5.1.1. VPLS Packet Walk-Through in Network Mode

This section provides an example of VPLS processing of a customer packet sent across the network from site-A, which is connected to PE-Router-A through a 7210 SAS to site-C, which is connected through 7210 SAS to PE-Router-C (Figure 56) in an H-VPLS configuration. This section does not describe the processing on the PE routers, but only on 7210 SAS routers.

Figure 56:  VPLS Service Architecture 

5.1.2. VPLS Packet Walk-Through in Access-uplink Mode

This section provides an example of VPLS processing of a customer packet sent across the network from site-A, which is connected to PE-Router-A through a 7210 SAS to site-C, which is connected through 7210 SAS to PE-Router-C (Figure 56) in an H-VPLS configuration. This section does not describe the processing on the PE routers but only on 7210 SAS routers.

5.2.1. VPLS Enhancements

The Nokia VPLS implementation includes several enhancements beyond basic VPN connectivity. The following VPLS features can be configured individually for each VPLS service instance:

5.2.2. VPLS over MPLS in Network Operating Mode

The VPLS architecture proposed in draft-ietf-ppvpn-vpls-ldp-0x.txt specifies the use of provider equipment (PE) that is capable of learning, bridging, and replication on a per-VPLS basis. The PE routers that participate in the service are connected using MPLS Label Switched Path (LSP) tunnels in a full-mesh composed of mesh SDPs or based on an LSP hierarchy (Hierarchical VPLS (H-VPLS)) composed of mesh SDPs and spoke-SDPs. The 7210 SAS supports only H-VPLS.

Multiple VPLS services can be offered over the same set of LSP tunnels. Signaling specified in RFC 4905 is used to negotiate a set of ingress and egress VC labels on a per-service basis. The VC labels are used by the PE routers for de-multiplexing traffic arriving from different VPLS services over the same set of LSP tunnels.

VPLS/H-VPLS is provided over MPLS by:

5.2.3. VPLS over QinQ Spokes for 7210 SAS Devices Configured in Access-uplink Operating Mode

7210 SAS devices configured in access-uplink operating mode support QinQ spokes or dot1q spokes, which allows them to connect to upstream PE nodes which provides IP/MPLS transport.

VPLS is provided over QinQ/Dot1q spokes by:

5.2.4. VPLS MAC Learning and Packet Forwarding

The 7210 SAS edge devices perform the packet replication required for broadcast and multicast traffic across the bridged domain. MAC address learning is performed by the 7210 SAS device to reduce the amount of unknown destination MAC address flooding.

Each 7210 SAS maintains a Forwarding Information Base (FIB) for each VPLS service instance, and learned MAC addresses are populated in the FIB table of the service. All traffic is switched based on MAC addresses and forwarded between all participating nodes using the LSP tunnels unknown destination packets (for example, the destination MAC address has not been learned) are forwarded on all LSPs to all participating nodes for that service until the target station responds and the MAC address is learned by the 7210 SAS associated with that service.

5.2.5. IGMP Snooping in a VPLS Service

Note: IGMP snooping is supported on all 7210 SAS platforms as described in this document, including those configured in the access-uplink operating mode. This section provides information about IGMP snooping support in a VPLS service. It does not apply to R-VPLS services. IGMP snooping can also be enabled for R-VPLS services. See R-VPLS and IGMPv3 Snooping for more information.

In Layer 2 switches, multicast traffic is treated as an unknown MAC address or broadcast frame, which causes the incoming frame to be flooded out (broadcast) on every port within a VLAN. Although this is acceptable behavior for unknown and broadcast frames, this flooded multicast traffic may result in wasted bandwidth on network segments and end stations because IP multicast hosts can join and be interested in only specific multicast groups.

IGMP snooping uses information in Layer 3 protocol headers of multicast control messages to determine the processing at Layer 2. By doing so, an IGMP snooping switch provides the benefit of conserving bandwidth on those segments of the network in which no node has expressed interest in receiving packets addressed to the group address.

Note: References to SDP in the following section about IGMP snooping are applicable only to 7210 SAS platforms operating in network mode.

IGMP snooping can be enabled in the context of VPLS services. The IGMP snooping optimizes the multicast data flow to only those SAPs or SDPs that are members of the group. The system builds a database of group members for each service by listening to IGMP queries and reports from each SAP or SDP, as follows.

The following is a list of supported IGMP snooping features.

5.2.6. Multicast VLAN Registration (MVR) Support in VPLS Service

Multicast VPLS Registration (MVR) is a bandwidth optimization method for multicast in a broadband services network. MVR allows a subscriber on a port to subscribe and unsubscribe to a multicast stream on one or more network-wide multicast VPLS instances.

