MPLS Basis

MPLS BasisMPLS Basis
HUAWEI TECHNOLOGIES CO., LTD.
Preface
This course is developed on the basis of multi-protocol label switching technology (MPLS).
The purpose of this course is to introduce basic knowledge on the MPLS technology and describe actual application of MPLS in MSTP transport network.
Guidelines
The key point of this course lies in MPLS technical details and working principle.
The difficulty of this course lies in the understanding of actual application of MPLS in MSTP transport network.
Know the concept and development of MPLS.
Understand MPLS technical details and working principle
Understand actual application of MPLS in transport network.
Actual application of MPLS
MPLS——Multi-Protocol Label Switching
Multi-Protocol: supports multiple L3 protocols, such as IP, IPv6 and IPX. These protocols are located between L2 and L3, so they are also called L2.5 protocols.
Label: is a short, equal-length, processable information content with partial meaning only, topology information excluded.
Switching: MPLS packet switching and forwarding are based on labels. For an IP service, when IP packets enter in the MPLS network, the router in the entrance analyzes the contents of the IP packet and chooses proper labels for these IP packets. All nodes in the MPLS network then depend on these simple labels for forwarding. When the IP packets leave the MPLS network, these labels are separated by the edge router on the exit.
Before MPLS is formally developed, the routing algorithm of a common IP router complies with the longest match principle and is implemented by using software. Limited by the speed of the processor at that time, the routing efficiency is low and cannot meet the network development demand. To increase the forwarding speed of the IP router, many companies successively put forward switching routing schemes based on labels, depending on the advantages of ATM.
Ipsilon put forward IP switching protocol initially. This protocol uses the ATM switch as a router, so the router features high performance of the ATM switch and the performance limit of the traditional router disappears. This brings a great revolution on the router technology and other companies follow the improvement in succession.
CISCO developed Tag Switching.
IBM developed a label switching scheme: Aggregate Route-Based IP Switch (ARIS).
In 1997, multiple companies jointly submit two drafts on the multi-protocol label switching frame and system (MPLS) to IETF. MPLS is based on Tag switching of Cisco and integrates all advantages of other technologies.
Currently, the speed of a router processor is no longer the bottleneck of processing, so MPLS has lost its previous meaning. MPLS is now regarded as a backbone routing and VPN solution.
The common IP router forwards data according to the longest match principle, but the forward speed can hardly reach the line speed, limited by the original processor speed. If short labels are represented as the IP address, the intermediate router can forward data quickly.
The longest match principle is to match the destination IP address and the address of the longest network route in the route table. Suppose there are two routes in the route table: 10.1.2.0/24 and 10.1.3.0/24. If the destination IP address is 10.1.3.4, the 24-bit mask can be used to ensure accurate matching.
The label creation of IP Switching is driven by data stream. Ipsilon defines a set of protocols, including label binding protocol (Ipsilon Flow Management Protocol or IFMP, RFC) and switch management protocol (General Switch Management Protocol or GSMP, RFC). GSMP is used to control a single ATM switch and virtual concatenation spanning the switch.
CISCO Tag Switching: The network consists of Tag Edge Routers and Tag Switching Routers. The IP packets are labeled and encapsulated on Tag Edge Routers. The next hop route confirmation depends on the standard routing algorithm, such as OSPF and BGP. The label binding and distribution adopt the Tag Distribution Protocol (TDP).
Aggregate Route-based IP Switch (ARIS) is a label switching scheme of IBM. Similar to Tag Switching, ARIS also associates labels with the aggregation router. ARIS is different from IP Switching which associates labels with stream. Label binding and the setup of label switching path depend on the control stream (such as route update). The exit router is usually the initiator. ARIS is designed on the basis of using ATM as the data link layer. ARIS is a point-to-point protocol and runs on the IP address of its adjacent router. ARIS also provides the methods of creating and changing labels between adjacent routers. The key to ARIS is Egress Identifier. Label distribution initiates from the exit router and is regularly transmitted to the entrance router through the network.
Internet Engineering Task Force (IETF)
Connectionless-oriented control plane
Connectionless-oriented forward plane
Traditional IP Forwarding
The IP header is analyzed at every hop, so the efficiency is low.
QoS is hard to be deployed and the efficiency is low.
All routers need to know all routes of the entire network.
Analyze the IP header
and map the header
to the next hop
and map the header
to the next hop
and map the header
to the next hop
Before MPLS is formally developed, the routing algorithm of a common IP router complies with the longest match principle and is implemented by using software. Limited by the speed of the processor at that time, the routing efficiency is low and cannot meet the network development demand. To increase the forwarding speed of the IP router, many companies successively put forward switching routing schemes based on labels, depending on the advantages of ATM.
Ipsilon put forward IP switching protocol initially. This protocol uses the ATM switch as a router, so the router features high performance of the ATM switch and the performance limit of the traditional router disappears. This brings a great revolution on the router technology and other companies follow the improvement in succession.
CISCO developed Tag Switching.
IBM developed a label switching scheme: Aggregate Route-Based IP Switch (ARIS).
