Transcript Jeremy Brayley Presentation

Leading Edge Routing
MPLS Enhancements to
Support Layer 2 Transport
Services
Jeremy Brayley
[email protected]
Agenda
• Introduction
– Why Layer 2 service over MPLS?
• Provisioning
• Signaling
• Layer 2 encapsulations
• Summary and future work
Copyright © 2001, Laurel Networks, Inc.
What is MPLS?
Multiprotocol Label Switching
• Label switching mechanism with IP
control plane initially designed to
increase forwarding performance
• Label stacking allows tunnel hierarchy for
superior scalability
• New signaling protocols (LDP, RSVP-TE,
CR-LDP, and even mBGP)
• First application - IP Traffic Engineering
• Subsequently several new applications
have been proposed
Copyright © 2001, Laurel Networks, Inc.
New applications for MPLS
• MPLS has been viewed as an IP
traffic engineering technology
– Allows a carrier to increase
operational efficiency, but service
remains the same
• Layer 2 transport is a new
application of MPLS
– MPLS becomes forwarding
infrastructure for a number of services
• IP services
• Private Data (Frame Relay, ATM, Ethernet)
Copyright © 2001, Laurel Networks, Inc.
What problems are we solving?
• Network consolidation
– For carriers offering Private Data and IP
services
• Additional service revenue opportunities
– For carriers currently only offering IP services
• Scalability
– Core switches MPLS tunnels and manages far
fewer connections
• Ease of provisioning
– Touch only edge devices
Copyright © 2001, Laurel Networks, Inc.
Methods of providing layer 2
services over MPLS
• MPLS-based Layer 2VPNs (L2VPN)
– draft-kompella-mpls-12vpn-02.txt
• L2VPN method eases provisioning of full mesh
VPNs
• Policies can be formed to provision hub and
spoke topologies
• Transport of Layer 2 frames over MPLS
– draft-martini-l2circuit-trans-mpls-05.txt
• Defines point-to-point transport using LDP
– draft-martini-l2circuit-encap-mpls-01.txt
• Defines encapsulations for multiple layer 2
services
– Full or partial mesh provisioning requires
automated management tools
Copyright © 2001, Laurel Networks, Inc.
Scalability through label
stacking
P
Layer 2 VCs
2.2.2.2
Tunnel to 2.2.2.2
1.1.1.1
PE
P
IP/MPLS network
PE
VC label
VC label
VC label
Tunnel label determines path to remote edge
VC label designates connection at tunnel endpoint
Copyright © 2001, Laurel Networks, Inc.
Martini method for L2 transport
• All services look like a Virtual Circuit to
MPLS network
• Provision service by associating each
endpoint with a common VC
Identifier(VCID)
• Network automatically determines VC
label and Tunnel label to push on L2
frame
Port/DLCI
Port/DLCI
VCID
Tunnel
label
VC
label
Layer 2 frame
Copyright © 2001, Laurel Networks, Inc.
Provisioning a Layer 2 transport
service
Port 1A, VLAN 100 ->
peer 2.2.2.2, VCID 50
Port 1B, VLAN 200 ->
peer 1.1.1.1, VCID 50
P
1A, 100
1B, 200
601
600
indirect LDP session
to advertise VC labels
PE
1.1.1.1
PE
2.2.2.2
P
LDP advertises label 501 for VCID 50
LDP advertises VC label 500 for VCID 50
PE chooses tunnel to 2.2.2.2, label 600
600
501
Ethernet
PE chooses tunnel to 1.1.1.1, label 601
601
500
Ethernet
Copyright © 2001, Laurel Networks, Inc.
LDP in review
• VC label established via indirect LDP
session
• New Virtual Circuit FEC element defined
– Used in Label Mapping and Label Withdraw
messages
• PE binds VC label to VC Identifier(VCID)
and advertises to remote peer
• LDP message includes:
– Local port identifier
– VC type (FR, ATM, VLAN, etc)
– Local MTU
Copyright © 2001, Laurel Networks, Inc.
Tunnel creation and selection
• Tunnels must exist between PE endpoints
before transport connection may be
established
• Same tunnel may be used for IP and L2
transport traffic
– Eases provisioning
– Scalable
• Service determined by tunnel creation
– RSVP-TE tunnels allow traffic engineering and
resource reservation
– LDP tunnels are plug & play
Copyright © 2001, Laurel Networks, Inc.
