1-5 Intra-AS - MDT using PIM-SSM

网络技术视频分享 老车 [e-mail]

远离应试培训，提高专业素质。

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

■视频名称：

    《1-5 Intra-AS - MDT using PIM-SSM》

■所属专辑：

    《Developing Interdomain Multicast Networks》（跨域组播）

■视频时长：

    23分12秒

■内容简介：

    组播VPN原理

    组播VPN（Multicast VPN，MVPN）允许电信运营商在MPLSVPN环境中配置和提供组播服务。MVPN支持针对VRF的组播路由和转发，并且支持VRF的组播流量流经运营商骨干。

    组播域

    MVPN在VPN的路由转发表中引入了组播路由信息。当PE从CE接收了组播流量或组播控制信息时，PE根据VPN的组播路由转发表进行转发。MVPN不适用标签交换。MVPN的多个VRF可以使用组播通信，称为组播域。

    组播分发树

    MVPN为每个组播域建立一个静态默认MDT（组播分发树，Multicast Distribution Tree）。默认MDT定义了PE之间为了支持MVPN而采用的组播分发路径。如果核心网采用SSM，则采用SSM来构建默认MDT。

    MVPN还可以为大流量组播数据动态创建MDT，称为数据MDT（Data MDT）。数据MDT是思科IOS的特性。PE每秒检查一次MVPN的组播流量，如果超过门限值，那么通过UDP封装控制信息为该组播流量建立独立的SPT。从默认MDT向数据MDT切换，最快3秒，最慢13秒。数据MDT与SSM有些类似，每个VPN只生成（S，G），而不是（*，G）。

    组播隧道接口

    组播VRF与MDT的接口，称为组播隧道接口。从组播VRF的角度看，组播隧道接口是进入MDT的通道；从MDT的角度看，组播流量从MDT进入组播VRF必须经过组播隧道接口。

    支持组播VPN的BGP

    在单自治域中，如果核心网使用PIM-SM部署默认MDT，那么连接数据源的PE通过Source Registration向RP注册，然后RP向该PE建立SPT；连接接收者的PE向RP发送（*，G），建立RPT。如果默认MDT部署在PIM-SSM网络中，那么连接接收者的PE必须得知数据源PE的信息，且没RP的协助。这样，接收PE才可以向源PE发送（S，G）而建立SPT。但是，接收PE如何得知源PE的信息呢？？解决方案是源PE通过IPv4 MDT BGP向接收PE发送自身的信息。

■Abstract：

    Multicast VPN Operation

    MVPN IP allows a service provider to configure and support multicast traffic in a Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) environment. This feature supports routing and forwarding of multicast packets for each individual VPN routing and forwarding (VRF) instance, and it also provides a mechanism to transport VPN multicast packets across the service provider backbone.

    Multicast Domains

    MVPN introduces multicast routing information to the VPN routing and forwarding table. When a provider edge (PE) router receives multicast data or control packets from a customer edge (CE) router, forwarding is performed according to the information in the Multicast VPN routing and forwarding instance (MVRF). MVPN does not use label switching. A set of MVRFs that can send multicast traffic to each other constitutes a multicast domain.

    Multicast Distribution Trees

    MVPN establishes a static default MDT for each multicast domain. The default MDT defines the path used by PE routers to send multicast data and control messages to every other PE router in the multicast domain. If Source Specific Multicast (SSM) is used as the core multicast routing protocol, then the multicast IP addresses used for the default and data multicast distribution tree (MDT) must be configured within the SSM range on all PE and P routers.

    MVPN also supports the dynamic creation of MDTs for high-bandwidth transmission. Data MDTs are a feature unique to Cisco IOS software. Data MDTs are intended for high-bandwidth sources such as full-motion video inside the VPN to ensure optimal traffic forwarding in the MPLS VPN core. The threshold at which the data MDT is created can be configured on a per-router or a per-VRF basis. When the multicast transmission exceeds the defined threshold, the sending PE router creates the data MDT and sends a User Datagram Protocol (UDP) message, which contains information about the data MDT to all routers on the default MDT. The statistics to determine whether a multicast stream has exceeded the data MDT threshold are examined once every second. After a PE router sends the UDP message, it waits 3 more seconds before switching over; 13 seconds is the worst case switchover time; 3 seconds is the best case. Data MDTs are created only for (S, G) multicast route entries within the VRF multicast routing table. They are not created for (*, G) entries regardless of the value of the individual source data rate.

    Multicast Tunnel Interface

    An MVRF, which is created per multicast domain, requires the router to create a tunnel interface from which all MVRF traffic is sourced. A multicast tunnel interface is an interface the MVRF uses to access the multicast domain.

    BGP Advertisement Methods for Multicast VPN Support

    In a single autonomous system, if the default MDT for an MVPN is using PIM sparse mode (PIM-SM) with a rendezvous point (RP), then PIM is able to establish adjacencies over the Multicast Tunnel Interface (MTI) because the source PE and receiver PE discover each other through the RP. In this scenario, the local PE (the source PE) sends register messages to the RP, which then builds a shortest-path tree (SPT) toward the source PE. The remote PE, which acts as a receiver for the MDT multicast group, then sends (*, G) joins toward the RP and joins the distribution tree for that group. However, if the default MDT group is configured in a PIM Source Specific Multicast (PIM-SSM) environment rather than a PIM-SM environment, the receiver PE needs information about the source PE and the default MDT group. This information is used to send (S, G) joins toward the source PE to build a distribution tree from the source PE (without the need for an RP). The source PE address and default MDT group address are sent using BGP.