WO2014059814A1

WO2014059814A1 - Message forwarding between geographically dispersed network sites

Info

Publication number: WO2014059814A1
Application number: PCT/CN2013/080987
Authority: WO
Inventors: Haifeng Zhao; Junping YOU; Guoliang Zheng
Original assignee: Hangzhou H3C Technologies Co., Ltd.
Priority date: 2012-10-16
Filing date: 2013-08-07
Publication date: 2014-04-24
Also published as: CN103731349B; CN103731349A

Abstract

The present disclosure describes message forwarding between geographically dispersed sites in a network that includes a first ED at a first site and a second ED at a second site. In one example, at the first ED, the first ED advertises to the second ED VLAN information that associates the first VLAN of the first ED with an identifier. The first ED receives MAC address information that includes a MAC address of a second host device advertised by the second ED. The second host device is on a second VLAN that is associated with the same identifier as the first VLAN. The first ED establishes forwarding information to the MAC address of the second host device. When a message addressed to the MAC address of the second host device is received from a first host device on the first VLAN, the first ED forwards the message to the second ED based on the forwarding information to the MAC address.

Description

Message forwarding between geographically dispersed network sites

Background

[0001] In order to improve reliability and provide redundancy, enterprise networks and data centres span across a number of geographically dispersed network sites. Similar services are deployed at the sites connected via layer 2 connectivity. To facilitate dynamic resource allocation and management, virtual machines are allowed to freely migrate among data centers. The process of virtual machine migration may be transparent to users and in which case their IP addresses remain unchanged. Brief Description of Drawings

[0002] By way of non-limiting examples, the present disclosure will be described with reference to the following drawings, in which:

[0003] Fig. 1 is a schematic diagram of an example network for message forwarding between geographically dispersed network sites; [0004] Fig. 2 is a schematic diagram of an example process for message forwarding from a first edge device (ED) to a second ED;

[0005] Fig. 3 is a schematic diagram of an example implementation of the message forwarding process by the second ED in Fig. 2;

[0006] Fig. 4 is a schematic diagram of an example implementation of the message forwarding process by the first ED in Fig. 2; and

[0007] Fig. 5 is a schematic diagram of an example structure of a device capable of acting as an edge device. Detailed Description

[0008] In a network where Virtual Local Area Networks (VLANs) are deployed over geographically dispersed network sites, devices of the same VLAN exchange MAC address information of host devices within that VLAN with each other so that they are able to communicate. For host devices on different VLANs however, it is necessary to make various modifications so that they are on the same VLAN. For example, in Fig. 1, host device 3 connected to edge device ED2 and host device 5 connected to ED3 both belong the same VLAN111 and can communicate with each other. However, if host device 3 on VLAN111 wishes to communicate with host device 1 on a different

VLAN100, modifications are required to ensure that they are on the same VLAN.

However, such modifications may not be straightforward or in some cases possible, and might affect other sites or host devices in the network.

[0009] The present disclosure describes message forwarding between geographically dispersed sites in a network that includes a first ED at a first site and a second ED at a second site.

[0010] In one example, at the first ED, the first ED advertises to the second ED VLAN information that associates the first VLAN of the first ED with an identifier. The first ED receives MAC address information that includes a MAC address of a second host device advertised by the second ED. The second host device is on a second VLAN that is associated with the same identifier as the first VLAN. The first ED establishes forwarding information to the MAC address of the second host device. When a message addressed to the MAC address of the second host device is received from a first host device on the first VLAN, the first ED forwards the message to the second ED based on the forwarding information to the MAC address.

[0011] In another example, at the second ED, the second ED receives VLAN information advertised by the first ED. The received VLAN information associates the first VLAN with an identifier. The second ED advertises MAC address information that includes a MAC address of a second host device to the first ED. The second host device is on a second VLAN associated with the same identifier as the first VLAN in the received VLAN information. When receiving a message from the first ED that is sent by a first host device on the first VLAN and addressed to the MAC address of the second host device, the second ED forwards the message to the second host device on the second VLAN.

[0012] According to the present disclosure, the first host device on the first VLAN is able to communicate with the second host device on the second VLAN because they are associated with the same identifier. As such, if inter- VLAN communication is required between different VLANs, the same identifier may be assigned to them. From the perspective of the first ED, the first ED is able to learn the MAC address of the second host device on the second VLAN. This allows the first ED to forward a message to the second VLAN. From the perspective of the second ED, the second ED advertises the MAC address of the second host device on the second VLAN to the first ED because the second VLAN is associated with the same identifier as the first VLAN. As such, MAC address synchronization is performed between VLANs if they are associated with the same identifier, which indicates that they wish to communicate.

