WO2013004184A1

WO2013004184A1 - L2 virtual private network interworking

Info

Publication number: WO2013004184A1
Application number: PCT/CN2012/078209
Authority: WO
Inventors: Zhonghua Gao; Neng Yan
Original assignee: Hangzhou H3C Technologies Co., Ltd.
Priority date: 2011-07-07
Filing date: 2012-07-05
Publication date: 2013-01-10
Also published as: CN102315999A

Abstract

An L2 virtual private network (L2VPN) interworking method is provided. The method comprises: receiving, by a provider edge (PE), a message from a local customer edge (CE), stripping off a link layer header of the message, performing pseudowire (PW) encapsulation on the message, and sending the encapsulated message onto a PW, wherein the PW encapsulation header includes a protocol type field and the value of the protocol field is identical to the protocol type indicated by the value of the protocol type field in the original link layer header of the message. The method further comprises: receiving, by a PE, a message from a remote CE over a PW, stripping off a PW encapsulation header of the message, encapsulating a destination link layer header in the message, and sending the message to a local CE, wherein the value of the protocol type field in the destination link layer header is identical to the protocol type indicated by the value of the protocol type field in the PW encapsulation header.

Description

L2 Virtual Private Network Interworking

Background

Virtual Private Wire Service (VPWS) technique in Layer 2 Virtual Private Network (L2VPN) refers to a technique that interconnects users' layer 2 (L2) networks in different locations via an operator's network, i.e., a technique that provides point-to-point L2 network interconnection across the operator's network. Brief Description of the Drawings

Fig. 1 is a schematic diagram of L2VPN networking for heterogeneous medium interworking according to an example of the present disclosure;

Fig. 2 is a flow chart of a method for L2VPN interworking according to an example of the present disclosure;

Fig. 3 is a flow chart of a method for L2VPN interworking according to an example of the present disclosure;

Fig. 4 is a schematic diagram of message delivery when CE1 sends an IPv4 message to CE2 in the networking shown in Fig. 1 ;

Fig. 5 is a schematic diagram of message delivery when CE1 sends an

IPv6 message to CE2 in the networking shown in Fig. 1 ;

Fig. 6 is a schematic diagram of message delivery when CE1 sends an MPLS message to CE2 in the networking shown in Fig. 1 ;

Fig. 7 is a structural diagram of a PE according to an example of the present disclosure; and

Fig. 8 is a structural diagram of a PE according to another example of the present disclosure

Detailed Description

In general, all those networks interconnected by L2VPN technique are

L2 networks of the same medium, e.g. , attachment circuits on both ends of L2VPN are both Ethernets, or Asynchronous Transfer Mode (ATM) networks, Frame Relay (FR) networks, and the like. However, in some cases, L2 networks interconnected via L2VPN may have different media. With reference to Fig. 1 for example, Fig. 1 illustrates a L2VPN networking for heterogeneous medium in which an example of the present disclosure can be applied. As shown in Fig. 1 , two L2 media are interconnected at two ends of an L2VPN network, wherein at one end is an FR Data Link Connection Identifier (DLCI) network, and at the other end is an 802. 1Q Ethernet Virtual Local Area Network (VLAN). In such cases, an L2VPN technique for heterogeneous medium interconnection is developed, i.e. the so-called L2VPN Interworking technique.

A common L2VPN Interworking technique is the IP Interworking technique, according to which, no matter what kind of L2 link media exist on the two ends of L2VPN, only IPv4 message is transmitted in L2VPN pseudowire (PW). After an IPv4 message reaches a remote provider edge (PE), the remote link layer can decide what link layer encapsulation should be applied to the IPv4 message.

Considering the L2VPN network in Fig. 1 for example, when the FR DLCI network and the Ethernet are interconnected by L2VPN IP Interworking technique, only the user' s IPv4 message can be transmitted in PW, and when the message reaches a network at the opposite end, the link layer header is restored according to the link layer type of the network at the opposite end. For example, when a customer edge 2 (CE2) needs to send a message to CEl , PE2 will strip off the Ethernet link layer header of the message to expose the IPv4 message and transmit the IPv4 message via PW to PEL Upon receiving the IPv4 message, PE1 will restore a corresponding link layer header according to the standard format of the FR DLCI link layer header, and then send it to CEl .