MVR assumes that subscribers join and leave multicast streams by sending IGMP join and leave messages. The IGMP leave and join message are sent inside the VPLS to which the subscriber port is assigned. The multicast VPLS is shared in the network while the subscribers remain in separate VPLS services. Using MVR, users on different VPLS cannot exchange information between them but still multicast services are provided.

On the MVR VPLS, IGMP snooping must be enabled. On the user VPLS, IGMP snooping and MVR work independently. If IGMP snooping and MVR are both enabled, MVR reacts only to join and leave messages from multicast groups configured under MVR. Join and leave messages from all other multicast groups are managed by IGMP snooping in the local VPLS. This way, potentially several MVR VPLS instances could be configured, each with its own set of multicast channels.

MVR by proxy — In some situations, the multicast traffic should not be copied from the MVR VPLS to the SAP on which the IGMP message was received (standard MVR behavior) but to another SAP. This is called MVR by proxy, shown in Figure 61.

Figure 61:  MVR and MVR by Proxy 

5.2.7. Layer 2 Forwarding Table Management

The following sections describe VPLS features related to management of the FIB.

5.2.7.8. MAC Move

The MAC move feature is useful to protect against undetected loops in a VPLS topology as well as the presence of duplicate MACs in a VPLS service.

If two clients in the VPLS have the same MAC address, the VPLS will experience a high relearn rate for the MAC. When MAC move is enabled, the 7210 SAS will shut down the SAP or spoke-SDP and create an alarm event when the threshold is exceeded.

MAC move allows sequential order port blocking. By configuration, some VPLS ports can be configured as “non-blockable” which allows simple level of control which ports are being blocked during loop occurrence.

5.2.7.8.1. Split Horizon SAP Groups and Split Horizon Spoke-SDP Groups

Note: Per-service split horizon groups are supported on all 7210 SAS platforms as described in this document, except those operating in access-uplink mode.

Within the context of VPLS services, a loop-free topology inside a fully meshed VPLS core is achieved by applying a split-horizon forwarding concept.The packets received from a mesh SDP are never forwarded to other mesh SDPs within the same service. The advantage of this approach is that no protocol is required to detect loops within the VPLS core network.

In applications such as DSL aggregation, it is useful to extend this split-horizon concept also to groups of SAPs and/or spoke-SDPs. This extension is referred to as a split horizon SAP group. Traffic arriving on a SAP or a spoke-SDP within a split horizon group will not be forwarded to other SAPs and spoke-SDPs configured in the same split horizon group, but will be forwarded to other SAPs/spoke-SDPs, which are not part of the split horizon group.

5.2.7.8.2. Configuration Guidelines for Use of Split Horizon Group in a VPLS Service

1. On 7210 SAS-M, 7210 SAS-T, and 7210 SAS-Sx/S 1/10GE operating in network mode, mesh SDPs cannot be configured in a service which uses split horizon group (SHG). Conversely, if a service has a mesh SDP configured, split horizon group cannot be used in the same service.
2. On 7210 SAS-Mxp, service based SHG can be configured along with mesh SDPs and spoke-SDPs.

5.2.8. VPLS and Spanning Tree Protocol

The Nokia VPLS service provides a bridged or switched Ethernet Layer 2 network. Equipment connected to SAPs forward Ethernet packets into the VPLS service. The 7210 SAS participating in the service learns where the customer MAC addresses reside, on ingress SAPs.

Unknown destinations, broadcasts, and multicasts are flooded to all other SAPs in the service. If SAPs are connected together, either through misconfiguration or for redundancy purposes, loops can form and flooded packets can keep flowing through the network. The Nokia implementation of the Spanning Tree Protocol (STP) is designed to remove these loops from the VPLS topology. This is done by putting one or several SAPs in the discarding state.

The Nokia implementation of the Spanning Tree Protocol (STP) incorporates some modifications to make the operational characteristics of VPLS more effective.

The STP instance parameters allow the balancing between resiliency and speed of convergence extremes. Modifying particular parameters can affect the behavior. For information about command usage, descriptions, and CLI syntax, refer to Configuring a VPLS Service with CLI.

5.2.8.4. Provider MSTP

Note: Provider MSTP is only supported on platforms that support PBB, and therefore is only supported on 7210 SAS-M and 7210 SAS-T operating in the network mode.

Provider MSTP is specified in (IEEE-802.1ad-2005). It uses a provider bridge group address instead of a regular bridge group address used by STP, RSTP, MSTP BPDUs. This allows for implicit separation of source and provider control planes.

The 802.1ad access network sends PBB PE P-MSTP BPDUs using the specified MAC address and also works over QinQ interfaces. P-MSTP mode is used in PBBN for core resiliency and loop avoidance.

