP
header (19B)
marker
(16B)
length
(2B)
marker can be used for authentication
type
(1B)
data
(variable)
(TCP MD5 signature)
length is total BGP PDU length, including header
type
–
–
–
–
OPEN (for session initialization)
UPDATE (add, change and withdraw routes)
NOTIFICATION (return error messages, terminate session)
KEEPALIVE (heartbeat)
KEEPALIVE packet consists of 19B header only
Y(J)S PWE-VPLS Slide 64
BGP state machine

idle – no session (awaiting session initialization)

connect – attempting to connect to peer

active – started TCP 3-way handshake (router busy)

open sent – have sent OPEN message

open confirm – after receiving TCP SYN for OPEN message

established – BGP session up and running
Y(J)S PWE-VPLS Slide 65
BGP OPEN
version
(1B)
my AS
(2B)
hold time
(2B)
BGP-ID
(2B)
op len
(1B)
opt parameters
(variable)
version (3 or 4)
my AS – identifier of autonomous system
hold time – max time (sec) between receipt of messages
BGP ID – sender’s BGP identifier
op len – length (bytes) of optional parameters
opt parameters - TLVs
Y(J)S PWE-VPLS Slide 66
BGP UPDATE
WR len withdrawn
routes
(2B)
(var)
PA len
(2B)
path
attributes
(var)
Withdrawn Routes – list of routes no longer to be used
NLRI
(var)
(NLRI format- see below)
Path Attributes – route specific information (see next page)
Network Layer Reachability Information – (classless) routing information
len
(1B)
prefix
(variable)
the NLRI is a list of address-prefixes
each prefix must be masked from the left to the length specified
Y(J)S PWE-VPLS Slide 67
BGP UPDATE - Path Attributes
flags
(1B)
type code
(1B)
flags
O – optional/well-known bit
if 1 must be recognized by all BGP implementations
if W=1 and unrecognized attribute, BGP sends notification and session closed
T – transitive/nontransitive bit
if 1 and attribute unrecognized it is passed along, else silently ignored
well-known attributes are always transitive
C – complete/partial bit
L – attribute length bit
(for optional transitive attributes only)
(=0 attribute length is 1B, =1 length is 2B)
type code
ORIGIN, AS_PATH, NEXT_HOP, MED, LOCAL_PREF,
AGGREGATOR, COMMUNITY, ORIGINATOR_ID…
Y(J)S PWE-VPLS Slide 68
BGP NOTIFICATON
error
code
(1B)
error
subcode
(2B)
data
(var)
all notification messages cause BGP session to close
error codes include:
–
–
–
–
–
–
message header error
open message error
update message error
hold timer expired
state machine error
other fatal error
Y(J)S PWE-VPLS Slide 69
LDP
header (10B)
version
(2B)
length
(2B)
LDP-ID
(6B)
messages
(variable)
version – presently 1
length - PDU length, excluding version and length fields
LDP-ID – identifies label space of sending LDP peer
– LSR-ID(4B) globally unique LSR ID
– label space ID (2B) for per-port label spaces
(zero for per-platform label spaces)
messages – zero or more TLVs (see next page)
Y(J)S PWE-VPLS Slide 70
LDP messages
type
(2B)
length
(2B)
message-ID
(4B)
mandatory
parameters
(variable)
optional
parameters
(variable)
type U
message code
U – unknown message bit
if message type unknown to receiver
U=0 – receiver returns notification to sender
U=1 – receiver silently ignores
length - message length, excluding type and length fields
Message-ID – unique ID for message (for matching with returned notification)
if there are mandatory parameters, they most appear in a specific order
optional parameters may appear in any order
Y(J)S PWE-VPLS Slide 71
LDP message types
Hello (UDP, for discovery)
Initialization (specifies LDP version, label space range, parameters)
KeepAlive (heart beat)
Notification (error, e.g.unsupported version, unknown/malformed msg, timer expired)
Address (LSR advertises its interface IP address(es) to peers)
Address Withdraw (LSR revokes previously advertised interface IP address)
Label Mapping (downstream LSR advertisement of a label mapping for a FEC )
Label Withdraw (downstream LSR informing that binding is revoked)
Label Request (upstream LSR request for binding in downstream-on-demand mode)
Label Release (upstream LSR informing that binding no longer needed)
Label Abort Request (upstream LSR asks to revoke request before satisfied)
Y(J)S PWE-VPLS Slide 72
LDP state machine