In 1997, multiple companies jointly submit two drafts on the multi-protocol label switching frame and system (MPLS) to IETF. MPLS is based on Tag switching of Cisco and integrates all advantages of other technologies.
Currently, the speed of a router processor is no longer the bottleneck of processing, so MPLS has lost its previous meaning. MPLS is now regarded as a backbone routing and VPN solution.
Connection-oriented with N2 problems
Routing depends on the link layer and is based on VPI/VCI or labels.
The QoS and real-time services can be ensured.
Virtual channel connection (VCC)
Virtual path connection (VPC)
Layer 3 routing: expandability and flexibility
Layer 2 switching: high reliability and traffic engineering management
+
Core LSR
Advantages of MPLS
The short and fixed-length label replaces the IP header as the forwarding basis to improve the forwarding speed.
IP and ATM are better combined.
Value-added services are provided without affecting the efficiency.
VPN
Why use MPLS
MPLS combines flexible connection and expandability of the network layer with reliable transmission and QoS of ATM label forwarding.
MPLS supports multiple standard routing protocols, such as BGP and OSPF.
MPLS supports multiple label generation protocols, such as LDP and RSVP.
MPLS supports multiple network layer protocols, such as IPv4, IPv6 and IPX.
MPLS solves the problem of QoS.
MPLS features high performance of label forwarding.
MPLS supports L2 and L3 MPLS VPN.
LSP is the tunnel of the public network, so MPLS has natural dominance of implementing VPN. MPLS avoids N2 problems of traditional VPN in configuration and management.
The control on VPN is implemented on PE, thus facilitating management and expansion.
Each VPN forms an independent address; that is, VPNs can reuse their addresses.
Control service isolation and interconnection between services of VPN.
Support traffic engineering.
The MPLS packet header consists of 32 bits (four bytes):
20 bits are used as labels.
Three bits are Experimental, often used as class of service (CoS), but unspecified in the protocol.
One bit is S, used to nest labels and identify whether it is stack bottom or not. In this case, the label can be expanded infinitely.
Eight bits are TTL.
The MPLS packet header is located in front of the IP header (L3) and behind L2 header. Different encapsulation types determine the location of the MPLS header. The labels (VPI/VCI) of other ATM/FR are a part of the MPLS protocol stack.
L2 Header
MPLS Header
IP Header
32 bits
Huawei Confidential
Label Stack
In theory, the label stack can be nested infinitely and thus infinite service support capability can be provided. This is the best feature of MPLS.
L2 Header
MPLS Header
MPLS Header
IP Header
Position of MPLS in the Protocol Stack
MPLS is often located between L2 link layer and L3 IP header.
After an IP packet is added with the MPLS header, L2 packet header encapsulation is still needed.
ATM and FR adopt VPI/VCI and DLCI of previous packet headers as the labels.
FR: The definition of frame is similar to HDLC; Flag is 0x7e, the length of data is variable; Data-Link Connection Identifier (DLCI)
1.unknown
L3Data
6
6
2
2
4
N
CCC is mainly used in point-to-point connection. A label is added. Huawei Ethernet boards do not support the format.
MartinioE is an encapsulation format when the port is an Ethernet port, mainly used to interconnect with other MPLS equipment.
MartinioP is an encapsulation format when the port is VCTRUNK. oP is the abbreviation of On Pos. Martini removes the added DA and SA in Pos encapsulation and saves 12-byte packet header. Thus the data transmission efficiency is highly improved.
VMAN encapsulation format adds a VLAN label and is mainly used to interconnect with the equipment supporting Stack VLAN (QinQ). The convergence points support more VLAN (4K in a standard frame). VMAN is different from MPLS encapsulation.
Martinio encapsulation is divided into Tunnel and VC labels, similar to VPI and VCI of ATM.
The object of Martini encapsulation format can be Ethernet data, so MPLS is applied at a layer lower than L2 and belongs to L2 VPN.
L2.5 is mainly applied on the router and the encapsulation object is IP data. CCC encapsulation can be easily implemented.
Differentiate MPLS and MSTP encapsulation. In the board processing flow, refer to board deployment guides in different links.
Introduction to Relevant Concepts
FEC: Forwarding Equivalence Class, a set of packets (such as a data packet with the same destination address prefix) with similar or identical characteristics which may be forwarded the same way; that is, they may be bound to the same MPLS label.
LSP: Label Switch Path: an FEC data stream is endowed with specific labels at different nodes. Data forwarding is performed based on the labels. The path of FEC data stream is LSP.
LSR: Label Switching Router. LSR is the core switch of the MPLS network, providing label switching and distribution functions.
LER: Label Switching Edge Router. On the edge of MPLS network, the traffic in the MPLS network is divided into different FEC by LER and relevant labels are requested for FEC. LER provides the traffic classification, label mapping and label removal functions.
LSP is a connection-oriented path with source and sink interfaces.
LSP is configured with labels.
LPS is configured with relevant operations.
LSP determines the data output interface.
LSP
The basic unit of the MPLS network is LSR. A network consisting of LSR is MPLS domain (edge router and core router).