Similar to regular MSTP, the STP mode (for example, PMSTP) is only supported in VPLS services where the m-VPLS flag is configured.

5.2.8.4.1. MSTP General Principles

MSTP represents modification of RSTP which allows the grouping of different VLANs into multiple MSTIs. To enable different devices to participate in MSTIs, they must be consistently configured. A collection of interconnected devices that have the same MST configuration (region-name, revision and VLAN-to-instance assignment) comprises an MST region.

There is no limit to the number of regions in the network, but every region can support a maximum of 16 MSTIs. Instance 0 is a special instance for a region, known as the Internal Spanning Tree (IST) instance. All other instances are numbered from 1 to 4094. IST is the only spanning-tree instance that sends and receives BPDUs (typically BPDUs are untagged). All other spanning-tree instance information is included in MSTP records (M-records), which are encapsulated within MSTP BPDUs. This means that single BPDU carries information for multiple MSTI which reduces overhead of the protocol.

Any specific MSTI is local to an MSTP region and completely independent from an MSTI in other MST regions. Two redundantly connected MST regions will use only a single path for all traffic flows (no load balancing between MST regions or between MST and SST region).

Traditional Layer 2 switches running MSTP protocol assign all VLANs to the IST instance per default. The operator may then “re-assign” individual VLANs to a specific MSTI by configuring per VLAN assignment. This means that an SR-series PE can be considered as the part of the same MST region only if the VLAN assignment to IST and MSTIs is identical to the one of Layer 2 switches in access network.

5.2.8.4.2. MSTP in the 7210 SAS Platform

The 7210 SAS platform uses a concept of mVPLS to group different SAPs under a single STP instance. The VLAN range covering SAPs to be managed by a specific mVPLS is declared under a specific mVPLS SAP definition. MSTP mode-of-operation is only supported in an mVPLS.

When running MSTP, by default, all VLANs are mapped to the CIST. On the VPLS level VLANs can be assigned to specific MSTIs. When running RSTP, the operator must explicitly indicate, per SAP, which VLANs are managed by that SAP.

5.2.9. VPLS Redundancy

The VPLS standard (RFC 4762, Virtual Private LAN Services Using LDP Signalling) includes provisions for hierarchical VPLS, using point-to-point spoke-SDPs. Two applications have been identified for spoke-SDPs:

In both applications the spoke-SDPs serve to improve the scalability of VPLS. While node redundancy is implicit in non-hierarchical VPLS services (using a full mesh of SDPs between PEs), node redundancy for spoke-SDPs needs to be provided separately. In VPLS services, only two spoke-SDPs are allowed in an endpoint.

The 7210 SAS routers have implemented special features for improving the resilience of hierarchical VPLS instances, in both MTU and inter-metro applications.

5.2.9.1. Spoke-SDP Redundancy for Metro Interconnection

When two or more meshed VPLS instances are interconnected by redundant spoke-SDPs (as shown in Figure 63), a loop in the topology results. To remove such a loop from the topology, Spanning Tree Protocol (STP) can be run over the SDPs (links) which form the loop such that one of the SDPs is blocked. As running STP in each and every VPLS in this topology is not efficient, the node includes functionality which can associate a number of VPLSes to a single STP instance running over the redundant SDPs. Node redundancy is therefore achieved by running STP in one VPLS, and applying the conclusions of this STP to the other VPLS services. The VPLS instance running STP is referred to as the “management VPLS” or mVPLS.

In the case of a failure of the active node, STP on the management VPLS in the standby node will change the link states from disabled to active. The standby node will then broadcast a MAC flush LDP control message in each of the protected VPLS instances, so that the address of the newly active node can be relearned by all PEs in the VPLS.

It is possible to configure two management VPLS services, where both VPLS services have different active spokes (this is achieved by changing the path-cost in STP). By associating different user VPLSes with the two management VPLS services, load balancing across the spokes can be achieved.

Figure 63:  H-VPLS with Spoke Redundancy 

5.2.9.3. Inter-Domain VPLS Resiliency Using Multi-Chassis Endpoints

Note: MC-EP is not supported on 7210 SAS platforms. This section provides an example of how 7210 SAS platforms can be used as MTU devices in an MC-EP solution. In this solution, 7750 SR routers provide the MC-EP functionality.

Inter-domain VPLS refers to a VPLS deployment where sites may be located in different domains. An example of inter-domain deployment can be where different Metro domains are interconnected over a Wide Area Network (Metro1-WAN-Metro2) or where sites are located in different autonomous systems (AS1-ASBRs-AS2).

