Sample Scenario of H-VPLS on ACX Series Routers for IPTV Services
Hierarchical LDP-based VPLS requires a full mesh of tunnel LSPs between all the PE routers that participate in the VPLS service. For each VPLS service, n*(n-1)/2 pseudowires must be set up between the PE routers. Although the full mesh requirement creates signaling overhead, the larger negative impact to large-scale deployment is the packet replication requirements for each provisioned pseudowire on a PE router. Using hierarchical connectivity reduces signaling and replication overhead to facilitate large-scale deployments. .
In a typical IPTV solution, IPTV sources are in the public domain and the subscribers are in the private VPN domain. The objective is to deliver the multicast streams originated from the IPTV source to the set-top boxes or subscribers in the private domain. Generally, for an efficient delivery of multicast data from the IP Sources to the access devices (ACX in this case), P2MP LSPs and mVPN is used. The subscriber devices could then be connected to a VPLS or a Layer 3 VPN domain in Access router and they could be configured to import the multicast routes from an MVPN instance. Because VPLS and MVPN are not supported on ACX routers, an alternative approach can be used to achieve H-VPLS capabilities. The support for PIM snooping in Layer 3 interfaces, IGMP snooping in Layer 2 networks, IRB interfaces, and logical tunnel interfaces enables HVLS support.
An ACX router receives the multicast data on the default VRP context and the data gets forwarded on to the BD through IRB and gets replicated on the BD ports based on the membership detected through IGMP snooping. Unicast control traffic between Subscriber devices and the IPTV subscriber management server goes through the private VPN domain. Aggregation routers have VPLS full-mesh connectivity between each other and ACX works as H-VPLS MTU. There is a PW setup between ACX and the aggregation router. LT interface does the stitching of the Bridge domain with the PW
Sample Configuration Scenario of H-VPLS for IPTV Services
Consider a scenario in which set-top boxes (STBs) or customer premises equipment (CPE) devices are connected to two ACX routers, ACX1 and ACX2. On the ACX routers, a global virtual routing and forwarding (VRF) context, bridge domains, pseudowires, and IRB settings are defined. ACX1 is connected to two MX Series routers, MX2 and MX3. Connection to ACX1 to MX2 is through an active pseudowire with PIM deployed. PIM is used as the transport protocol in communication between ACX and MX routers. Unicast transmission is also configured. Connection of ACX1 to MX3 is through a backup pseudowire. ACX2 is connected to two MX Series routers, MX2 and MX3. Connection to ACX2 to MX2 is through an active pseudowire. ACX2 is linked to MX3 using a standby pseudowire. MX2 and MX3 are connected to MX1, which is the root of the LSP. MX1 is linked to an IPTV source.
Point-to-multipoint (P2MP) traffic engineering (TE) LSP is setup from the MX router (MX-1 is connected to the IPTV source) to the aggregation MX routers (MX-2 & MX-3). MX-1 is the root of the LSP. MX-2 and MX-3 are the leaves. Leaves cannot be configured statically or dynamically.
PIM can be enabled between MX-1 and IPTV Source and MX-1 is the DR for the Multicast source.
mVPN is configured on the default VRF routing instance. Selective tree can be used for optimal routing.
PIM-SM is running in the Access network between access routers (ACX-1 and ACX-2) and aggregation routers (MX-1 and MX-2).
MX-1 and MX-2 are the RPs for the PIM-SM.
RPF check is disabled for the multicast groups in aggregation routers for it to accept the data from remote source.
Rendezvous point (RP) redundancy is achieved by configuring auto-RP in ACXs and configuring multiple aggregation routers as RP for every access ring (PIM island).
ACX has a bridge-domain and subscriber devices are connected to the BD ports. This enables the subscribers to be on the same IP subnet. (This method of configuration suits a topology in which you want all the subscribers connected to the ACXs in a single access ring to be on the same subnet. This makes the DHCP server pool allocation policy easier). No local switching is enabled on the bridge domain, to ensure that subscriber to subscriber communication does not occur locally through the bridge domain.
Bridge domain has the IRB configuration providing connectivity to the default VRF router instance. IGMP is enabled on the IRB interface. This enables the IGMP join messages send by the subscriber devices to be processed by the routing module and in turn triggers a PIM join towards RP in the default routing instance.
IGMP snooping is enabled on the bridge domain for an optimal forwarding of multicast data at the BD level.
ACX router receives the multicast data on the default VRP context and the data gets forwarded on to the BD through IRB and gets replicated on the BD ports based on the membership detected through IGMP snooping.
Unicast control traffic between Subscriber devices and the IPTV subscriber management server goes through the private VPN domain.
Aggregation routers have VPLS full-mesh connectivity between each other and ACX works as H-VPLS MTU.
There is a PW set up between ACX and the aggregation router. LT interface does the stitching of the Bridge domain with the PW.
An active and a standby pseudowire are set up between ACX and aggregation routers to support redundancy for the control traffic.
PW terminates into the VPLS instance in the aggregation router. PWs from multiple ACX routers are terminated to the same VPLS instance as all the subscribers across all ACX boxes connected to a same aggregation router are in the same subnet.
VPLS instance in the aggregation router is connected to the L3VPN instance through IRB interface which has IP address from the same subnet as the subscribers. Subscriber management station that is controlling the subscribers belong to a particular customer is connected to this Layer 3 VPN domain.
Guidelines for H-VPLS on ACX Routers
Keep the following points in mind while configuring H-VPLS on ACX routers:
Control traffic is limited to 1G or 10G bandwidth based on the logical tunnel (lt-) interface limitation.
Multicast data delivery is based on PIM on the access network. Therefore, the convergence time is directly related to the convergence time of the IGP protocol configured on the access network.
Two versions of multicast solutions must be implemented in the provider network for the end-to-end solution to work. Also, you must set up PIM- based solution on the access network and MVPN-based solution on the aggregation or core network. This topology is considered a configuration overhead.
IPv6 multicast and active-active redundancy models are not supported.
You can implement an IPTV framework without the MVPN and VPLS support on ACX routers.
Multicast support using PIM-SM and IGMP is supported,
Unicast control traffic is restricted to the customer VPN domain.
Support for multiple subscribers to be on the same IP subnet is provided. Direct communication between the subscribers at the ACX level is disabled.
IGMP snooping is supported to ensure that the multicast data is not forwarded to the subscribers that are not registered for that data.
An IRB interface is used for only multicast data delivery from the default VRF context.