New to SD-WAN what are good first resources to learn - Also how does it work with BGP

[romanroma]

I have been reading about SD-WAN and the intelligent way to select the best path depending on application requirements. However, how does with work with inbound paths when using BGP and the inbound path is being selected by the ISP?

For example - my company has two ISP, which I only receive the default route via BGP and are equally valued. However, I have noticed that one ISP is preferred over the the other. When that one preferred ISP is active, all inbound paths from 'looking glasses' show that ISP the best path in.

Due to the latter, if SD-WAN selects the best path for latency, etc - is this in a bidirectional way, so how does the return traffic know to return the same path for best effect? Or - is the ISP already providing the best return path to me, since it is already selecting the best path?

If you also have resources and documentation for beginners in SD-WAN please point me in the best direction, since I am new to SD-WAN and want to find out what it can provide.

I have already found 'vsmart, vmanage and vbond'; however, I am not sure in a simple overview where these components are located on the network topology. In addition, if my company already uses broadband connections, does SD-WAN buy me anything? With that being said - my company does use a lot of office365 and VOIP technologies.

Thank you

Roman

[elesani]

Hi Roman,

To avoid any confusion, it's always recommended to avoid any complexity in the underlay network and leave all routing decisions to the Fabric control plane. Having said that, in your given scenario, I recommend you to deeply an ECMP model so that your BGP speaker will receive two routes with the same weight and preference. In that case, you will be in full control of the fabric control plane for routing decisions. 

However, Cisco SD-WAN Fabric is absolutely flexible with asymmetric routing path. Bear in mind that from Fabric perspective - consider CEF table for Edge router, the Next Hop for a given branch would be always the TLOC IP of the destination (would be equal to the System IP of that branch router) as a result even asymmetric return path would be simply acceptable. 

Regarding where to start with Cisco SD-WAN, Cisco Live documents would be a good start.

Hope I covered your question.

Regards,

Ehsan

[romanroma]

@elesani

"To avoid any confusion, it's always recommended to avoid any complexity in the underlay network and leave all routing decisions to the Fabric control plane. Having said that, in your given scenario, I recommend you to deeply an ECMP model so that your BGP speaker will receive two routes with the same weight and preference. In that case, you will be in full control of the fabric control plane for routing decisions. "

I already have removed prepend and use the standard weight for both my routes, and receive to default routes via the ISP by BGP; however, I will need to review on which one is actually getting used for outbound traffic.

The previous engineer, used static routes and prepend; however, dynamic fail over was not seamless since he used static routes for default outbound. In addition, I noticed that our ISP was not honoring the prepend. Due to the latter two items, I thought it was best to let BGP and the Internet do its magic.

I do not understand what you mean by "fabirc control plane" - can you give more details?

[elesani]

To elaborate more on what you questioned, by fabric control-plane I'm pointing to the role of vSmart controllers here. In your scenario, if you deal with an underlay that is providing a fair weighted path / redundant path, it will be up to vSmart controller to address routing decisions and/or apply traffic steering otherwise, although your fabric overlay will pick a TLOC and transport interface to carry the traffic, underlay can mess everything up.