Multi-chassis endpoint (MC-EP) provides an alternate solution that does not require RSTP at the gateway VPLS PEs while still using pseudowires to interconnect the VPLS instances located in the two domains.

MC-EP expands the single chassis endpoint based on active-standby pseudowires for VPLS shown in Figure 64. In the solution depicted by the Figure 64, 7210 SAS devices are used as MTUs.

Figure 64:  H-VPLS Resiliency Based on AS Pseudowires 

The active-standby pseudowire solution is appropriate for the scenario when only one VPLS PE (MTU-s) needs to be dual-homed to two core PEs (PE1 and PE2).

5.2.10. VPLS Access Redundancy

A second application of hierarchical VPLS is using MTUs that are MPLS-enabled which must have spoke-SDPs to the closest PE node. To protect against failure of the PE node, an MTU can be dual-homed.

The following are several mechanisms that can be used to resolve a loop in an access network where 7210 SAS devices are used:

5.2.10.1. STP-Based Redundant Access to VPLS

Figure 65:  Dual-homed MTUs in Two-Tier Hierarchy H-VPLS  

In configuration shown in Figure 65, STP is activated on the MTU and two PEs to resolve a potential loop.

To remove such a loop from the topology, Spanning Tree Protocol (STP) can be run over the SDPs (links) which form the loop such that one of the SDPs is blocked. Running STP in every VPLS in this topology is not efficient as the node includes functionality which can associate a number of VPLSes to a single STP instance running over the redundant SDPs. Node redundancy is therefore achieved by running STP in one VPLS. Therefore, this applies the conclusions of this STP to the other VPLS services.

The VPLS instance running STP is referred to as the “management VPLS” or mVPLS. In the case of a failure of the active node, STP on the management VPLS in the standby node will change the link states from disabled to active. The standby node will then broadcast a MAC flush LDP control message in each of the protected VPLS instances, so that the address of the newly active node can be relearned by all PEs in the VPLS. It is possible to configure two management VPLS services, where both VPLS services have different active spokes (this is achieved by changing the path-cost in STP). By associating different user VPLSes with the two management VPLS services, load balancing across the spokes can be achieved.

In this configuration the scope of STP domain is limited to MTU and PEs, while any topology change needs to be propagated in the whole VPLS domain.

This is done by using “MAC-flush” messages defined by RFC 4762, Virtual Private LAN Services Using LDP Signaling. In the case where STP acts as a loop resolution mechanism, every Topology Change Notification (TCN) received in a context of STP instance is translated into an LDP-MAC address withdrawal message (also referred to as a MAC-flush message) requesting to clear all FDB entries except the ones learned from the originating PE. Such messages are sent to all PE peers connected through SDPs (mesh and spoke) in the context of VPLS services which are managed by the specific STP instance.

5.2.11. MAC Flush Message Processing

The previous sections described operation principle of several redundancy mechanisms available in context of VPLS service. All of them rely on MAC flush message as a tool to propagate topology change in a context of the specific VPLS. This section aims to summarize basic rules for generation and processing of these messages.

As described on respective sections, the 7210 SAS supports two types of MAC flush message, flush-all-but-mine and flush-mine. The main difference between these messages is the type of action they signal. Flush-all-but-mine requests clearing of all FDB entries which were learned from all other LDP peers except the originating PE. This type is also defined by RFC 4762 as an LDP MAC address withdrawal with an empty MAC address list.

Flush-all-mine message requests clearing all FDB entries learned from originating PE. This means that this message has exactly other effect then flush-all-but-mine message. This type is not included in RFC 4762 definition and it is implemented using vendor specific TLV.

The advantages and disadvantages of the individual types should be apparent from examples in the previous section. The description here focuses on summarizing actions taken on reception and conditions individual messages are generated.

Upon reception of MAC flush messages (regardless the type) SR-Series PE will take following actions:

The flush-all-but-mine message is generated under following conditions.

The flush-mine message is generated under following conditions.

5.2.11.1. MAC Flush with STP

A second application of Hierarchical VPLS is in the use of Multi Tenant Units (MTU). MTUs are typically not MPLS-enabled, and therefore have Ethernet links to the closest PE node (see Figure 66). To protect against failure of the PE node, an MTU could be dual-homed and therefore have two SAPs on two PE nodes. To resolve the potential loop, STP is activated on the MTU and the two PEs.

Like in the previous scenario, STP only needs to run in a single VPLS instance, and the results of the STP calculations are applied to all VPLSes on the link. Equally, the standby node will broadcast MAC flush LDP messages in the protected VPLS instances when it detects that the active node has failed.