LSR periodically transmits hello UDP messages
– multicast to “all routers on subnet” group
– targeted to preconfigured IP address

LSRs listen on this UDP port for hello messages

when LSR receives hello from another LSR
– it opens a TCP connection to that other LSR
or (for extended discovery)
– it unicast transmits a hello back to the other LSR

LSR with higher ID sends session initialization message

other LSR LDP accepts (sends keepalive) or rejects

informative or keepalive messages sent
3.2
Y(J)S PWE-VPLS Slide 73
Provisioning VPLS
Y(J)S PWE-VPLS Slide 74
Provisioning
customers may want their SP to take an active role
in managing their networks
Provider Provisioned VPN (PPVPN) refers to VPN
for which SP participates in management and provisioning
by provisioning we mean (at least) :
 setting up the ACs (often manual configuration)
 assigning global VPN-ID to VPN instances
 discovery of all PEs that participate in a VPN instance
 associating AC with VPN at PE
 providing PEs with information needed to set up tunnels
 configuring tunnels with necessary characteristics
Y(J)S PWE-VPLS Slide 75
Autodiscovery
we have assumed that each PE knows
which PEs participate in particular VPN instance
manual configuration is problematic logistically
autodiscovery refers to automatically finding all PEs in a given VPN
each PE "discovers" other PEs by means of some protocol


BGP
RADIUS (Remote Authentication Dial In User Service)
CE = RADIUS users, PEs = Network Access Servers (NAS)
PE can authenticate CEs and find other PEs

targeted LDP (“Stokes draft”, “Stein-Delord draft” - expired)
advertise FEC in LDP
new TLV in label mapping message contains VPN-id, P or PE, capabilities
Y(J)S PWE-VPLS Slide 76
VPWS Provisioning
Double Sided Provisioning
each AC provisioned with local name, remote PE address, and remote name
during signaling, local name is sent as SAII, remote name as TAII (AGI = null)
to connect 2 ACs by a PW:
local name = remote name(PWid FEC) or
local name of each must be remote name of the other
Single Sided Provisioning with Discovery
each AC provisioned with local name (VPN-id) and AII
during signaling, local name is sent as AGI
to connect 2 ACs by a PW:
both must have the same VPN-id
only one needs to be provisioned with remote name (local name of other AC)
neither needs to be provisioned with the address of the remote PE
during auto-discovery procedure:
each PE advertises its <VPN-id, local AII> pairs
each PE compares its local <VPN-id, remote AII> pairs
with <VPN-id, local AII> pairs from other PEs
if match then need to connect
local name sent as SAII, remote AII sent as TAII, VPN-id as AGI
Y(J)S PWE-VPLS Slide 77
VPLS Provisioning
every VPLS instance is assigned a unique VPN-id
PEs are preconfigured or find each other using auto-discovery
if PE detects VPN-id to which it belongs
it sets up a PW
during signaling
– VPN-id is send as the AGI field
– SAII and TAII are set to null
Y(J)S PWE-VPLS Slide 78
LDP VPLS
ex-“Lasserre-VKompella draft”, now draft-ietf-l2vpn-vpls-ldp
authors: Marc Lasserre - Riverstone and Vach Kompella – Alcatel
supported by Cisco, Nortel, Alcatel, Riverstone, Extreme, Luminous, Corrigent, Hatteras, Overture, RAD
use LDP for
– PW setup and tear-down signaling
– explicit withdrawal of MACs (force relearning)
full mesh of targeted LDP sessions between VPLS-enabled PEs
automatically establish a full mesh of Ethernet PWs
 participating PE sends an unsolicited label mapping message
to every other PE, specifying VPN-ID (preferably with generalized PWid FEC element)