[0013] Examples will be described with reference to accompanying drawings. [0014] Fig. 1 is a schematic diagram of an example network 100 in which multiple edge devices 110 (e.g. EDI, ED2, and ED3) at geographically dispersed network sites are connected via a core network 120. The network 100 may employ suitable technology, such as Ethernet Virtual Interconnect (EVI) and Overlay Transport

Virtualization (OTV) which operate at edge devices 110 etc. EVI, for example, is used to implement a layer 2 virtual private network (L2VPN) technique based on an Internet Protocol (IP) core network. A VPN instance may be established among different edge devices. [0015] In one example implementation, an overlay network (not shown for simplicity) may be used to facilitate VLAN expansion across geographically dispersed sites. The overlay network generally includes an overlay interface and virtual links to carry Layer 2 traffic between sites. For example, the virtual links may be any communication channels over a Layer 3 core network 120. In one example, a physical communication medium may be virtualized to include multiple communication channels such that traffic of one communication channel is separated from that of a different communication channel (e.g. using a suitable identifier). The virtual link may be a Layer 2 virtual link (e.g. virtual Ethernet link) tunnelled through the Layer 3 network using any suitable protocol (e.g. EVI and Generic Routing Encapsulation (GRE) etc.). Layer 2 traffic between sites is encapsulated with an IP header ("MAC in IP") to reach its destination via the core network 120. Traffic is forwarded in the core network 120 based on the IP header.

[0016] The overlay network may be established between edge devices by way of an automatic neighbour discovery process. A link state protocol may be run on this overlay network to advertise information about accessibility of unicast Media Access Control (MAC) addresses of hosts and routers. Once neighbouring relationship is established between edge devices and information of MAC address information is exchanged, traffic may be forwarded between sites. For example, neighbour discovery may be performed using EVI neighbour discovery protocol (ENDP) etc. and MAC address information advertisement may be performed using any suitable link state protocol (LSP) such as Intermediate System-to-intermediate System (IS-IS) protocol etc.

[0017] In the example in Fig. 1, edge devices 110 (one shown for simplicity) are deployed at each site to facilitate message forwarding between sites. Host devices connected to the edge devices 110 send messages within their VLAN. [0018] Edge device EDI connects host devices 1 and 2 to the core network

120. EDI is on both VLAN100 and VLAN110. Host device 1 with MAC address MAC11 belongs to VLAN100 ("local VLAN ID" at EDI). Host device 2, with MAC address MAC 12 belongs to VLAN110. [0019] Edge device ED2 connects host devices 3 and 4 to the core network 120. ED2 is on VLAN111 and VLAN210. Host device 3 with MAC address MAC21 belongs to VLAN111 ("local VLAN ID" at ED2). Host device 4 with MAC address MAC22 belongs to VLAN210. [0020] Edge device ED3 connects host device 5 to the core network 120.

Host device 5 with MAC address MAC31 belongs to VLAN111.

[0021] In a conventional network, different VLANs do not inform each other of MAC address of host devices on the different VLANs. This means, in the example in Fig. 1, host device 1 belonging to VLANIOO ("first VLAN") would not be able to send a message to host device 3 on VLAN111 ("second VLAN") because the MAC address of host device 3 is not advertised by ED2 to ED 1. In other words, there is no MAC address synchronization between VLANIOO and VLAN111.

[0022] According to the present disclosure, a common identifier (e.g. LAN identifier) is assigned to different VLANs to facilitate inter-VLAN communication between ED neighbours 110. For example, VLANIOO and VLAN111 are both assigned with identifier 111 (see 130 in Fig. 1) so that the respective EDI and ED2 would advertise the MAC address information of host devices on VLANIOO and VLAN111 to each other. When EDI forwards a message within VLANIOO, the message will be forwarded to host device on VLAN111 because it is also associated with 111, and vice versa. [0023] To facilitate inter-VLAN communication, different VLANs are assigned with the same identifier (used interchangeably with "LAN identifier" and "LAN ID").