Figure 66:  H-VPLS with SAP Redundancy 

5.2.11.3. Dual Homing to a VPLS Service

Figure 67:  Dual Homed CE Connection to VPLS 

Figure 67 shows a dual-homed connection to VPLS service (PE-A, PE-B, PE-C, PE-D) and operation in case of link failure (between PE-C and Layer 2-B). Upon detection of a link failure PE-C will send MAC-Address-Withdraw messages, which will indicate to all LDP peers that they should flush all MAC addresses learned from PE-C. This will lead that to a broadcasting of packets addressing affected hosts and relearning process in case an alternative route exists.

Note that the message described here is different from the message described in draft-ietf-l2vpn-vpls-ldp-xx.txt, Virtual Private LAN Services over MPLS. The difference is in the interpretation and action performed in the receiving PE. According the draft definition, upon receipt of a MAC-withdraw message, all MAC addresses, except the ones learned from the source PE, are flushed, This section specifies that all MAC addresses learned from the source are flushed. This message has been implemented as an LDP address message with vendor-specific type, length, value (TLV), and is called the flush-all-from-ME message.

The draft definition message is currently used in management VPLS which is using RSTP for recovering from failures in Layer 2 topologies. The mechanism described in this document represent an alternative solution.

The advantage of this approach (as compared to RSTP based methods) is that only MAC-affected addresses are flushed and not the full forwarding database. While this method does not provide a mechanism to secure alternative loop-free topology, the convergence time is dependent on the speed of the specific CE device will open alternative link (Layer 2-B switch in Figure 67) as well as on the speed PE routers will flush their FDB.

In addition, this mechanism is effective only if PE and CE are directly connected (no hub or bridge) as it reacts to physical failure of the link.

5.2.12. VPLS Service Considerations

This section describes various 7210 SAS service features and special capabilities or considerations as they relate to VPLS services.

5.3.1. BGP AD Overview

The BGP protocol establishes neighbor relationships between configured peers. An open message is sent after the completion of the three-way TCP handshake. This open message contains information about the BGP peer sending the message. This message contains Autonomous System Number (ASN), BGP version, timer information and operational parameters, including capabilities. The capabilities of a peer are exchanged using two numerical values: the Address Family Identifier (AFI) and Subsequent Address Family Identifier (SAFI). These numbers are allocated by the Internet Assigned Numbers Authority (IANA). BGP AD uses AFI 65 (L2VPN) and SAFI 25 (BGP VPLS).

5.3.2. Information Model

Following is the establishment of the peer relationship, the discovery process begins as soon as a new VPLS service instance is provisioned on the PE.

Two VPLS identifiers are used to indicate the VPLS membership and the individual VPLS instance:

To advertise this information, BGP AD employs a simplified version of the BGP VPLS NLRI where just the RD and the next 4 bytes are used to identify the VPLS instance. There is no need for Label Block and Label Size fields as T-LDP will take care of signaling the service labels later on.

The format of the BGP AD NLRI is very similar with the one used for IP VPN as shown in Figure 68. The system IP may be used for the last 4 bytes of the VSI-ID further simplifying the addressing and the provisioning process.

Figure 68:  BGP AD NLRI versus IP VPN NLRI 

Network Layer Reachability Information (NLRI) is exchanged between BGP peers indicating how to reach prefixes. The NLRI is used in the Layer 2 VPN case to tell PE peers how to reach the VSI rather than specific prefixes. The advertisement includes the BGP next hop and a route target (RT). The BGP next hop indicates the VSI location and is used in the next step to determine which signaling session is used for pseudowire signaling. The RT, also coded as an extended community, can be used to build a VPLS full mesh or a H-VPLS hierarchy through the use of BGP import or export policies.

BGP is only used to discover VPN endpoints and the corresponding far end PEs. It is not used to signal the pseudowire labels. This task remains the responsibility of targeted-LDP (T-LDP).

5.3.3. FEC Element for T-LDP Signaling

Two LDP FEC elements are defined in RFC 4447, PW Setup & Maintenance Using LDP. The original pseudowire-ID FEC element 128 (0x80) employs a 32-bit field to identify the virtual circuit ID and it was used extensively in the initial VPWS and VPLS deployments. The simple format is easy to understand but it does not provide the required information model for BGP Auto-Discovery function. To support BGP AD and other new applications a new Layer 2 FEC element, the generalized FEC (0x81) is required.

The generalized pseudowire-ID FEC element has been designed for auto discovery applications. It provides a field, the address group identifier (AGI), that is used to signal the membership information from the VPLS-ID. Separate address fields are provided for the source and target address associated with the VPLS endpoints called the Source Attachment Individual Identifier (SAII) and respectively, Target Attachment Individual Identifier (TAII). These fields carry the VSI-ID values for the two instances that are to be connected through the signaled pseudowire.

