MPLS Technology fundamentals
Sherif Toulan, P.Eng.,CCIE#4220
Senior Technical Leader, Cisco Systems Canada
EDCS-1470619
Cisco Confidential
1
Sherif Toulan, Bio
• Professional Engineers Ontario, P. Eng.# 90291410
• M. Eng. Degree in Electrical Engineering from University of Toronto, 1991
• Cisco Certified Internetwork Expert, CCIE# 4220, Routing & Switching
• Project Management Professional,
PMP# 511073
• 2000 – Present
Employed by Cisco Systems Canada as Network Design Engineer, working with key Service
Providers (Bell Canada, at&t, France Telecom to deploy MPLS technologies)
• 1991-2000
Employed by Bell Canada as Network Consulting Engineer designing networks for Service
Providers & Enterprise Customers (Banks, Insurance companies,…etc.)
Cisco Systems
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© 2016 Cisco Systems. All rights reserved.
Agenda
“Topics”
 MPLS Technology Basics
 MPLS Traffic Engineering (TE)
 MPLS Layer-2 Virtual Private Networks (L2-VPN) Service
 MPLS Next Generation Technologies
Session Summary
Cisco Systems
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© 2016 Cisco Systems. All rights reserved.
MPLS Technology Basics
Cisco Confidential
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Agenda
 Evolution of MPLS
 MPLS forwarding basics
 MPLS forwarding example
Summary
Cisco Systems
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© 2016 Cisco Systems. All rights reserved.
Evolution of MPLS
“Technology Evolution and Main Growth Areas”
•
Evolved in 1996 & currently 99% of Service Providers have MPLS enabled in their networks
•
Key application initially were Layer-3 VPNs, followed by Traffic Engineering (TE), and Layer-2 VPNs
Optimize MPLS for
packet transport
Optimize MPLS for video
Complete base MPLS portfolio
Bring MPLS to Market
First
L3VPNs
Deployed
Cisco ships
MPLS
1997 1998
Cisco Systems
Large Scale
L2VPN
Deployments
First L2VPN
Deployments
First MPLS TE
Deployments
1999 2000
2001 2002
Large Scale
L3VPN
Deployments
2003 2004
Large Scale
MPLS TE
Deployments
2005 2006
2007 2008
First MPLS
Transport
Profile
Deployments
2009 2010 2011 2012
2013 2014
© 2016 Cisco Systems. All rights reserved.
What Is Multi Protocol Label Switching (MPLS)?
• It’s all about labels …
• Use the best of both worlds
– Layer-2 (ATM/FR): efficient & fast forwarding
– Layer-3 (IP) routing: flexible and scalable
• MPLS forwarding plane
– Use of labels for forwarding Layer-2/3 data traffic
– Labeled packets are being switched instead
of routed
• Leverage layer-2 forwarding efficiency
Multi:
Multi-Protocol: The ability to carry any
payload.
Have:IPv4, IPv6, Ethernet, ATM, FR.
Protocol:
Could do IPX, AppleTalk, DECnet, etc.
Label:
Uses Labels to tell a node what to do
with a packet; separates forwarding
(hop by hop behavior) from routing
(control plane)
Switching:
Routing: IPv4 or IPv6 lookup.
Then forwarding is based on label
Switching.
ATM = Asynchronous Transfer Mode
FR = Frame Relay
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Basic MPLS Forwarding Operations
“How MPLS Labels are Being Used to Establish label switched Path (LSP)?”