Similarly, EDI and ED2 may assign identifier 222 to VLAN110 and VLAN210 respectively to allow communication between them although they are different VLANs. If a VLAN is not assigned with a LAN identifier, its VLAN ID may be used as the LAN identifier by default. This guarantees that two neighbour EDs on the same VLAN (e.g. ED2 and ED3 on VLAN 111) can also communicate with each other. [0024] Fig. 2 is a schematic diagram of an example process 200 for traffic forwarding between sites. A first ED (e.g. EDI) in the network 100 is connected to a first host device (e.g. host device 1) on a first VLAN (e.g. VLANIOO) communicates with a second ED (e.g. ED2) that is connected to a second host device (e.g. host device 2) on a second VLAN (e.g. VLANl 11). The first ED performs 212, 214 and 216, while the second ED performs 222, 224, 226, as follows:

[0025] At 212, the first ED (e.g. EDI) advertises its VLAN information to a second ED (e.g. ED2). The VLAN information associates the first VLAN (e.g. VLANIOO) with an identifier (e.g. LAN identifier 111). See 150 in Fig. 1, for example.

[0026] At 222, the second ED (e.g. ED2) receives VLAN information advertised by the first ED (e.g. EDI). The VLAN information associates the first VLAN (e.g. VLANIOO) with an identifier (e.g. LAN identifier 111). See 152 in Fig. 1, for example.

[0027] At 224, the second ED (e.g. ED2) sends MAC address information to the first ED (e.g. EDI) based on the VLAN information advertised by the first ED. The MAC address information includes a MAC address of the second host device on the second VLAN (e.g. MAC21 of host device 3 on VLANl 11). The second VLAN (e.g. VLANl 11) is associated with the identifier in the received VLAN information advertised by the first ED. See also 160 in Fig. 1, for example.

[0028] At 214, the first ED (e.g. EDI) receives MAC address information advertised by the second ED (e.g. ED2) that includes the MAC address of the second host device (e.g. host device 3) on the second VLAN (e.g. VLANl 11) and establishes forwarding information to the MAC address (e.g. MAC21). The second VLAN (e.g. VLANl 11) is associated with the identifier in the VLAN information advertised by the second ED. See 162 in Fig. 1, for example. [0029] At 216, when receiving message from the first host device (e.g. host device 1) on the first VLAN (e.g. VLANIOO) that is addressed to the MAC address of the second host device (e.g. MAC21 of host device 3), the first ED (e.g. EDI) encapsulates and forwards the message to the second ED based on the established forwarding information to the MAC address.

[0030] At 226, the second ED receives the message addressed to the MAC address of the second host device (e.g. MAC21 of host device 3). The message is de-encapsulated and forwarded to the second host device (e.g. host device 3).

[0031] Although ED2 is used above as an example "second ED" (i.e. message recipient), it will be appreciated that the above examples may be applied for inter-VLAN communication between VLANIOO on EDI and VLANl 11 on ED3, since both VLANs are also assigned with the same identifier 111.

[0032] Similar to ED2 at 222 in Fig. 2, ED3 also receives VLAN information from EDI that associates VLANIOO with identifier LAN identifier 111 (see 154 in Fig. 1).

[0033] Since local VLANl 11 on ED3 is associated with the same identifier 111, ED3 advertises MAC address information to EDI (see 164 in Fig. 1). Similar to ED2 at 224 in Fig. 2, ED3 advertises MAC address information that includes the MAC31 of host device 5 on VLANl 11.

[0034] The above allows EDI to learn MAC31 such that host device 1 on VLANIOO can send a message to host device 5 on VLANl 11 although they are from different VLANs.

[0035] Examples of VLAN information, MAC address information and forwarding information will be discussed below.

[0036] VLAN information [0037] As a result of the advertisement of VLAN information (e.g. using link state protocol messages), each ED stores its own VLAN information ("local VLAN information") and VLAN information received from other neighbours ("remote VLAN information"). [0038] In the example network 100 in Fig. 1, the following VLAN information is generated and stored.

[0039] VLAN information at EDI :

Table 1(a): Local VLAN information

VLAN ID LAN identifier

VLAN 100 111

VLAN110 222

Table 1(b): Remote VLAN information

[0040] VLAN information at ED2:

Table 2(a): Local VLAN information

VLAN ID LAN identifier

VLAN111 111

VLAN210 222

Table 2(b): Remote VLAN information

Neighbor ED VLAN ID LAN identifier

EDI VLAN 100 1 1 1

EDI VLAN1 10 222

ED3 VLAN1 1 1 1 1 1 [0041] VLAN information at ED3:

Table 3(a): Local VLAN information

Table 3(b): Remote VLAN information

[0042] It can be seen from Table 3(b) that ED3 does not have any VLAN with LAN identifier 222 assigned to it. As such, ED3 will not learn the VLAN information of VLAN110 of EDI and VLAN210 of ED2. This avoids the need to store unnecessary remote VLAN information, and reduces the size of VLAN information stored at the ED and associated processing burden.