The detailed format for FEC 129 is shown in Figure 69.

Figure 69:  Generalized Pseudowire-ID FEC Element 

Each of the FEC fields are designed as a sub-TLV equipped with its own type and length providing support for new applications. To accommodate the BGP AD information model the following FEC formats are used:

5.3.4. BGP-AD and Target LDP (T-LDP) Interaction

BGP is responsible for discovering the location of VSIs that share the same VPLS membership. LDP protocol is responsible for setting up the pseudowire infrastructure between the related VSIs by exchanging service-specific labels between them.

When the local VPLS information is provisioned in the local PE, the related PEs participating in the same VPLS are identified through BGP AD exchanges. A list of far-end PEs is generated and triggers the creation, if required, of the necessary T-LDP sessions to these PEs and the exchange of the service-specific VPN labels. The steps for the BGP AD discovery process and LDP session establishment and label exchange are shown in Figure 70.

Figure 70:  BGP-AD and T-LDP Interaction 

Key:

5.3.5. SDP Usage

Service Access Points (SAP) are linked to transport tunnels using Service Distribution Points (SDP). The service architecture of the 7210 platform allows services to be abstracted from the transport network.

MPLS transport tunnels are signaled using the Resource Reservation Protocol (RSVP-TE) or by the Label Distribution Protocol (LDP). The capability to automatically create an SDP only exists for LDP based transport tunnels. Using a manually provisioned SDP is available for both RSVP-TE and LDP transport tunnels. Refer to the 7210 SAS-M, T, R6, R12, Mxp, Sx, S MPLS Guide for more information about MPLS, LDP, and RSVP.

5.3.6. Automatic Creation of SDPs

When BGP AD is used for LDP VPLS and LDP is used as the transport tunnel there is no requirement to manually create an SDP. The LDP SDP can be automatically instantiated using the information advertised by BGP AD. This simplifies the configuration on the service node.

Enabling LDP on the IP interfaces connecting all nodes between the ingress and the egress, builds transport tunnels based on the best IGP path. LDP bindings are automatically built and stored in the hardware. These entries contain an MPLS label pointing to the best next hop along the best path toward the destination.

When two endpoints need to connect and no SDP exists, a new SDP will automatically be constructed. New services added between two endpoints that already have an automatically created SDP will be immediately used. No new SDP will be constructed. The far-end information is gleaned from the BGP next hop information in the NLRI. When services are withdrawn with a BGP_Unreach_NLRI, the automatically established SDP will remain up as long as at least one service is connected between those endpoints. An automatically created SDP will be removed and the resources released when the only or last service is removed.

5.3.7. Manually Provisioned SDP

The carrier is required to manually provision the SDP if they create transport tunnels using RSVP-TE. Operators have the option to choose a manually configured SDP, if they use LDP as the tunnel signaling protocol. The functionality is the same regardless of the signaling protocol.

Creating a BGP-AD enabled VPLS service on an ingress node with the manually provisioned SDP option causes the Tunnel Manager to search for an existing SDP that connects to the far-end PE. The far-end IP information is gleaned from the BGP next hop information in the NLRI. If a single SDP exists to that PE, it is used. If no SDP is established between the two endpoints, the service remains down until a manually configured SDP becomes active.

When multiple SDPs exist between two endpoints, the tunnel manager selects the appropriate SDP. The algorithm preferred SDPs with the best (lower) metric. Should there be multiple SDPs with equal metrics, the operational state of the SDPs with the best metric is considered. If the operational state is the same, the SDP with the higher sdp-id is used. If an SDP with a preferred metric is found with an operational state that is not active, the tunnel manager flags it as ineligible and restarts the algorithm.

5.3.8. Automatic Instantiation of Pseudowires (SDP Bindings)

The choice of manual or auto provisioned SDPs has limited impact on the amount of required provisioning. Most of the savings are achieved through the automatic instantiation of the pseudowire infrastructure (SDP bindings). This is achieved for every auto-discovered VSIs through the use of the pseudowire template concept. Each VPLS service that uses BGP AD contains the “pw-template-binding” option defining specific Layer 2 VPN parameters. This command references a “pw-template” which defines the pseudowire parameters. The same “pwtemplate” may be referenced by multiple VPLS services. As a result, changes to these pseudowire templates have to be treated with great care as they may impact many customers at once.

The Nokia implementation provides for safe handling of pseudowire templates. Changes to the pseudowire templates are not automatically propagated. Tools are provided to evaluate and distribute the changes. The following command is used to distribute changes to a “pw-template” at the service level to one or all services that use that template.