Withdrawing labels to indicate
connection status
P
DCLI 100
VCID is down
LMI indicates
status=down
DCLI 200
X
PE
PE
1.1.1.1
2.2.2.2
P
Incoming frames on DLCI
200 are dropped until a
new VC label is received
PE withdraws VC label for connection ID 50
Copyright © 2001, Laurel Networks, Inc.
Layer 2 encapsulation
• Martini drafts define the following
encapsulations over MPLS
–
–
–
–
–
Frame Relay
Ethernet port / 802.1q VLAN
ATM AAL5
ATM cell
PPP/HDLC
Copyright © 2001, Laurel Networks, Inc.
Frame Relay encapsulation
• Ingress device strips the Frame Relay header and
FCS and appends label stack and control word
• Control word carries FECN, BECN, DE, C/R bits
plus PDU length
• Sequence number is optional. It is used to
guarantee in-order delivery of frames
Q.922
address
payload
FCS
Frame Relay frame
4 octets
Tunnel
label
bits
4
4 octets
4 octets
VC
Control
Frame Relay PDU
label
word
Frame Relay over MPLS
1 1 1 1
8
Rsvd B F D C Length
16
Sequence Number
Control Word
Copyright © 2001, Laurel Networks, Inc.
Ethernet encapsulation
• Ingress device strips the Ethernet preamble and
CRC, but transports the entire header
• Control word is not used
• 802.1q VLAN ID may be overwritten at egress
DA
SA
T
payload
FCS
Ethernet frame
4 octets
Tunnel
label
4 octets
VC
Ethernet
header
label
Ethernet over MPLS
Ethernet
payload
Copyright © 2001, Laurel Networks, Inc.
ATM AAL5 encapsulation
• Ingress reassembles AAL5 frames and
strips 8 octet AAL5 trailer
• Required control word includes:
–
–
–
–
Transport type (AAL5 CPCS-PDU or ATM cell)
EFCI, CLP, and C/R bits (CPCS-UU’s LSB)
(CPCS-PDU + control word) length
Sequence number
4 octets
4 octets
Tunnel
label
bits
4 octets
VC
Control
label
word
AAL5 over MPLS
4
11 1 1
8
Rsvd T E L C Length
AAL5 CPCS-PDU
16
Sequence Number
Control Word
Copyright © 2001, Laurel Networks, Inc.
ATM cell mode
• Ingress performs no reassembly
• Control word is optional:
– Length may be used to infer number of cells
– Flags set to zero
4 octets
4 octets
Tunnel
label
VC
label
4 octets
Control
word
52 octets
52 octets
ATM cell #1 ATM cell #2
minus HCS minus HCS
…
ATM cells over MPLS
bits
4
4
8
16
Rsvd
Flags
Length
Sequence Number
Control Word
Copyright © 2001, Laurel Networks, Inc.
Control word in review
• Layer 2 header fields may be discarded at
ingress
• Control word carries variable “flag” bits
– (FR FECN, BECN, C/R, DE, ATM CLP, EFCI, etc)
• Length required when padding small
frames on links which have a minimum
frame size
• Sequence number is optional. It is used
to detect out of order delivery of frames.
bits
4
4
8
16
Rsvd
Flags
Length
Sequence Number
Control Word
Copyright © 2001, Laurel Networks, Inc.
Class of Service considerations
• Ingress device may set MPLS EXP bits to
denote class of service on MPLS network
P
• Should set EXP on both Tunnel and VC
labels
– Tunnel label stripped before egress if PHP is
used
– Allows user to keep 802.1p classification
across MPLS network
Treat according to
Tunnel label EXP
Set Tunnel and
VC label EXP to 010
PE
P
P
Treat according to
VC label EXP
P
PE
Copyright © 2001, Laurel Networks, Inc.
Future work
• Interworking between different frame
types
– Frame Relay / ATM service interworking
(FRF.8.1)
– FR/ATM/Ethernet interworking for IP
• OA&M improvements & SLA measurement
– In-band performance monitoring and
continuity check
Copyright © 2001, Laurel Networks, Inc.
Summary
• L2 transport is a new application of MPLS
– Not just for traffic engineering anymore
• Allows a service provider to expand
IP/MPLS network while offering Layer 2
services
• MPLS label stacking mechanism allows
for core network scalability
– Far fewer connections to manage in core
– Services provisioned at edge
Copyright © 2001, Laurel Networks, Inc.