if receiving PE accepts,
it sends a label mapping message back
Y(J)S PWE-VPLS Slide 79
BGP VPLS
ex-“Kompella draft”,
now draft-ietf-l2vpn-vpls-bgp
authors: Kireeti Kompella, Yakov Rekhter – Juniper
uses BGP4 (with multiprotocol extensions) for:



autodiscovery (uses Route Target extended community as VPN-ID)
PW setup and tear-down (uses Network Layer Reachability Information)
force MAC relearning (uses Relearn Sequence Number TLV)
protocol essentially identical to RFC2547bis (to be discussed later)
Y(J)S PWE-VPLS Slide 80
BGP VPLS signaling
define demultiplexor = VPN-ID + ingress PE
VPLS Edge (VE) advertises VPLS NLRIs for each VPLS instance
NLRI defines demultiplexors for all PEs in VPLS instance
extended attribute encodes PE capabilities
if new PE joins VPLS
new NLRI seamlessly adds new label
coalesce to a single NLRI with temporary service disruption
PE sets up PW when it receives an NLRI for VPLS
to leave VPLS instance PE withdraws NLRI
remote PEs remove PWs
Y(J)S PWE-VPLS Slide 81
Generalizations
Y(J)S PWE-VPLS Slide 82
Distributed (Generic) VPLS
CE
U-PE
PE
access
N-PE network
VPLS
CE
CE
U-PE
PE
CE
L2VPN framework allows decomposition of PE

User-Facing PE (U-PE) performs Bridge functions

MAC learning, forwarding decisions
Network-Facing PE (N-PE) performs VPLS functions
establishes tunnels, PWs
V B
U-PE is inexpensive CLE, good for MTU applications
Y(J)S PWE-VPLS Slide 83
Hierarchical VPLS
PE
VPLS
MTU
PE
MTU
VPLS
HVPLS
PE
MTU
VPLS
straight VPLS has a problem – N2 PWs are used
which means N2 LDP sessions, and N2 floods and replications
to improve scalability, can use hub-and-spoke topology
if VPLS is in multi-tenant buildings, local PE is MTU
HVPLS PEs are full mesh, but do not perform bridging
spoke PW set up between PE and MTU (note end-point is virtual bridge)
Y(J)S PWE-VPLS Slide 84
L3VPNs
Y(J)S PWE-VPLS Slide 85
BGP MPLS VPNs (2547bis)
presently most popular provider managed VPN
originally specified in RFC 2547, update in draft called RFC 4364
transports IPv4 (IPv6) traffic in MPLS tunnels
uses BGP for route distribution
since SPs commonly use BGP for routing
2547 is not an overlay model
– CE routers at different sites are not routing peers
– they do not directly exchange routing information
– they don’t even need to know of each other
– so customer needn’t manage a backbone or virtual backbone
– no inter-site routing problems
Y(J)S PWE-VPLS Slide 86
BGP MPLS VPNs (cont.)
only PE routers maintain VPN information
P routers needn’t maintain any customer routing information
C routes either manually configured in PE
or advertised to PE using BGP, OSPF, etc.
PE advertises routes to remote PEs using BGP
remote PEs advertise routes to their CEs using BGP, OSPF, etc.
IP address overlap solved using Route Distinguisher (RD)
Y(J)S PWE-VPLS Slide 87
RFC 4364 (2547bis) architecture
CE not peer to CE
CE peer to PE
C
C
C
CE
C
PE
P
P
PE
C
CE
C
CE is IP router
SP label
ext label
IP Packet
Virtual router (peering) model, not tunneling
PE maintains Virtual Route Forwarding table for each VPN
BGP (with multiprotocol extensions) used for label distribution
in order to support private IP addresses
PE prepends 8B Route Distinguisher (unique to site) to IP address
Y(J)S PWE-VPLS Slide 88
L2VPN
vs.
L3VPN

C switch connects to L2 circuits

C router peers with SP router

BGP or LDP

BGP

all L3 traffic types

limited to IP traffic

only Ethernet L2

supports different L2 technologies

Cs responsible for routing

SP responsible for routing
 “overlay model”

“peer model”

simple customer-SP interface

complex customer-SP interface

C peering scales as VPN size

C peering independent of VPN size
 scaling problem

scales well
Y(J)S PWE-VPLS Slide 89