PERs-4# tools perform service id 300 eval-pw-template 1 allow-service-impact

If the service ID is omitted, then all services are updated. The type of change made to the “pwtemplate” influences how the service is impacted.

Both of these changes affect the services. Other changes are not service affected.

5.3.9. Mixing Statically Configured and Auto-Discovered Pseudowires in a VPLS Service

The services implementation allows for manually provisioned and auto-discovered pseudowire (SDP bindings) to coexist in the same VPLS instance (for example, both FEC128 and FEC 129 are supported). This allows for gradual introduction of auto discovery into an existing VPLS deployment.

As FEC 128 and 129 represent different addressing schemes, it is important to make sure that only one is used at any point in time between the same two VPLS instances. Otherwise, both pseudowires may become active causing a loop that might adversely impact the correct functioning of the service. It is recommended that FEC128 pseudowire be disabled as soon as the FEC129 addressing scheme is introduced in a portion of the network. Alternatively, RSTP may be used during the migration as a safety mechanism to provide additional protection against operational errors.

5.3.10. Resiliency Schemes

The use of BGP-AD on the network side, or in the backbone, does not affect the different resiliency schemes Nokia has developed in the access network. This means that both Multi-Chassis Link Aggregation (MC-LAG) and Management-VPLS (M-VPLS) can still be used.

BGP-AD may coexist with Hierarchical-VPLS (H-VPLS) resiliency schemes (for example, dual homed MTU-s devices to different PE-rs nodes) using existing methods (M-VPLS and statically configured Active or Standby pseudowire endpoint).

If provisioned SDPs are used by BGP AD, M-VPLS may be employed to provide loop avoidance. However, it is currently not possible to auto-discover active or standby pseudowires and to instantiate the related endpoint.

5.4.1. IES or VPRN IP Interface Binding

A standard IP interface within an existing IES or VPRN service context may be bound to a service name. A VPLS service only supports binding for a single IP interface.

While an IP interface may only be bound to a single VPLS service, the routing context containing the IP interface (IES or VPRN) may have other IP interfaces bound to other VPLS service contexts. That is, R-VPLS allows the binding of IP interfaces in IES and VPRN services to be bound to VPLS services.

5.4.2. Assigning a Service Name to a VPLS Service

When a service name is applied to any service context, the name and service ID association is registered with the system. A service name cannot be assigned to more than one service ID.

Special consideration is given to a service name that is assigned to a VPLS service that has the configure service vpls allow-ip-int-binding command enabled. If a name is applied to the VPLS service while the allow-ip-int-binding flag is set, the system scans the existing IES and VPRN services for an IP interface that is bound to the specified service name. If an IP interface is found, the IP interface is attached to the VPLS service associated with the name. Only one interface can be bound to the service with the specified name.

If the allow-ip-int-binding command is not enabled on the VPLS service, the system does not attempt to resolve the VPLS service name to an IP interface. As soon as the allow-ip-int-binding flag is configured on the VPLS, the corresponding IP interface is bound and becomes operational up. There is no need to toggle the shutdown or no shutdown command.

If an IP interface is not currently bound to the VPLS service name, no action is taken at the time of the service name assignment.

5.4.3. Service Binding Requirements

In the event that a defined service name is created on the system, the system checks to ensure that the service type is VPLS. If the created service type is VPLS, the IP interface is eligible to enter the operationally upstate.

5.4.3.5. IP Interface MTU and Fragmentation

Note: VPLS service MTU is supported on all 7210 SAS platforms as described in this document, except 7210 SAS-M and 7210 SAS-T platforms operating in access-uplink mode.

The user must ensure that the port MTU is configured appropriately so that the largest packet traversing through any of the SAPs (virtual ports) of the VPLS service can be forwarded out of any of the SAPs. VPLS services do not support fragmentation and can discard packets larger than the configured port MTU.

When an IP interface is associated with a VPLS service, the IP-MTU is based on either the administrative value configured for the IP interface or an operational value derived from port MTU of all the SAPs configured in the service. The port MTU excluding the Layer 2 Header and tags for all the ports which have SAPs configured in this VPLS service are considered and the minimum value among those are computed (which is called computed MTU). The operational value of the IP interface is set as follows.

1. If the configured (administrative) value of IP MTU is greater than the computed MTU, then the operational IP MTU is set to the computed MTU.
2. If the configured (administrative) value of IP MTU is lesser than or equal to the computed MTU, then operational IP MTU is set to the configured (administrative) value of IP MTU.