[0043] The local VLAN information may also be referred to as "local VLAN configuration entry", which stores a corresponding relationship between a VLAN ID of a local LAN and its assigned identifier. The remote VLAN information as "remote VLAN topology entry", which includes identification information of an ED (e.g. ID), remote VLAN ID and associated identifier.

[0044] MAC address information

[0045] Example implementation of 222, 224 and 226 in Fig. 2 by the second ED will now be explained with reference to Fig. 3, which is similar to Fig. 2 (first host device is not shown for simplicity).

[0046] At 310 (related to 222), the second ED (e.g. ED2) receives VLAN information 312 from the first ED (e.g. EDI). The VLAN information 312 associates VLAN 100 with identifier 111. [0047] At 320 (related to 224), the second ED (e.g. ED2) determines whether a second VLAN (e.g. VLANl 11) associated with the same identifier (e.g. I l l) exists locally. From the VLAN information 322 of the second ED, VLANl 11 is mapped to the same identifier 111.

[0048] If the second VLAN (e.g. VLANl 11) is found, the second ED (e.g. ED2) advertises MAC information of the second host device, which includes the MAC address of the second host device on the second VLAN (e.g. MAC21 of host device 3 on VLANl 11).

[0049] At 330 (related to 226), the second ED (e.g. ED2) receives from the first ED (e.g. EDI) a message 332 addressed to the MAC address of the second host device on the second VLAN (e.g. MAC21 of host device 3 on VLANl 11). The message is forwarded to the second host device; see 334.

[0050] The example 300 in Fig. 3 may be performed by all edge devices 110 such that MAC address information is advertised to each other as long as they have VLANs sharing the same identifier (e.g. I l l) although the VLANs are not necessarily the same (e.g. VLANIOO vs VLANl 11). For example, there are two identifiers 111 and 222 assigned to various VLANs in Fig. 1.

[0051] In relation to identifier 111 , ED 1 advertises MAC 11 (VLAN 100) to ED2 and ED3 since VLANl 11 and VLANIOO are associated with the same identifier 111. Similarly, ED2 advertises MAC21 (VLANl 11) and ED3 advertises MAC 31 (VLANl 11) to EDI .

[0052] In relation to identifier 222, ED 1 advertises MAC 12 (VLAN 110) to ED2 since VLANl 10 and VLAN210 are associated with the same identifier 222. Similarly, ED2 advertises MAC22 (VLAN210) to EDI (VLANl 10 is associated with the same identifier 222 as VLAN210). [0053] According to the example 300 in Fig. 3, if the second ED does not have a second VLAN that shares the same identifier as the first VLAN (e.g. ED3 does not have a VLAN with identifier '222'), it is therefore not necessary to advertise the associated MAC address information to the first VLAN. This reduces unnecessary MAC address synchronization between EDs, which in turn reduces the protocol-related processing burden at the edge devices.

[0054] Advertisement of the MAC address information may be performed using any suitable LSP such as IS-IS etc. For example, an LSP message may carry the MAC address of the second host device (e.g. MAC21) and its VLAN (e.g. VLAN111). [0055] Forwarding information

[0056] Example implementation of 212, 214 and 216 in Fig. 2 by the first ED will now be explained with reference to Fig. 4 (which is similar to Fig. 2 but the second host device is not shown for simplicity).

[0057] At 410, the first ED (e.g. EDI) advertises its VLAN information 412 that associates local VLAN 100 with identifier 111 to the second ED.

[0058] At 420, the first ED (e.g. EDI) receives from the second ED (e.g. ED2) MAC address information 422 that includes the MAC address of the second host device on a second VLAN (e.g. MAC21 of host device 3 on

VLAN111) having the same identifier. The first ED establishes forwarding information to the MAC address.

[0059] In more detail, the first ED (e.g. EDI) searches for a first VLAN that is associated with the same identifier as the second VLAN (e.g. VLAN100 and VLAN111 are both associated with 111). The VLAN information of the second ED (see 422) is searched to find the identifier of the second VLAN (e.g. 111 of VLAN111). The identifier is then used to search the VLAN information of the first ED (see 412) to find a first VLAN having the same identifier (e.g.

