服务链(Service Chaining,or Service Function Chaining,SFC,功能服务链)

Software-configured  service  chaining  provides  the  capability  to  dynamically include best-of-breed functions in a network processing path.The concept is shown in Figure 1. Each circle represents a different service function (a.k.a. network function) that is connected to other services via a network.The arrows represent three different  service  chains  that  comprise  a  particular  set  of  service  functions  connected in order.

In principle, a number of different topologies are possible. For example, service path forking, service function sharing and bidirectional service chains will all be useful in different scenarios. Service chains can be fine-grained or coarse-grained, depending on the use cases, and may be either highly dynamic or based on predefined service templates.

An important principle is that the"service graph"is decoupled from the network,so the operator can configure a processing path to run across both physical and virtual components. This abstraction is fundamental because it generates an architecturethat is applicable to physical, virtualized and hybrid network contexts, and therefore makes the service chaining applicable to multiple operator types and use cases
 
 
 
 服务链(Service Chaining,or Service Function Chaining,SFC,功能服务链)
 
 

What is Network Service Chaining? Definition

Network service chaining, also known as service function chaining (SFC) is a capability that uses software-defined networking (SDN) capabilities to create a service chain of connected network services (such as L4-7 like firewalls, network address translation [NAT], intrusion protection) and connect them in a virtual chain.  This capability can be used by network operators to set up suites or catalogs of connected services that enable the use of a single network connection for many services, with different characteristics.

SDN服务链

数据报文在网络中传递时,需要经过各种各样的业务节点,才能保证网络能够按照设 计要求,提供给用户安全、快速、稳定的网络服务。当网络流量按照业务逻辑所要求的既定的顺序,经过这些业务点(主要指安全设备如防火墙、LB等),这就是 服务链(Service Chain)。服务链可以理解为一种业务形式。

1. SDN服务链

过去也有服务链的概念,但传统网络的服务链和网络拓扑紧密耦合、部署复杂,在服务链变更、扩容时,都需要改动网络拓扑,重新进行网络设备的配置。而云计算环境广泛使用虚拟化技术,具有动态性、高流动性、规模易变化、多租户等特点,传统网络的服务链无法满足这些需求,SDN的出现让服务链又焕发了生机。因此,当前再谈及服务链时,默认指的是SDN服务链。

2. 服务链的工作原理

一个服务链通常都会有入口节点和出口节点,服务链的组织顺序,和服务节点的物理拓扑无关数据报文进入服务链以后,就会按照服务链既定的顺序穿过各个 服务节点。服务链的每一个节点,都知道当前服务链的下一个服务节点在哪里,并通过Overlay网络送达到下一个服务节点处理。在服务链的最后一个节点, 也会根据数据报文最终的目的VTEP进行封装,完成报文的转发。

3. 都有哪些厂商支持该技术?

华三、思科支持服务链,实现的原理大致相同。

4. H3C服务链的特点

H3C的服务链方案是基于Overlay技术实现的,结合SDN集中控制的理论,由VCFC(VCF Controller)进行全局控制。它是支撑虚拟化、业务网络可编程的关键,具有如下特点:

  • 实现租户逻辑组网与物理组网的解耦,控制平面和网络转发平面的分离。
  • 业务资源池化,可以根据租户网络需求进行分配、部署,与业务资源物理位置解耦,打破物理拓扑的限制,为每个租户提供个性化的业务。
  • 可以实现NFV资源池的动态创建和自动化部署。
  • 实现租户的业务灵活的编排、修改,而不影响物理拓扑和其他租户。
  • 实现服务链的高可靠性(负载分担、冗余备份)以及问题定位监测等功能。

5.H3C的服务链如何部署?

通过在VCF控制器内置服务链功能模块,服务链功能模块提供北向API,供各种云管理系统使用;同时通过南向接口,管理服务节点,部署服务链。它可以管理所有的服务节点,也可以在各个节点上配置多个服务链。

6. 什么样的报文需要进入服务链处理?

数据报文是否要进入服务链,进入哪个服务链,进入服务链以后使用的Profile是什么,都是在数据报文进入Overlay网络时,根据VCF控制器下发的策略决定的。 VCF控制器会基于不同的租户应用,灵活的下发分类策略,并确保报文在服务链内各个节点间传递。

The primary advantage of network service chaining is to automate the way virtual network connections can be set up to handle traffic flows for connected services. For example, an SDN controller could take chain of services and apply them to different traffic flows depending on the source, destination or type of traffic. The SFC capability automates what traditional network administrators do when they connect up a series of physical L4-7 devices to process incoming and out coming network traffic, which may require a number of manual steps.

 
 
 
 
 
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