In IP Interworking, only an IPv4 message can be transmitted in PW. Such transmission cannot be accomplished if a message of another network type is delivered between customer edges (CEl and CE2). This is because that, in general, link layers can carry various types of network layer messages, so there should be a field in their link layer encapsulation to clearly identify the type of the network layer messages that they are carrying, so as to hand it over to the correct network layer protocol stack for processing.

Below are two types of link layer encapsulation formats, Ethernet II and Point to Point Protocol (PPP), and definitions of types of the upper layer protocol frames they carry:

Table 1 Ethernet II Link Layer Encapsulation Format Wherein, the field "Type" in table 1 is partially defined as follows: when its value is 0x0800, it indicates that this is an IPv4 message; when its value is 0x8137, it indicates that this is an IPX message;

when its value is 0x86dd, it indicates that this is an IPv6 message; and when its value is 0x8847, it indicates that this is an Multi-Protocol Label Switching (MPLS) message.

Table 2 PPP Link Layer Frame Format

Wherein, the field "protocol" in table 2 is partially defined as follows: when its value is 0x0021 , it indicates that this is an IPv4 message; when its value is 0x002b, it indicates that this is an IPX message;

When its value is 0x0057, it indicates that this is an IPv6 message; and

When its value is 0x0281 , it indicates that this is an MPLS message. In IP Interworking technique, only IPv4 messages can be transmitted in PW. As such, when a remote PE restores the link layer header, the type of the network layer protocol can be filled in as IPv4. This means that no other network layer protocol stack can be used in the user network, e.g. , using both IPv4 and IPv6 stacks, or running MPLS protocol at the same time is not allowed. Because if different types of network layer messages are transmitted in PW, then when the link layer encapsulation is restored at the remote end, it cannot determine how to fill in the field of network layer protocol type in the link layer header.

Another Interworking technique is the so-called Ethernet Interworking technique, i.e. , the L2 link media at both ends of L2VPN are based on Ethernet. For example, in an L2VPN network using Enthernet Interworking technique, there can be Ethernet VLAN link at one end, and Ethernet Over ATM link at the other end. Interconnection can be achieved by transmitting only Ethernet message in PW.

Because Ethernet link layer itself supports running of multiple protocol stacks at the same time, therefore different from IP Interworking, a user can use multiple types of network layer protocol stacks on the link layer simultaneously. However, according to Ethernet Interworking technique, the user' s network must be based on Ethernet, being unable to perform L2VPN interworking for heterogeneous medium between Ethernet link layer and real ATM_^ FR and PPP link layers.

In the following certain examples of the present disclosure will be described in detail with reference to the drawings.

Fig. 2 is a flow chart of a method for L2VPN interworking according to an example of the present disclosure. In the flow diagram of Fig. 2, a method for configuring PEs when an L2VPN network is built may be illustrated. At 201 , when an L2VPN network is built, each PE is configured in a way that the type of a PW to be established is General Interworking. When the L2VPN is established, PEs at both ends automatically negotiate to establish a PW of General Interworking type through Martini signaling according to the configured PW type of General Interworking, and require that messages forwarded over this PW must carry a control word.

Specifically, the PEs at both ends automatically negotiate to establish a PW of General Interworking type through a Label Distribution Protocol (LDP) of Martini signaling.

The PW of General Interworking type is a newly introduced PW type in this example. The pseudowire type value needs to be assigned by the Internet Assigned Numbers Authority (IANA) in a unified way.

The control word of a PW of General Interworking type is different in format from control words of PWs of other types and its format and fields are defined as follows:

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+ _+_+_+_+_+_

|0 0 0 0 I Reserved (12bits) | Protocol Type (16bits) |

Wherein, the field of protocol Type indicates protocol type of the user message carried by the PW, and can use PPP link layer protocol type identifier, see [RFC 1661] and [RFC3818] for details. Below are some examples of its values:

when its value is 0x0021 , it indicates that this is an IPv4 message; when its value is 0x002b, it indicates that this is an IPX message;

when its value is 0x0057, it indicates that this is an IPv6 message; and when its value is 0x0281 , it indicates that this is an MPLS message.