Ingress
Egress
LSR
Ingress: The data enters from the user equipment to MPLS network edge equipment and the data packets need be encapsulated.
Egress: When the data enters from the MPLS network core equipment to the edge equipment, MPLS label need be removed.
Intermediate (Transit): When the data enters from one to the other equipment in the MPLS network core, the label is switched.
LSP defines three operations:
Ingress: The data enters from the user equipment to MPLS network edge equipment and the data packets need be encapsulated.
Egress: When the data enters from the MPLS network core equipment to the edge equipment, MPLS label need be removed.
Intermediate (Transit): When the data enters from one to the other equipment in the MPLS network core, the label is switched.
Port P (Provider):
This port refers to a port accessing the core network of the service provider. The port for Huawei equipment refers to a port accessing data packets encapsulated in MPLS format.
Port PE (Provider Edge):
This port is an edge port of the service provider and connects to the user equipment. The port here accesses common Ethernet frames. If data packets encapsulated in MPLS format are accessed and no processing on MPLS encapsulation is needed, the port can be configured as PE.
PE
Ingress
Intermediate
Egress
PE
P
P
P
P
Setup and Structure of LSP
The setup of LSP is a process that you bind FEC with the label and inform the adjacent LSR on the LSP of the binding. To set up the label mapping relationship between adjacent LSRs, you can:
1. Configure static labels without the informing process.
2. Use the label distribution protocol or other protocols.
The setup of LSP is performed by segments.
Tunnel
VC
VC
Take Martinio encapsulation format as an example.
An LSP consists of a Tunnel and VC.Tunnel is a tunnel
of the LSP and VC point-to-point connection is performed.
Structure of LSP
Forwarding Process of LSP
1. The packets in the network are divided into forwarding equivalence class (FEC) according to the characteristics. The packets featuring the same FEC pass the same path (LSP) in the MPLS domain. LER assigns a short and fixed-length label for the FEC packets and then forwards the label from a relevant port.
2. The input/output label mapping table is created on the LSR along the LSP. For the received label packets, LSR follows the label to find out relevant NHLFE in the table and replaces the old label with a new one. Then LSR forwards the label by packets.
3. At the exit of the MPLS domain, the label is removed and the standard IP packet is recovered.
At the network entrance, MPLS assigns FEC featuring special packets and the router can simply forward these packets, compared with regular network layer forwarding. As a result, the forwarding speed is improved.
NHLFE: Next Hop Label Forwarding Entry. The input/output label mapping table is created on the LSR along the LSP. The element of the table is called next hop label forwarding entry.
Data A
Data A
Data B
On the LER, data packets from different ports (or Port+VLAN) are added with relevant labels in compliance with the label processing principle. At the LSR node, the data with relevant labels is forwarded to relevant ports in compliance with the label forwarding table. Other data information is unneeded to be analyzed. When the data reaches the LER, the label is removed as required and previous data is restored and sent to relevant ports.
In the preceding figure, Data A and Data B are configured according to the static labels. The data is sent to the destination site through LSP.
Creating LSP Using MPLS Signaling
Label Distribution Protocol (LDP) is specially used to distribute labels in the MPLS protocol. LDP uses information in the route forwarding table to confirm how to forward data. The information in the route forwarding table is collected by using the IGP and BGP protocols. However, LDP does not relate to all kinds of route protocols directly, but indirectly uses the route information.
LDP is not the unique label distribution protocol. Expanding the existing BGP and RSVP protocols can also support label distribution of MPLS.
Applications of MPLS also need expansion of some route protocols. MPLS-based VPN application needs the expansion of the BGP protocol and MPLS-based traffic engineering needs the expansion of OSPF or IS-IS protocol.
LDP (Label Distribution Protocol)
IGP (Internet Gateway Protocol)
BGP (Border Gateway Protocol)
RSVP (Resource Reservation Protocol)
OSPF (Open the Shortest Path First (link-state routing protocol used for routing IP (TCP/IP))
IS-IS (Intermedia System-Intermedia System)
Questions
Q1: Describe the structure of the MPLS packet header and know the range of labels (maximum value).
Q2: Describe operations of LSP.
Point-to-point virtual shared dedicated service can encapsulate
labels for service data in Port or Port_VLAN mode, thus
implementing virtual sharing of bandwidths.
In the preceding figure, the VCTRUNK between two sites forms an LSP. Encapsulate relevant labels (Tunnel+VC) for different Port data to share bandwidth and isolate from each other.
Tunnel
VC
VC
Virtual shared LAN service
Virtual shared LAN can create LSP bandwidth sharing through different LP ports and VCTRUNK ports of VB, thus implementing virtual sharing of bandwidths.
In the preceding figure, the VCTRUNK between two sites forms an LSP. Encapsulate relevant labels (Tunnel+VC) for different Port data to share bandwidth and isolate from each other.
Tunnel
VC
VC
Tunnel
VC
VC
Tunnel
VC
VC
LP
MAC
VCTRUNK
MAC
Questions
Q1: Describe the application modes of MPLS in optical network transmission equipment.
Q2: In actual application of MPLS, how to choose the relevant encapsulation mode?

Documents

MPLS Basis