MPLS enabled Domain
1. PE (Provider Edge) router
– Label Edge router (LER)
– Imposes and removes MPLS labels
Label Imposition
(Push)
Label Swap
Label Disposition
(PHP)
P
P
Customer data
2. P (Provider) router
– Label switching router (LSR)
– Switches MPLS-labeled packets
CE
PE
3. CE (Customer Edge) router
– Connects customer network to MPLS
network, no labels to be sent to CE nodes
L2
L1
PE
CE
MPLS Service Provider core
CE
CE
PE
P
P
PE
“FEC = Set of all packets that are going to be forwarded in exactly the same way”
“PHP= Penultimate hop popping”
Cisco Systems
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MPLS Labels
“MPLS Label Definition and Encapsulation”
•
Labels used for making forwarding
decision
MPLS Label Entry (4 bytes)
Label = 20 bits
•
Multiple labels (4 bytes = 32 bits) can be
used for MPLS packet encapsulation
•
Outer label always used for switching
MPLS packets in network
•
Inner labels usually used for services
(e.g. Layer 2/Layer 3 VPN)
EXP S
TTL
EXP = Experimental Bits for QoS : 3 Bits; S = Bottom of Stack; TTL = Time to Live
Layer 2 MAC Header
MPLS Label
4 bytes
Layer 3
Packet
MPLS Label Stack (1 label)
QoS = Quality of service
MAC = Media Access Control
Cisco Systems
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MPLS Label Switched Path (LSP) Setup
“LDP for LSP Signaling”
LDP
•
Label Distribution Protocol (LDP)
signaling:
MPLS Forwarding
path
- Label Switched Path (LSP)
– Leverages existing routing protocols (OSPF, ISIS)
•
Exchange of MPLS labels


Label bindings to IP addresses
Downstream MPLS node advertises what label to
use to send traffic to node
MPLS Forwarding
Calculation
MPLS Packet
Encapsulation
MPLS Signaling
Cisco Systems
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- Based on IP routing database
- Shortest-Path based
- Single or Multiple labels
-By each node independently
-Uses existing routing protocols/information
© 2016 Cisco Systems. All rights reserved.
IP Packet Forwarding Example
“Basic IP Packet Forwarding”
•
•
(No MPLS is enabled in the Service Provider network)
IP routing information exchanged between
nodes
– Via IGP (e.g., OSPF, IS-IS)
Packets being forwarded based on
destination IP address
– Lookup in routing table
IP Forwarding
Table
IP Forwarding
Table
Address
I/F
Address
I/F
128.89
1
128.89
0
171.69
1
171.69
1
…
IP Forwarding
Table
Address I/F
128.89
0
171.69
1
…
…
128.89.25.4
1
0
128.89.25.4 Data
0
128.89.25.4 Data
1
1
128.89.25.4 Data
128.89.25.4 Data
171.69.11.1
OSPF = Open Shortest Path First
IS-IS = Intermediate System to Intermediate System
Cisco Systems
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© 2016 Cisco Systems. All rights reserved.
MPLS Path (LSP) Setup with MPLS enabled
Step 1: IP Routing (IGP) Convergence (MPLS enabled, i.e. LDP signaling is enabled)
•
•
•
Enable IGP Routing (OSPF or ISIS) &
MPLS LDP on all core links, i.e. PE-P &
P-P links
Exchange of IP routes in core via:
– OSPF, IS-IS….,etc.
MPLS Forwarding Table MPLS Forwarding Table MPLS Forwarding Table
In
Address
Label Prefix
Out Out
I’face Label
In
Address
Label Prefix
Out Out
I’face Label
128.89
1
128.89
0
171.69
1
171.69
1
…
…
…
…
In
Address
Label Prefix
128.89
0
…
…
Establish IP reachability
0 128.89
0
1
1
You Can Reach 128.89 and
171.69 Thru Me
Routing Updates (OSPF,
ISIS, …)
Cisco Systems
Out Out
I’face Label
12
You Can Reach 128.89 Thru Me
You Can Reach 171.69 Thru Me
171.69
© 2016 Cisco Systems. All rights reserved.
MPLS Path (LSP) Setup with MPLS enabled
Step 2: Assignment of MPLS Labels (MPLS enabled, i.e. LDP signaling is enabled)
•
•
•
Local label mapping are sent to
connected nodes
Receiving nodes update MPLS
forwarding table
MPLS Forwarding Table MPLS Forwarding Table MPLS Forwarding Table
In Address Out Out
In Address Out Out
In Address ) Out Out
Label Prefix I’faceLabel
128.89
1
20
Label Prefix I’faceLabel Label Prefix I’faceLabel
20 128.89
0
30
30
128.89
0
-
-
171.69
1
21
21
171.69
1
36
…
…
…
…
…
…
…
…
…
…
…
…
LDP label advertisement
0 128.89
0
1
Use Label 20 for 128.89 and
Use Label 21 for 171.69
Label Distribution
Protocol (LDP)
Cisco Systems
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Use Label 30 for 128.89
11
Use Label 36 for 171.69
171.69
© 2016 Cisco Systems. All rights reserved.
MPLS Traffic Forwarding with MPLS enabled
Step 3: Hop-by-hop Traffic Forwarding Using Labels (MPLS enabled, i.e. LDP signaling is enabled)
• Ingress PE node adds label to
packet (push)
– Via MPLS forwarding table
• Downstream node use label
for forwarding decision (swap)
– Outgoing interface
– Out MPLS label
• Egress PE removes label and
forwards original packet (pop)
MPLS Forwarding Table MPLS Forwarding Table MPLS Forwarding Table
In Address Out Out
Label Prefix I’faceLabel
128.89
1
20
In Address Out Out
In Address Out Out
Label Prefix I’faceLabel Label Prefix I’faceLabel
20 128.89
0
30
30
128.89
0
-
-
171.69
1
21
21
171.69
1
36
…
…
…
…
…
…
…
…
…
…
…
0 128.89
0
1
128.89.25.4 Data
1
128.89.25.4 Data
14
30 128.89.25.4 Data
20 128.89.25.4 Data
Forwarding based on
Label
Cisco Systems
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171.69
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MPLS Traffic Forwarding with Label Distribution Protocol
(LDP) “Summary”
1.
MPLS increases the speed & performance in Service Provider Network by
doing forwarding based on labels
2.
The MPLS enabled routers (LSRs, LERs) use Label Distribution Protocol
(LDP) to assign & distributes labels, LDP is the signaling protocol used by
MPLS
3.
The MPLS enabled routers advertise their labels to other MPLS enabled
routers, the labels advertise reachability across MPLS network
4.
MPLS label is 4 bytes (32 bits)! & no labels are advertised to Customers
Cisco Systems
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MPLS Traffic Engineering
Cisco Confidential
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Agenda
• MPLS Traffic Engineering (TE) motivation
• MPLS TE Path Selection - Constraint-Based Shortest Path First (CSPF)
• MPLS TE signaling – LSP Setup – Resource Reservation Protocol (RSVP)
Summary
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© 2016 Cisco Systems. All rights reserved.
Link Utilization problem with IGP (OSPF or ISIS)
PE3
PE1
P2
40Mbps
80Mbps
80Mbps
P1
Cost= 10
40Mbps
PE2
P3
Cost= 10
MPLS core
Cost=10
Cost=10
PE4
P5
P4
Cost=10
IP (Mostly) Uses Destination-Based Least-Cost Routing
Flows from PE1, PE2 Merge at P1 and Become Indistinguishable
Upper path is over-utilized
“Lower Path will be Under-Utilized”
IGP = Interior Gateway Protocol (OSPF or IS-IS)
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What MPLS-TE Technology solves?
• MPLS TE solves link utilization problem, i.e. no oversubscription
• P1 is the HEADEND & sees all the links
• P1 computes paths on properties other than just least cost
Next-Hop
• Tunnel 1, Tunnel 2 are manually configured & path is explicitly
enabled from P1 to P3
PE3
Tunnel 1
• Tunnel 1 will take path P1-P2-P3
PE4
Tunnel 2
• Tunnel 2 will take different path P1-P4-P5-P3
Node
P2
Tunnel 1
40Mb
40Mb
MPLS core
Tunnel 1
P3
P1
Tunnel 2
P4
40Mb
PE4
Tunnel 2
40Mb
Tunnel 2
Cisco Systems
PE3
P5
© 2016 Cisco Systems. All rights reserved.
TE Fundamentals – “Building Blocks”

Constraint-Based Shortest Path First (CSPF) only run by Tunnel Headend
– MPLS-TE uses CSPF to create a shortest path based on a series of constraints:

Resource Availability, i.e. available link bandwidth
Step 2: Compute legitimate path:

User constraints ( tunnel priority, link attributes, metric,….etc.)
CSPF does Path Calculation on headend only –

Tunnels are UNI-DIRECTIONAL!
Tunnel Tailend
node
uses IGP advertisements (step 1 to compute
“constrained” path for the TE tunnel
MPLS core
Tunnel Headend
node
Tunnel Midpoint
Step 1:
Information Distribution: via IGP (OSPF or IS-IS)
extensions used to flood bandwidth & topology information
between routers, this extended IGP database will be used
by CSPF to find legitimate path
Cisco Systems
Step 3:
TE Path Setup- via RSVP signaling to
provide link admission control, failure
notification, …etc. Success of this step will
establish the TE tunnel
© 2016 Cisco Systems. All rights reserved.
Constraint-Based Shortest Path First (CSPF) for path computation
TE
Topology
database
From IGP
extended
database
1. TE nodes build a topology database from IGP data base extensions
2. IGP database extensions advertise bandwidth & other link attributes,
IGP database extensions makes the Traffic Engineering Database (TED)
Find shortest
path to R8
with 8Mbps
R1
Tunnel
Headend
3. CSPF uses Traffic Engineering Database (TED) to find best path for
TE tunnel that meets the user constraints & path requested
MPLS
15
10
3
5
10
4. Tunnel can be signaled via Resource Reservation Protocol (RSVP)
R8
once a legitimate path is found
Tailend
8
10
10
n Link with insufficient bandwidth
n Link with sufficient bandwidth
Cisco Systems
© 2016 Cisco Systems. All rights reserved.
How to map Customer Traffic into a TE tunnel?
Tunnel Head end
TE LSP
Customer
Traffic
• Multiple traffic selection options:
1.
Static routes
2.
Policy Based Routing (specific match criteria)
• Traffic enters tunnel at head end
MPLS core
TE LSP = Traffic Engineering label switched path
Cisco Systems
© 2016 Cisco Systems. All rights reserved.
MPLS Traffic Engineering
“Summary”
1.
Traffic Engineering (TE) tunnels are used to manipulate the traffic across the Service provider core
networks & override default IGP behavior, i.e. forward based on least cost
2.
Traffic Engineering (TE) tunnels provide efficient utilization of links based on available bandwidth &
defined user constraints.
3.
Traffic Engineering (TE) tunnels use CSPF to establish the path & RSVP for signaling the TE
tunnels
4.
CSPF used the Traffic Engineering Database (TED) that is built from IGP database TE extensions
5.
Customer traffic can be mapped to TE tunnels either by static route or Policy based routing to follow
a specific path across the core network & as defined in Service Level Agreements between Service
Provider & Customer.
RSVP = Resource Reservation Protocol
IGP = Interior Gateway protocol
TE = Traffic Engineering
Cisco Systems
© 2016 Cisco Systems. All rights reserved.