VLAN100). .

[0060] At 426, an example forwarding information to the second host device on the second VLAN (e.g. host device 3 on VLANl 11) is shown. The forwarding information includes the VLAN ID of the first VLAN, MAC address of the second host device and corresponding interface information (e.g. tunnel interface information and IP address of ED2 etc.). The interface information may be an EVI tunnel interface number in an EVI network.

[0061] At 430, the first ED (e.g. EDI) receives a message 432 from the first host device on the first VLAN (e.g. host device 1 on VLAN100). The message

432 is addressed to the MAC address of the second host device (e.g. MAC21 of host device 3). Based on the forwarding information to the MAC address 426, the first ED (e.g. EDI) encapsulates and forwards the message to the second ED; see 434. [0062] The examples in Fig. 2 and Fig. 3 may be performed by all edge devices for all VLANs. In the example in Fig. 1, the following forwarding information (also referred to as "MAC address forwarding entry") may be established and stored at the respective edge devices.

[0063] At EDI, the first and third entries in Table 1(c) allow communication between host device 1 (VLAN 100) with host device 3 (MAC21 , VLAN 111) and host device 5 (MAC31 , VLANl 11) respectively. The second entry allows communication between host device 2 (VLANl 10) with host device 4 (MAC31 , VLAN210). Table 1(c): Forwarding information

[0064] At ED2, the first and third entries in Table 2(c) allow communication between host device 3 (VLAN111) with host device 1 (MAC11, VLAN 100) and host device 5 (MAC31 , VLAN111) respectively. The second entry allows communication between host device 4 (VLAN210) with host device 2 (MAC 12, VLAN 110).

Table 2(c): Forwarding information

[0065] At ED3, the entries in Table 3(c) allow communication between host device 5 (VLAN111) with host device 1 (MAC11, VLAN 100) and host device 3 (MAC21, VLAN111):

Table 3(c): Forwarding information

[0066] The IP addresses may be learned through IS-IS protocol for example. When forwarding a message to a neighbour ED (e.g. EDI to ED2), the message is first encapsulated. For example, using GRE encapsulation, the message is encapsulated with an outer IP header, a link layer header and a checksum. The outer IP header includes a source IP address (e.g. IP address of EDI corresponding to the egress interface) and a destination IP address (e.g. IP address of ED2 stored in the forwarding information).

[0067] When forwarding a message received from the first host device, the first ED (e.g. EDI) searches for its destination MAC address (e.g. MAC21) in Table 1(c) and forwards the message to the second ED (e.g. ED2). The message is encapsulated and forwarded via the core network 120 to the second ED. If the destination MAC address is not found, the message will not be forwarded or broadcasted by the first ED. This reduces unnecessary message forwarding and saves network resources.

[0068] Although not shown in Fig. 1 , it will be appreciated that the destination MAC address may be a local MAC address at the first ED, in which case it is not necessary for encapsulation and the message can be forwarded within the network site of the first ED.

[0069] Destination VLAN

[0070] Since a message is forwarded from a first VLAN (e.g. VLAN 100) to a second VLAN (e.g. VLAN111), negotiation may be performed by the relevant edge devices (e.g. EDI and ED2) as to whether to use the ID of the first VLAN or second VLAN during message forwarding.

[0071] If the first VLAN is used (e.g. VLAN100), it is not necessary for the first ED (e.g. EDI) to modify the destination VLAN of the message. Otherwise, if the second VLAN is used (e.g. VLAN111): [0072] The first ED (e.g. EDI) determines the identifier (e.g. I l l) associated with the first VLAN (e.g. VLAN 100), and the second VLAN associated the identifier (e.g. VLAN111). The mapping between the first VLAN and second VLAN may be based on VLAN information advertised by the second ED that associates the second VLAN with the identifier. [0073] The first ED (e.g. EDI) modifies a destination VLAN in the message from the first VLAN to the second VLAN (e.g. VLAN 100 to VLAN111), encapsulates the message with an IP address of the second ED; and forwards the message to the second ED.

[0074] When the second ED (e.g. ED2) receives the message:

[0075] The second ED (e.g. ED2) de-encapsulates the received message.

[0076] If a destination VLAN of the received message is the first VLAN (e.g. VLAN100), the second ED (e.g. ED2) determines the identifier (e.g. I l l) associated with the first VLAN, maps the first VLAN to the second VLAN (e.g. VLAN 100 to VLAN111) and forwards the message to the MAC address of the second host device on the second VLAN (e.g. MAC21 of host device 3 on VLAN111).

[0077] Otherwise, if the destination VLAN is the second VLAN (i.e. the first ED has already modified the destination VLAN from the first to the second), the second ED (e.g. ED2) forwards the message to the MAC address of the second host device on the second VLAN (e.g. MAC21 of host device 3 on VLAN111).

[0078] The above examples, i.e. modifying the VLAN ID at the sender's end or mapping the VLAN ID to a local VLAN ID at the recipient's end may be determined by pre-configuration or by a dynamic negotiation process between the edge devices.

[0079] In practice, the identifier may be marked on a virtual link (e.g. EVI link) between first ED and second ED, and since a virtual link is identified by a tunnel interface number (e.g. EVI tunnel interface) and an IP address of a remote edge device, the identifier may also be included in the forwarding information. The modified VLAN ID may be recorded in the forwarding information, or any other feasible way in practice.

[0080] Example Network Devices 500

[0081] The above examples can be implemented by hardware, software or firmware or a combination thereof. Referring to Fig. 5, an example network device 500 that includes a processor 510, a memory 520 and a network interface device 540 that communicate with each other via bus 530. The processor 710 is to perform processes described herein with reference to Fig. 1 to Fig. 4.

[0082] In one example, the network device 500 is capable of acting as a first ED (e.g. EDI in Fig. 1), in which case the processor is to:

[0083] Advertise VLAN information of the first ED to the second ED. The VLAN information associates the first VLAN with an identifier.

[0084] Receive Media Access Control (MAC) address information advertised by the second ED that includes a MAC address of a second host device and establish forwarding information to the MAC address. The second host device is on a second VLAN that is associated with the same identifier as the first VLAN.

[0085] When a message addressed to the MAC address of the second host device is received from a first host device on the first VLAN, forward the message to the second ED based on the forwarding information to the MAC address.

[0086] In one example, the network device 500 is capable of acting as a second ED (e.g. ED2 in Fig. 1), in which case the processor is to:

[0087] Receive VLAN information advertised by the first ED. The VLAN information associates the first VLAN with an identifier.

[0088] Advertise MAC address information to the first ED that includes a MAC address of a second host device on a second VLAN. The second VLAN is associated with the same identifier as the first VLAN in the received VLAN information. [0089] When receiving a message from the first ED that is sent by a first host device on the first VLAN and addressed to the MAC address of the second host device, forward the message to the second host device on the second VLAN.

[0090] The memory 520 may store any necessary data 522 for facilitating message forwarding between geographically dispersed network sites. For example, the data 522 includes information relating to the first VLAN and second VLAN associated with the same identifier. VLAN information, MAC address information and forwarding information may be stored in the memory 520; see Tables l(a)-(c), 2(a)-(c) and 3(a)-(c).

[0091] The memory 520 may store machine-readable instructions 524 executable by the processor 510 to cause the processor 510 to perform processes described herein with reference to Fig. 1 to Fig. 4. In one example, when the network device 500 is acting as a first ED (e.g. EDI in Fig. 1), the instructions 524 include:

[0092] Advertising instruction to advertise VLAN information of the first ED to the second ED. The VLAN information associates the first VLAN with an identifier.

[0093] Receiving instruction to receive MAC address information advertised by the second ED that includes a MAC address of a second host device, and processing instruction to establish forwarding information to the MAC address. The second host device is on a second VLAN that is associated with the same identifier as the first VLAN.

[0094] Forwarding instruction to, when a message addressed to the MAC address of the second host device is received from a first host device on the first VLAN, forward the message to the second ED based on the forwarding information for transmission to the second host device on the second VLAN. [0095] In one example, when the network device 500 is acting as a second ED (e.g. ED2 in Fig. 1), the instructions 524 include: [0096] Receiving instruction to receive VLAN information advertised by the first ED. The VLAN information associates the first VLAN with an identifier.

[0097] Advertising instruction to advertise MAC address information to the first ED that includes a MAC address of a second host device on a second VLAN. The second VLAN is associated with the same identifier as the first VLAN in the received VLAN information.