With reference to Fig. 3, Fig. 3 is a flow chart of a method for L2VPN interworking according to an example of the present disclosure. In the flow diagram of Fig. 3, a method of how to transmit messages between two PEs configured according to the method of Fig. 2 may be illustrated. At block 301 , when a user message reaches a local PE and is ready to enter a PW, the local PE will first strip off a link layer header of the message, and then perform PW encapsulation of General Interworking type on the message, and send the encapsulated message to a remote PE.

After PW encapsulation of General Interworking type, the format of the message is as follows:

+ +

Tunnel Label |

+ +

PW label |

+ +

Control Word | Payload |

Wherein, the format of the control word is the format of control word of a PW of General Interworking type described above with reference to Fig. 2. The value of the Protocol Type field in the control word needs to be matched with the value of the protocol type in the original link layer header of the user message, that is, the protocol type indicated by the value of the protocol type field in the control word needs to be identical to the protocol type indicated by the value of the protocol type field in the original link layer header of the user message. And the payload therein can be a payload of any network layer protocol.

At block 302, when a remote PE receives a message over a PW, it first strips off the PW encapsulation header of the message, encapsulates a destination link layer header in the message, and then sends the message out. Wherein, the value of the protocol type in the destination link layer header needs to be matched with the value of the protocol type in the PW control word of the PW encapsulation header.

With the example of present disclosure given above, a user network can use multiple types of network layer protocol stacks at the same time under any networking with heterogeneous medium L2VPN interworking.

In the following, with reference to Fig. 4-Fig. 6, examples of message delivery when CE1 sends various types of messages to CE2 in the networking shown in Fig. 1 according to an example of the present disclosure will be described. As shown in Fig. 1 , an FR DLCI link layer and Ethernet link layer span a public network and establish an L2VPN network with heterogeneous medium interconnected. Assuming that users at both ends utilize such three types of protocol stacks as IPv4, IPv6 and MPLS at the same time.

Fig. 4 shows a schematic diagram of message delivery when CE1 sends an IPv4 message to CE2. As shown in Fig. 4, the process for message delivery is as follows:

a first message format is the format of the IPv4 message sent by CE1 , wherein the control field of the FR DLCI link layer header and the Network Layer Protocol Identifier (NLPID) field include a protocol type field, the value of which is 03 CC, indicating that it is an IPv4 message; a second message format is the format of the message after it is received by PE1 from CE1 and its FR DLCI link layer header is stripped off and a PW encapsulation is performed thereon, wherein the control word field includes a protocol type field, the value of which is 0021 , indicating that it is an IPv4 message;

a third message format is the format of the message received by PE2 over PW, and this format is the same as the second message format; and the fourth message format is the format of the message after it is received by PE2 over the PW and its PW encapsulation header is stripped off and according to the destination link layer (i.e. Ethernet link layer), an Ethernet link layer header is encapsulated in the message, wherein the field of Ethernet type (i.e. Eth type) includes a protocol type field, the value of which is 0800, indicating that it is an IPv4 message. Wherein, the destination MAC address (DA) is the MAC address of CE2 and the source MAC address (SA) is the MAC address of an interface of PE2.

Fig. 5 shows a schematic diagram of message delivery when CE1 sends an IPv6 message to CE2. As shown in Fig. 5, the process for message delivery is as follows:

a first message format is the format of the IPv6 message sent by CE1 , wherein the control field of the FR DLCI link layer header and the NLPID field include a protocol type field, the value of which is 86dd, indicating that it is an IPv6 message;

a second message format is the format of the message after it is received by PEl from CEl and its FR DLCI link layer header is stripped off and a PW encapsulation is performed thereon, wherein the control word field includes a protocol type field, the value of which is 0057, indicating that it is an IPv6 message;

a third message format is the format of the message received by PE2 over PW, and this format is the same as the second message format; and the fourth message format is the format of the message after it is received by PE2 over the PW and its PW encapsulation header is stripped off and according to the destination link layer (i.e. Ethernet link layer) an Ethernet link layer header is encapsulated in the message, wherein the field of Ethernet type (i.e. Eth type) includes a protocol type field, the value of which is 86dd, indicating that it is an IPv6 message. Wherein, the destination MAC address (DA) is the MAC address of CE2 and the source MAC address (SA) is the MAC address of an interface of PE2.

