Abstract If an IP / MPLS network operator adopts L2VPN technology, it can use the IP / MPLS network to support both IP services and data services, and improve the use and management efficiency of network resources. This technology has therefore attracted the attention of operators. This article outlines the three implementations of L2VPN technology, and introduces the development of domestic and foreign standards.
Keywords IP MPLS L2VPN virtual private network
1 Introduction
The L2VPN technology was launched to fully utilize IP / MPLS network resources to support data services. The IP / MPLS network is used to provide transmission channels for Layer 2 data link packets (such as ATM cells, FR frames, and Ethernet frames) in order to achieve Integration of IP network and data network. There are three different forms of L2VPN services that service providers can provide to users, namely VPWS, VPLS and IPLS.
2. L2VPN business form
2.1 Virtual Private Line Service (VPWS)
VPWS provides point-to-point Layer 2 data link frame transfer services. The basic reference model of its service system is shown in Figure 1. The carrier network edge router (PE) and the carrier network internal router (P) are both routers maintained and managed by the carrier. The user edge equipment (CE) accesses the system through Layer 2 links such as Ethernet, ATM or FR . The functions completed by each functional component in the reference model are:
Figure 1 VPWS basic reference model
(1) CE is an access device on the user side, and is responsible for sending user service flows to PE through a directly connected circuit (AC);
(2) The PE router must support L2VPN protocol procedures, including establishing a pseudo-wire connection from PE to PE on the control plane, and completing the encapsulation / de-encapsulation of the layer 2 data link frame to the IP / MPLS label packet on the data plane And corresponding processing functions, and transmit the marked packet to the peer PE through the pseudo line in the PSN tunnel;
(3) The P router supports transparent transmission of L2VPN service flows, does not support L2VPN procedures, and only serves as a bearer channel. The packet switching (PSN) tunnel established between PEs can pass through multiple P routers;
(4) Directly connected circuit (AC) refers to the ATM virtual circuit, FR virtual circuit or Ethernet VLAN link used by users to access the L2VPN system;
(5) Pseudo wire (PW) refers to the connection established by PE using L2VPN signaling. The PE transmits the Layer 2 data frame from the AC to the peer PE through the PW, and the peer PE recovers or regenerates the Layer 2 chain Road frames are transmitted to the peer AC;
(6) Packet Switching (PSN) tunnel refers to the MPLS LSP (Label Switching Path) or L2TP tunnel on the IP / MPLS network. Multiple PWs can be multiplexed in a PSN tunnel from the PE to the peer PE.
It can be seen that VPWS can make full use of IP / MPLS network resources to support point-to-point data services, but the number of PE-to-PE signaling sessions and the number of PSN tunnels in the backbone network may cause scalability problems. In order to solve this problem, the concept of pseudo-line-to-node (S-PE) is introduced. PE devices establish pseudo-line connections with S-PE respectively. The end-to-end connection from PE to PE becomes one or more S-PE The transfer connection reduces the number of end-to-end mesh connections between PEs through S-PE transfer.
2.2 Virtual Private LAN Service (VPLS)
VPLS is a technology for simulating LAN services within the WAN range. Its reference model is shown in Figure 2. The VPLS technology is mainly used to support Ethernet services, and the VPWS technology has been further expanded. On the basis of establishing a pseudo-line connection between PEs, the functional requirements for PE equipment are increased.
Figure 2 VPLS basic reference model
A mesh connection must be established between multiple PEs that support VPLS (you can also use S-PE to establish a star or other form of connection). After the PE receives the Ethernet frame sent by the CE, it determines according to the MAC address in the frame. The PSN tunnel through which the frame is transmitted to another PE. This forwarding function makes the entire VPLS system formally similar to a LAN switch across a wide area network. The PE provides users with an access interface for this LAN switch , Makes users feel very convenient to use. In order to support this function, in addition to supporting the establishment of pseudo lines and the forwarding functions of Layer 2 link frames, PE devices also need to support functions such as MAC address learning, MAC address aging processing, bridge forwarding, and broadcast suppression. .
2.3 Only IP-like LAN services (IPLS) are supported
IPLS is a subset of the VPLS function. This service only supports the user's IP service. It is considered separately because it may provide this service through different mechanisms, so that it can run on a hardware platform that may not support all the functions of VPLS. Except for the following situations, IPLS is very similar to VPLS:
(1) It assumes that the CE device is a host or router rather than a switch;
(2) It assumes that the service only carries IP packets and supports data packets containing IP information, such as ICMP and ARP, and does not support layer 2 packets that do not contain IP information.
3. L2VPN technical standards
The L2VPN standard comes mainly from the IETF's L2VPN working group, which is responsible for providing solutions in three aspects: VPWS, VPLS, and IPLS. In view of the fact that IPLS is a subset of VPLS functions, relevant research is in the process of progress, so the previous IETF standards mainly focused on VPWS and VPLS.
3.1 VPWS standard
There are initially two solutions for the VPWS standard, namely the MarTIni method solution and the Kompella method solution. MarTIni uses the extended LDP signaling method to establish the pseudo line, and Kompella uses the extended BGP signaling method to establish the pseudo line. In the past, the development of VPWS equipment was mainly based on these two solutions. The signaling standards of the two solutions were from MarTIni signaling ( draft-ietf-pwe3-control-protocol) and Kompella signaling (draft-kompella-ppvpn-12vpn).
3.2 VPLS standard
VPLS technology is considered to be based on VPWS, and expands the function of layer 2 switching on PE equipment. The current implementation standards for VPLS and VPWS are unified into the newly drafted L2VPN working group standard draft, which mainly includes 9 standards , That is, the layer 2 virtual private network (L2VPN) framework (draft-ietf-12vpn-12-framework-05), the service requirements of the layer 2 virtual private network provided by the operator (draft-ietf-12vpn-requirements-03), virtual private LAN service (draft-ietf-12vpn-vpls-bgp-02), virtual private LAN service on MPLS (draft-ietf-12vpn-vpls-ldp-05), L2VPN signaling support model and endpoint identifier (draft- ietf-12vpn-signaling-02), only supports IP LAN services (IPLS) (Draft-i-etf-12vpn-ipls-01), VPLSOAM requirements and framework (draft-ietf-12vpn-oam-req-frmk-01 ), VPLS application (draft-ietf-12vpn-vpls-ldp-applic-00).
4 Conclusion
At present, the IETF standards related to L2VPN technology are all drafts, and no formal RFC document has been formed, and the corresponding research work is also in progress. Domestic industry standards for "Layer 2 Virtual Private Network (VPN) Business Technical Requirements" are also being formulated.
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