[0098] Forwarding instruction to, when receiving a message from the first ED that is sent by a first host device on the first VLAN and addressed to the MAC address of the second host device, forward the message to the second host device on the second VLAN.

[0099] The instructions 524 may further include appropriate instruction to perform the processes described throughout the present disclosure. The instructions 524 may be combined and divided to perform various processes as appropriate.

[00100] In a further example, the network device 500 may include an advertising unit, a receiving unit, an establishing unit, a searching unit and a sending unit (not shown for simplicity).

[00101] The advertising unit is used for advertising a MAC address of a host device in the local VLAN to EDs of other VLANs which need to communicate the local VLAN.

[00102] The receiving unit is used for receiving a MAC address of its local host device advertised by a neighbor ED and receiving a message sent by a host device connected to the ED.

[00103] The establishing unit is used for establishing a MAC address forwarding entry to the corresponding host device when the receiving unit receives a MAC address of its local host device advertised by an EVI neighbor. [00104] The searching unit is used for, when the receiving unit receives a message sent by a host device connected to the present ED, searching the MAC address forwarding entry established by the establishing unit according to the destination MAC address carried by the message. [00105] The sending unit is used for, if it is determined by the searching unit that the message needs to be forwarded to an EVI neighbor, performing EVI encapsulation for this message and sending it to a corresponding EVI neighbor.

[00106] The methods, processes and units described herein may be implemented by hardware (including hardware logic circuitry), software or firmware or a combination thereof. The term 'processor' is to be interpreted broadly to include a processing unit, ASIC, logic unit, or programmable gate array etc. The processes, methods and functional units may all be performed by the one or more processors 510; reference in this disclosure or the claims to a 'processor' should thus be interpreted to mean 'one or more processors'. [00107] Although one network interface device 540 is shown in Fig. 5, processes performed by the network interface device 540 may be split among multiple network interface devices (not shown for simplicity). As such, reference in this disclosure to a 'network interface device' should be interpreted to mean 'one or more network interface devices". [00108] Further, the processes, methods and functional units described in this disclosure may be implemented in the form of a computer software product. The computer software product is stored in a storage medium and comprises a plurality of instructions for making a processor to implement the methods recited in the examples of the present disclosure.

[00109] The figures are only illustrations of an example, wherein the units or procedure shown in the figures are not necessarily essential for implementing the present disclosure. Those skilled in the art will understand that the units in the device in the example can be arranged in the device in the examples as described, or can be alternatively located in one or more devices different from that in the examples. The units in the examples described can be combined into one module or further divided into a plurality of sub-units. [00110] Although the flowcharts described 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 changed 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. [00111] Throughout the present disclosure, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[00112] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

1. A method for message forwarding between geographically dispersed sites in a network, wherein the network comprises a first edge device (ED) at a first site and a second ED at a second site and the method comprises the first ED:

advertising Virtual Local Area Network (VLAN) information of the first ED to the second ED, wherein the VLAN information associates the first VLAN with an identifier;

receiving Media Access Control (MAC) address information advertised by the second ED that includes a MAC address of a second host device and establishing forwarding information to the MAC address, wherein the second host device is on a second VLAN that is associated with the same identifier as the first VLAN; and

when a message addressed to the MAC address of the second host device is received from a first host device on the first VLAN, forwarding the message to the second ED based on the forwarding information to the MAC address.

2. The method of claim 1, wherein establishing the forwarding information to the MAC address of the second host device further comprises:

determining the identifier associated with the second VLAN based on VLAN information advertised by the second ED that associates the second VLAN with the identifier;

determining the first VLAN associated with the identifier; and

establishing the forwarding information that associates the first VLAN, the MAC address of the second host device and interface information to the second ED.

3. The method of claim 2, further comprising:

storing the VLAN information advertised by the second ED as remote VLAN information that associates the second ED, second VLAN and the identifier.

4. The method of claim 1, wherein forwarding the message received from the first host device on the first VLAN and addressed to the MAC address of the second host device further comprises:

determining the identifier associated with the first VLAN, and the second VLAN associated the identifier based on VLAN information advertised by the second ED that associates the second VLAN with the identifier;

modifying a destination VLAN in the message from the first VLAN to the second VLAN;

encapsulating the message with an IP address of the second ED; and

forwarding the message to the second ED.

5. The method of claim 1, wherein the network is an Ethernet Virtual Interconnect (EVI) network or Overlay Transport Virtualization (OTV) network.