Fig. 6 shows a schematic diagram of message delivery when CEl sends an MPLS message to CE2. As shown in Fig. 6, the process for message delivery is as follows:

a first message format is the format of the MPLS message sent by CEl , wherein the control field of the FR DLCI link layer header and the NLPID field include a protocol type field, the value of which is 8847, indicating that it is an MPLS message;

a second message format is the format of the message after it is received by PEl from CEl and its FR DLCI link layer header is stripped off and a PW encapsulation is performed thereon, wherein the control word field includes a protocol type field, the value of which is 0281 , indicating that it is an MPLS message;

a third message format is the format of the message received by PE2 over PW, and this format is the same as the second message format; and the fourth message format is the format of the message after it is received by PE2 over the PW and its PW encapsulation header is stripped off and according to the destination link layer (i.e. Ethernet link layer) an Ethernet link layer header is encapsulated in the message, wherein the field of Ethernet type (Eth type) includes a protocol type field, the value of which is 8847, indicating that it is an MPLS message. Wherein, the destination MAC address (DA) is the MAC address of CE2 and the source MAC address (SA) is the MAC address of an interface of PE2.

Please be noted that VPWS provides a type of virtual private wire service, i.e. , a point-to-point virtual private wire that spans the public network, so in normal use, it is point-to-point links that interconnect with each other. However, during an actual application, link layers interconnected by heterogeneous medium may not be a P2P type, i.e., they may be a point-to-multiple-points (P2MP) or broadcast type, such as FR or Ethernet network. In this case, for a message coming out of a PW, because the message does not include any destination address information therein, therefore the PE cannot perform L2 addressing according to its content and the PW cannot perform multicast or broadcast processing for the message. In this case, the following processing can be performed:

For any message received over a PW, the PE only sends it to a fixed CE. For example, on an Ethernet, a static MAC address of a CE is configured on the PE. For any message received over a PW, the PE only sends the message to the configured CE. The processing in this case is actually the same as the processing in IP Interworking.

With reference to Fig. 7 now, Fig. 7 shows a structural diagram of a PE according to an example of the present disclosure. The PE can be located in an L2VPN. As shown in Fig. 7, the PE includes an incoming PW message processing module 72 and an outgoing PW message processing module 73.

The incoming PW message processing module 72 is configured to receive a message from a local CE, strip off a link layer header of the message, perform PW encapsulation on the message and send the encapsulated message onto a PW, wherein a control word of the PW encapsulation header includes a protocol type field and the value of the protocol field is identical to the protocol type indicated by the value of the protocol type field in the original link layer header of the message. And the outgoing PW message processing module 73 is configured to receive over a PW a message from a remote CE, strip off a PW encapsulation header of the message, encapsulate a destination link layer header in the message, and send the message to a local CE, wherein the value of the protocol type field in the destination link layer header is identical to the protocol type indicated by the value of the protocol type field in the PW encapsulation header.

With reference to Fig. 8, Fig. 8 shows a structural diagram of a PE according to another example of the present disclosure. Here, except for block 71 , the PE of Fig. 8 comprises the same blocks (i.e. 72 and 73) as the PE of Fig. 7. Therefore, identical blocks having similar/ same implementations and/or functions are denoted by the same numerals, and won't be described in detail herein for sake of simplicity. Referring to the example of Fig. 8, the PE in Fig. 8 further includes a PW establishing module 71. The PW establishing module 71 is configured to, when the L2VPN is established, negotiate with a remote PE to establish a PW of general interworking type and require that messages forwarded over said PW must carry a control word, wherein the control word is located in the PW encapsulation header and includes a protocol type field.