MPLS Layer-2 Virtual Private Network
(L2-VPN) Services
Cisco Confidential
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Agenda
• Layer-2 Virtual Private Network (VPN) Technology Options
• Layer-2 Virtual Private Wire Service (VPWS) overview (point to point connection)
Summary
Cisco Systems
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Layer-2 Virtual Private Networks (L2-VPN)
“Technology Options- MPLS core”
 L2-VPN Virtual Private Wire Service (VPWS)
– MPLS is required in the core
– Point-to-point
– Referred to as Pseudo wire (PW)
• Virtual Private LAN Service (VPLS)
– Multipoint relies on flooding
– MPLS is required in the core
MPLS Layer-2 VPNs
 Point-to-Point
Layer-2 VPNs (VPWS)
with MPLS core
Multipoint
Layer-2 VPNs (MPLS core)
xEVPN
VPLS
PBB-EVPN
EVPN
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Virtual Private Wire Service (VPWS) Overview
Cisco Confidential
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Pseudo wire (PW) Reference Model for VPWS
• L2 VPNs are built with Pseudo wire (PW) technology over MPLS networks, PW provides Point2Point Service
• Customers can run their own routing,QoS, security,….etc., & no interaction with Service Provider routing protocols
• An Attachment Circuit (AC) is the physical or virtual circuit attaching a CE to a PE
• Customer Edge (CE) equipment perceives a PW as an unshared link or circuit
• MPLS Signaling used for PW : Label Distribution Protocol (LDP)
Emulated Layer-2 Service
Pseudo wire (PW)
PSN
Tunnel
Native
Service
CE1
AC (Ethernet)
AC (ATM)
CE3
PE1
PW1
PW2
Native
Service
PE2
AC (Ethernet)
CE2
AC (ATM)
CE4
Reference: RFC 3985 Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture
Cisco Systems
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VPWS data forwarding Processing
• LDP assigns unique MPLS label for each L2 VPN customer (VC label)
• Tunnel label is MPLS label to switch data packets within Service Provider MPLS network
Tunnel label
swapping through
MPLS cloud
VC and Tunnel
label imposition
Push tunnel label
Push data traffic label
Data traffic
VC label
disposition
Pop
Swap
Tunnel Label= 34
Tunnel Label =45
VC Label= 28
VC Label= 28
VC Label= 28
Data traffic
Data traffic
Data traffic
PE1
P2
P1
CE-1
MPLS
Data traffic
PE2
CE-2
Data Traffic direction
Cisco Systems
© 2016 Cisco Systems. All rights reserved.
Summary
Cisco Systems
1.
Layer-2 VPN enables transport of any traffic over MPLS network by a Service Provider core network
2.
Layer-2 VPN is simple & Service Provider has no control or visibility in customer data
3.
Label Distribution Protocol (LDP) is used for signaling & discovery between Provider Edge (PE)
nodes
4.
Typical applications of L2 VPN are layer-2 business VPN services & Data Center Interconnect
5.
Customer Layer 2 traffic can be mapped onto a Traffic Engineering (TE) tunnel inside the Service
Provider core network
30
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MPLS Next Generation Technologies
Cisco Confidential
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Agenda
•
Motivation for Next Generation MPLS technologies
•
Application Engineered routing
Summary
Cisco Systems
© 2016 Cisco Systems. All rights reserved.
The Full MPLS integrated Network:
“MPLS VPN services,Traffic Engineering technologies”
Layer 2 Circuits available –
Ethernet, ATM, Frame
Relay, PPP, HDLC
CE
Layer 2 Circuits available
Ethernet, ATM, Frame
Relay, PPP, HDLC
Internet
Gateway
PE
CE
PE
MPLS Backbone
LDP & RSVP both
enabled
CE
Layer 2 Circuits available –
Ethernet, ATM, Frame
Relay, PPP, HDLC
Cisco Systems
Internet
Traffic Engineering
CE
Layer 2 Circuits available
Ethernet, ATM, Frame
Relay, PPP, HDLC
© 2016 Cisco Systems. All rights reserved.
Segment Routing Value Proposition
“Simplify the MPLS transport”
 Segment Routing replaces Label Distribution Protocol (LDP) for MPLS control plane:
•
IGP (IS-IS or OSPF) + LDP  IGP (IS-IS or OSPF) with Segment Routing extension = Better Scale
 Segment Routing replaces Resource Reservation Protocol (RSVP) to build Engineered Label Switched paths (LSP):
•
RSVP Traffic engineering (RSVP-TE)  Segment Routing Traffic engineering (SR-TE) = Ease of deployment & troubleshooting
Internet
MPLS VPN services, TE are
enabled
CE
CE
Internet
Gateway
PE
PE
MPLS VPN services, TE are
enabled
Segment Routing
CE
CE
CE
CE
CE
CE
Cont.
Cisco Systems
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Segment Routing (SR) Motivation
“Simplify the MPLS Transport”
SR IETF drafts at : https://xrdocs.github.io/segment-routing/
What’s Segment Routing?