6. A method for message forwarding between geographically dispersed sites in a network, wherein the network comprises a first edge device (ED) at a first site and a second ED at a second site and the method comprises the second ED:

receiving Virtual Local Area Network (VLAN) information advertised by the first ED, wherein the VLAN information associates the first VLAN with an identifier; advertising Media Access Control (MAC) address information to the first ED that includes a MAC address of a second host device on a second VLAN, wherein the second VLAN is associated with the same identifier as the first VLAN in the received VLAN information; and

when receiving a message from the first ED that is sent by a first host device on the first VLAN and addressed to the MAC address of the second host device, forwarding the message to the second host device on the second VLAN.

7. The method of claim 6, wherein advertising the MAC address information to the first ED further comprises:

based on the received VLAN information that associates the first VLAN with the identifier, determining whether the second VLAN associated with the identifier exists locally; and if yes, determining the MAC address of the second host device on the second VLAN and advertising the MAC address information; otherwise, not advertising any MAC address information.

8. The method of claim 6, further comprising storing the VLAN information advertised by the first ED as remote VLAN information that associates the first ED, first VLAN and the identifier.

9. The method of claim 6, wherein the message received from the first ED comprises the first VLAN as its destination VLAN, and receiving the message from the first ED further comprises:

de-encapsulating the received message;

if a destination VLAN of the received message is the first VLAN, determining the identifier associated with the first VLAN, map the first VLAN to the second VLAN and forwarding the message to the MAC address of the second host device on the second VLAN;

otherwise, if the destination VLAN is the second VLAN, forwarding the message to the MAC address of the second host device on the second VLAN.

10. A network device for message forwarding between geographically dispersed sites in a network comprising a first edge device (ED) at a first site and a second ED at a second site, wherein the network device is capable of acting as the first ED and comprises a processor to:

advertise Virtual Local Area Network (VLAN) information of the first ED to the second ED, wherein the VLAN information associates the first VLAN with an identifier; receive MAC address information advertised by the second ED that includes a Media Access Control (MAC) address of a second host device and establish forwarding information to the MAC address, wherein the second host device is on a second VLAN that is associated with the same identifier as the first VLAN; and

when a message addressed to the MAC address of the second host device is received from a first host device on the first VLAN, forward the message to the second ED based on the forwarding information to the MAC address.

11. The network device of claim 10, wherein when acting as the first ED and establishing the forwarding information to the MAC address of the second host device, the processor is further to:

determine the identifier associated with the second VLAN based on VLAN information advertised by the second ED that associates the second VLAN with the identifier;

determine the first VLAN associated with the identifier; and

establish the forwarding information that associates the first VLAN, the MAC address of the second host device and interface information to the second ED.

12. The network device of claim 10, wherein when acting as the first ED and forwarding the message received from the first host device on the first VLAN and addressed to the MAC address of the second host device, the processor is further to: determine the identifier associated with the first VLAN, and the second VLAN associated the identifier based on VLAN information advertised by the second ED that associates the second VLAN with the identifier;

modify a destination VLAN in the message from the first VLAN to the second VLAN;

encapsulate the message with an IP address of the second ED; and

forward the message to the second ED.

13. The network device of claim 10, further being capable of acting as the second ED and the processor is further to:

receive VLAN information advertised by the first ED, wherein the VLAN information associates the first VLAN with an identifier;

advertise MAC address information to the first ED that includes a MAC address of a second host device on a second VLAN, wherein the second VLAN is associated with the same identifier as the first VLAN in the received VLAN information; and

when receiving a message from the first ED that is sent by a first host device on the first VLAN and addressed to the MAC address of the second host device, forward the message to the second host device on the second VLAN.

14. The network device of claim 13, wherein when acting as the second ED and advertising the MAC address information to the first ED, the processor is further to: based on the received VLAN information that associates the first VLAN with the identifier, determine whether the second VLAN associated with the identifier exists locally; and

if yes, determine the MAC address of the second host device on the second VLAN and advertise the MAC address information; otherwise, not advertise any MAC address information.

15. The network device of claim 13, wherein when acting as the second ED, the processor is further to:

de-encapsulate the received message;

if a destination VLAN of the received message is the first VLAN, determine the identifier associated with the first VLAN, map the first VLAN to the second VLAN and forward the message to the MAC address of the second host device on the second VLAN;

otherwise, if the destination VLAN is the second VLAN, forward the message to the MAC address of the second host device on the second VLAN.