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NorthStar SDN WAN Controller at MPLS World Congress 2016
02.29.16

It’s only a few days until the MPLS World Congress in Paris, so I thought I’d say some words about our live demo of NorthStar, our SDN WAN Controller.

 

One of the key applications of NorthStar is the creation of diversely routed pairs of LSPs. These are used to underpin services that have high SLA requirements - if something fails along the path of one LSP, the other is unaffected and so can still carry traffic. This is illustrated in Figure 1.

 

Figure 1: are these LSPs really diverse?Figure 1: are these LSPs really diverse?

But how do we know whether the LSPs are truly diverse? - they may appear to be diverse at the IP/MPLS layer, but there may be some fate-sharing in the underlying optical layer.

 

One option is to configure Shared Risk Link Group (SRLG) tags on the interfaces on routers P1, P2, P4 and P5 that share fate. These SRLGs are carried in the IGP alongside all the other link-state information and communicated to the NorthStar via IGP or BGP-LS peering. Another option is to configure the NorthStar conroller with SRLG info via the northbound REST API. However, in the conference, I will talk about a third option: a standards-based YANG-based data model [1] that enables an optical NMS to communicate essential information about the optical layer to the NorthStar controller. This allows the optical NMS to advertise Shared Risk Link Groups (SRLGs), so that NorthStar is aware of any fate-sharing. This dynamic approach provides a higher degree of automation than manually configuring SRLGs on the router interfaces, bearing in mind that the SRLGs could change over time, for example if the routing of paths through the optical network changes over time.

 

In Figure 2, the left-hand side shows details of the underlying optical infrastructure. As can be seen, the link between P1 and P4 shares fate with the link between P2 and P5, as they use the same optical fibre between optical nodes O3 and O4.

 

Figure 2: the left-hand side shows details of the underlying optical infrastructure. The right-hand side shows the resulting set of abstract links that are advertised by the optical controller to the packet controllerFigure 2: the left-hand side shows details of the underlying optical infrastructure. The right-hand side shows the resulting set of abstract links that are advertised by the optical controller to the packet controller

The optical controller describes the connections that it provides to the client packet layer in the form of abstract links, shown on the right-hand side of the slide. Abstract links allow key information (for example SRLGs and delay metrics) to be communicated to the packet controller, while hiding information that is not of interest to it, for example intermediate optical nodes in the end-to-path.

 

Let’s look at another example, this time with screen-shots from the NorthStar GUI. In Figure 3, the upper part of the network map shows the routers. The lower part shows abstract links and nodes that have been advertised by the optical controller. The table at the bottom of the screen shows SRLGs that have been advertised by the optical controller to NorthStar. The highlighted SRLG shows that the vmx10-p12 to vmx20-p22 link and the vmx10-p11 to vmx10-p21 link share fate (shown in yellow on the map).

 

Figure 3: NorthStar knows from the information it receives from the optical controller that the two highlighted links share fateFigure 3: NorthStar knows from the information it receives from the optical controller that the two highlighted links share fate

Figure 4 shows what happens if we ask NorthStar to perform a diverse path calculation between vmx10 and vmx20, taking SRLGs into account. As can be seen, NorthStar routes one of the LSPs via vmx30-p31, so that the two LSPs are truly diverse.

 

Figure 4: A pair of diverse LSPs, taking SRLGs into accountFigure 4: A pair of diverse LSPs, taking SRLGs into account

 

If you would like to hear more, come to my talk during the conference on Friday morning. Also we will be having live demos of the scheme on our exhibition booth for the whole duration of the conference. See you in Paris!

 

Reference:

[1] draft-ietf-teas-yang-te-topo