“A new innovation from Cisco, partner with major SP providers and Vendors”
“The source node chooses a path and encodes it in the packet header as an ordered list of Segments”
• Segment Routing is positioned to replace Label Distribution Protocol (LDP)
& Resource Reservation Protocol (RSVP) in control plane to simplify
the MPLS transport
• Segment Routing re-uses MPLS data plane without any change
• IGP + LDP  IGP (ISIS & OSPF) with SR extension
• Replace one protocol: LDP (No IGP/LDP synch issues)
• RSVP-TE traffic engineering  SR Traffic Engineering (SR TE)
• Replace one protocol: RSVP (also can coexist)
Cont.
Cisco
Systems
10:45
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Segment Routing for Application Engineered Routing
“Centralized SDN Controller”

Centralized Optimization for the Path via an SDN controller:
 Tight Integration of Applications with Segment Routing & SDN Controller
 SDN Controller engineers the Segment Routing path to meet the Service Level Agreement (SLA)
SDN
Controller
Need 2Gbps from
Toronto to
Vancouver with SLA
Collect network
status information
66
Toronto
Winnipeg
Edmonton
Whitecourt
Congested
65
9001
Download the path to meet Application
SLA to node Z {66, 9001, 65}
Vancouver
Thunder Bay
Montreal
Calgary
Kelowna
SDN Controller engineers & downloads the Path that meets
Application SLA via Path Computation Element Protocol (PCEP)
SDN= Software Defined Networking
SLA = Service Level Agreement
Cisco Systems
© 2016 Cisco Systems. All rights reserved.
MPLS session
Key Takeaways
1.
MPLS networks consist of PE routers at ingress/egress and P routers in the core
2.
MPLS forwarding operations is based on MPLS labels, hence it speeds up the performance
3.
MPLS label is 4 bytes
4.
Label Distribution Protocol (LDP) is used for MPLS signaling & assigning MPLS labels to IP addresses (prefixes)
5.
Routing protocols (OSPF or IS-IS ) enabled in the core network has to be working properly for proper MPLS
forwarding operation
6.
Traffic Engineering manipulates that path of traffic to better utilize bandwidth & meet Service Level agreements
between Service Provider & Customer
7.
Resource Reservation Protocol (RSVP) is used for Traffic Engineering signaling & setup
8.
Layer 3 VPN requires routing between Customer sites & Service Provider
9.
Layer 2 VPN does not require routing between Customer sites & Service Provider
10. MPLS & its associated technologies are widely deployed across both Service Provider & Enterprise networks
Cisco Systems
OSPF = Open Shortest Path First
IS-IS = Intermediate System to Intermediate System
37
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Thank you.
Acronyms
Acronym
Description
Acronym
Description
MPLS
Multi Protocol label switching
IS-IS
Intermediate system to intermediate system
TE
Traffic Engineering
LSR
Label switch router
VPN
Virtual Private Network
ATM
Asynchronous transfer mode
LER
Label edge router
FR
Frame relay
CSPF
Constraint-based shortest path first
IP
Internet protocol
PBR
Policy based routing
FEC
Forwarding equivalence class
PW
Pseudo wire
LDP
Label distribution protocol
VPLS
Virtual private LAN service
LSP
Label switched path
VPWS
Virtual private wire service
TOS
Type of service
EVPN
Ethernet Virtual Private Network
RSVP
Resource reservation protocol
PBB-EVPN
OAM
Operation, administration, maintenance
Provider backbone bridging Ethernet Virtual Private
Network
BGP
Border gateway protocol
PSN
Packet Switched network
VLAN
Virtual local area network
TTL
Time to live
HDLC
High-level data link control
QoS
Quality of service
PPP
Point-to-point protocol
IGP
Interior gateway protocol
IGP
Interior gateway protocol
OSPF
Open shortest path first
RIPv2
Routing information protocol version 2
MAC
Media Access Control
EIGRP
Enhanced Interior Gateway Routing Protocol
LAC
Link Admission Control
OAM
Operation, Administration & Maintenance
Cisco Systems
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© 2016 Cisco Systems. All rights reserved.