The above examples can be implemented by hardware, software or firmware or a combination thereof. For example the various methods, processes and functional modules described herein may be implemented by a processor (the term processor is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate array etc.). The processes, methods and functional modules may all be performed by a single processor or split between several processers; reference in this disclosure or the claims to a 'processor' should thus be interpreted to mean 'one or more processors' . The processes, methods and functional modules may be implemented as machine readable instructions executable by one or more processors, hardware logic circuitry of the one or more processors or a combination thereof. Further the teachings herein may be implemented in the form of a software product. The computer software product is stored in a storage medium and comprises a plurality of instructions for making a computer device (which can be a personal computer, a server or a network device such as a router, switch, access point etc.) implement the method recited in the examples of the present disclosure.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the processes or blocks of any method so disclosed, may be combined in any combination, except combinations where at least some of such features and/or processes or blocks are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The figures are only illustrations of an example, wherein the modules or procedure shown in the figures are not necessarily essential for implementing the present disclosure. Moreover, the sequence numbers of the above examples are only for description, and do not indicate an example is more superior to another.

Those skilled in the art can understand that the modules in the device in the example can be arranged in the device in the example as described in the example, or can be alternatively located in one or more devices different from that in the example. The modules in the aforesaid example can be combined into one module or further divided into a plurality of sub-modules.

Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. For example, the order of execution of two or more blocks may be scrambled relative to the order shown. Also, two or more blocks shown in succession may be executed concurrently or with partial concurrence. All such variations are within the scope of the present disclosure.

Claims

1. An L2 virtual private network (L2VPN) interworking method, wherein the method comprises:

receiving, by a provider edge (PE), a message from a local customer edge (CE), stripping off a link layer header of the message, and performing pseudowire (PW) encapsulation on the message, and sending by the PE the encapsulated message onto a PW, wherein the PW encapsulation header includes a protocol type field and the value of the protocol type field is identical to the protocol type indicated by the value of the protocol type field in the original link layer header of the message; and

receiving, by a PE, a message from a remote CE over a PW, stripping off a PW encapsulation header of the message, encapsulating a destination link layer header in the message, and sending the message to a local CE, wherein the value of the protocol type field in the destination link layer header is identical to the protocol type indicated by the value of the protocol type field in the PW encapsulation header.

2. The method according to claim 1 , wherein when the L2VPN is established, said PE and the remote PE negotiate to establish a PW of general interworking type, and require that messages forwarded over said PW must carry a control word, wherein the control word is located in the PW encapsulation header and includes a protocol type field.

3. The method according to claim 1 , wherein said message is an IPv4 or IPv6 or IPX or Multi-Protocol Label Switching (MPLS) message.

4. A provider edge (PE) in an L2 virtual private network (L2VPN), wherein said PE comprises:

an incoming PW message processing module that receives a message from a local customer edge (CE), strips off a link layer header of the message, performs PW encapsulation on the message, and sends the encapsulated message onto a PW, wherein the PW encapsulation header includes a protocol type field and the value of the protocol type field is identical to the protocol type indicated by the value of the protocol type field in the original link layer header of the message; and

an outgoing PW message processing module that receives over a PW a message from a remote CE, strips off a PW encapsulation header of the message, encapsulates a destination link layer header in the message, sends the message to a local CE, wherein the value of the protocol type field in the destination link layer header is identical to the protocol type indicated by the value of the protocol type field in the PW encapsulation header.

5. The PE according to claim 4, wherein said PE further includes:

a PW establishing module that, when the L2VPN is established, negotiates with a remote PE to establish a PW of general interworking type, and requires that the message forwarded over said PW must carry a control word, wherein the control word is located in the PW encapsulation header and includes a protocol type field.

6. The PE according to claim 4, wherein the message received by the incoming PW message processing module is an IPv4 or IPv6 or IPX or

Multi-Protocol Label Switching (MPLS) message; and the message received by the outgoing PW message processing module is an IPv4 or IPv6 or IPX or Multi-Protocol Label Switching (MPLS) message.