5.4.4. ARP and VPLS FIB Interactions

Two address-oriented table entries are used when routing into a VPLS service. On the routing side, an ARP entry is used to determine the destination MAC address used by an IP next-hop. In the case where the destination IP address in the routed packet is a host on the local subnet represented by the VPLS instance, the destination IP address is used as the next-hop IP address in the ARP cache lookup. If the destination IP address is in a remote subnet that is reached by another router attached to the VPLS service, the routing lookup returns the local IP address on the VPLS service of the remote router is returned. If the next-hop is not currently in the ARP cache, the system generates an ARP request to determine the destination MAC address associated with the next-hop IP address. IP routing to all destination hosts associated with the next-hop IP address stops until the ARP cache is populated with an entry for the next-hop. The dynamically populated ARP entries age out according to the ARP aging timer.

The second address table entry that affects VPLS routed packets is the MAC destination lookup in the VPLS service context. The MAC associated with the ARP table entry for the IP next-hop may or may not currently be populated in the VPLS Layer 2 FIB table. While the destination MAC is unknown (not populated in the VPLS FIB), the system is flooded with all packets destined to that MAC (routed or bridged) to all SAPs within the VPLS service context. When the MAC is known (populated in the VPLS FIB), all packets destined to the MAC (routed or bridged) is targeted to the specific SAP where the MAC has been learned. As with ARP entries, static MAC entries may be created in the VPLS FIB. Dynamically learned MAC addresses are allowed to age out or be flushed from the VPLS FIB while static MAC entries always remain associated with a specific virtual port. Dynamic MACs may also be relearned on another VPLS SAP than the current SAP in the FIB. In this case, the system automatically moves the MAC FIB entry to the new VPLS SAP.

Note: In 7210 SAS, whenever a MAC entry is removed from the VPLS FIB (either explicitly by the user or due to MAC aging or mac-move), ARP entries which match this MAC address is removed from the ARP cache. Though the VPLS FIB entries are not removed; an ARP entry ages out and is removed from the ARP cache. If the VPLS FIB limit is reached and the node is no longer able to learn new MAC address, ARP will also not be learned.

5.4.5. R-VPLS Specific ARP Cache Behavior

In typical routing behavior, the system uses the IP route table to select the egress interface, an ARP entry is used forward the packet to the appropriate Ethernet MAC. With R-VPLS, the egress IP interface may be represented by multiple egress (VPLS service SAPs).

Table 53 describes how the ARP cache and MAC FIB entry states interact.

5.4.6. R-VPLS SAP Support on Standard Ethernet Ports

The allow-ip-int-binding flag is set (routing support enabled) on a VPLS service. SAPs within the service can be created on standard Ethernet ports.

5.4.7. VPLS SAP Ingress IP Filter Override

When an IP Interface is attached to a VPLS service context, the VPLS SAP provisioned IP filter for ingress routed packets may be optionally overridden to provide special ingress filtering for routed packets. This allows different filtering for routed packets and non-routed packets. The filter override is defined on the IP interface bound to the VPLS service name. A separate override filter may be specified for IPv4 packet types.

If a filter for a specific packet type (IP) is not overridden, the SAP-specified filter is applied to the packet (if defined).

Table 54 and Table 55 list ACL lookup behavior with and without Ingress Override filter attached to an IES interface in an R-VPLS service.

5.4.8. R-VPLS and IGMPv3 Snooping

Note: This feature is supported on all 7210 SAS platforms as described in this document, except those operating in access-uplink mode.

This feature (IGMPv3 snooping in R-VPLS) extends IGMP snooping to an R-VPLS service. On 7210 SAS, VPLS services that use MPLS uplinks (network mode) support IGMP snooping with IGMP v1 and v2 only. That is, IGMP v3 is not supported, which means that only Layer 2 multicast is supported. To support source-based IP multicast, support for IGMPv3 is needed. To provide source-based IP multicast, support for IGMP snooping v1, v2, and v3 is added to R-VPLS service. The IGMPv3 snooping in R-VPLS feature gives customers an option to use an R-VPLS service without a configured IP interface association to deliver IP multicast traffic in access Layer 2 networks. Users also have an option to configure MVR service.

IGMPv3 snooping in R-VPLS is supported only for IES (not for VPRNs).

For information about IGMP snooping in the context of VPLS, see IGMP Snooping in a VPLS Service.

5.4.9. R-VPLS Supported Functionality and Restrictions

R-VPLS supported functionality and restrictions for both access-uplink and network modes are listed as follows. The following items are applicable to both the modes, unless specified explicitly.

5.5.1. Epipe Emulation Configuration Guidelines and Restrictions

The VPLS service with dot1q-range SAPs uses svc-sap-type of dot1q-range and supports limited functionality in comparison to a normal VPLS service. The following list provides more information about the feature, configuration guidelines, and restrictions: