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SD-WAN & SD-Access Solutions

March 16th, 2020 in ENCOR 350-401 Go to comments

Quick summary:

Three major building blocks that make up SDA: the control plane, the data plane and the policy plane.

SD-Access
+ Control-Plane based on LISP
+ Data-Plane based on VXLAN
+ Policy-Plane based on TrustSec

Question 1

Explanation

There are five basic device roles in the fabric overlay:
+ Control plane node: This node contains the settings, protocols, and mapping tables to provide the endpoint-to-location (EID-to-RLOC) mapping system for
the fabric overlay.
+ Fabric border node: This fabric device (for example, core layer device) connects external Layer 3 networks to the SDA fabric.
+ Fabric edge node: This fabric device (for example, access or distribution layer device) connects wired endpoints to the SDA fabric.
+ Fabric WLAN controller (WLC): This fabric device connects APs and wireless endpoints to the SDA fabric.
+ Intermediate nodes: These are intermediate routers or extended switches that do not provide any sort of SD-Access fabric role other than underlay services.

SD_Access_Fabric.jpg

Reference: CCNP and CCIE Enterprise Core ENCOR 350-401 Official Cert Guide

Question 2

Explanation

The major components of the vSmart controller are:

+ Control plane connections – Each vSmart controller establishes and maintains a control plane connection with each vEdge router in the overlay network. (In a network with multiple vSmart controllers, a single vSmart controller may have connections only to a subset of the vEdge routers, for load-balancing purposes.) Each connection, which runs as a DTLS tunnel, is established after device authentication succeeds, and it carries the encrypted payload between the vSmart controller and the vEdge router. This payload consists of route information necessary for the vSmart controller to determine the network topology, and then to calculate the best routes to network destinations and distribute this route information to the vEdge routers. The DTLS connection between a vSmart controller and a vEdge router is a permanent connection. The vSmart controller has no direct peering relationships with any devices that a vEdge router is connected to on the service side (so answer C is not correct as vSmart only manages vEdge routers only, not the whole nodes within SD-WAN fabric).

+ OMP (Overlay Management Protocol) – The OMP protocol is a routing protocol similar to BGP that manages the Cisco SD-WAN overlay network. OMP runs inside DTLS control plane connections and carries the routes, next hops, keys, and policy information needed to establish and maintain the overlay network. OMP runs between the vSmart controller and the vEdge routers and carries only control plane information. The vSmart controller processes the routes and advertises reachability information learned from these routes to other vEdge routers in the overlay network.

+ Authentication – The vSmart controller has pre-installed credentials that allow it to authenticate every new vEdge router that comes online (-> Answer A is correct). These credentials ensure that only authenticated devices are allowed access to the network.

+ Key reflection and rekeying – The vSmart controller receives data plane keys from a vEdge router and reflects them to other relevant vEdge routers that need to send data plane traffic.

+ Policy engine – The vSmart controller provides rich inbound and outbound policy constructs to manipulate routing information, access control, segmentation, extranets, and other network needs.
+ Netconf and CLI – Netconf is a standards-based protocol used by the vManage NMS to provision a vSmart controller. In addition, each vSmart controller provides local CLI access and AAA.

Reference: https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/sdwan-xe-gs-book/system-overview.html

Question 3

Explanation

The southbound protocol used by APIC is OpFlex that is pushed by Cisco as the protocol for policy enablement across physical and virtual switches.

Southbound interfaces are implemented with some called Service Abstraction Layer (SAL), which talks to the network elements via SNMP and CLI.

Note: Cisco OpFlex is a southbound protocol in a software-defined network (SDN).

Question 4

Explanation

Today the Dynamic Network Architecture Software Defined Access (DNA-SDA) solution requires a fusion router to perform VRF route leaking between user VRFs and Shared-Services, which may be in the Global routing table (GRT) or another VRF. Shared Services may consist of DHCP, Domain Name System (DNS), Network Time Protocol (NTP), Wireless LAN Controller (WLC), Identity Services Engine (ISE), DNAC components which must be made available to other virtual networks (VN’s) in the Campus.

Reference: https://www.cisco.com/c/en/us/support/docs/cloud-systems-management/dna-center/213525-sda-steps-to-configure-fusion-router.html

Question 5

Explanation

Fabric mode APs continue to support the same wireless media services that traditional APs support; apply AVC, quality of service (QoS), and other wireless policies; and establish the CAPWAP control plane to the fabric WLC. Fabric APs join as local-mode APs and must be directly connected to the fabric edge node switch to enable fabric registration events, including RLOC assignment via the fabric WLC. The fabric edge nodes use CDP to recognize APs as special wired hosts, applying special port configurations and assigning the APs to a unique overlay network within a common EID space across a fabric. The assignment allows management simplification by using a single subnet to cover the AP infrastructure at a fabric site.

Reference: https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Campus/sda-sdg-2019oct.html

Question 6

Explanation

The tunneling technology used for the fabric data plane is based on Virtual Extensible LAN (VXLAN). VXLAN encapsulation is UDP based, meaning that it can be forwarded by any IP-based network (legacy or third party) and creates the overlay network for the SD-Access fabric. Although LISP is the control plane for the SD-Access fabric, it does not use LISP data encapsulation for the data plane; instead, it uses VXLAN encapsulation because it is capable of encapsulating the original Ethernet header to perform MAC-in-IP encapsulation, while LISP does not. Using VXLAN allows the SD-Access fabric to support Layer 2 and Layer 3 virtual topologies (overlays) and the ability to operate over any IP-based network with built-in network segmentation (VRF instance/VN) and built-in group-based policy.

Reference: CCNP and CCIE Enterprise Core ENCOR 350-401 Official Cert Guide

Question 7

Question 8

Explanation

The primary components for the Cisco SD-WAN solution consist of the vManage network management system (management plane), the vSmart controller (control plane), the vBond orchestrator (orchestration plane), and the vEdge router (data plane).

+ vManage – This centralized network management system provides a GUI interface to easily monitor, configure, and maintain all Cisco SD-WAN devices and links in the underlay and overlay network.

+ vSmart controller – This software-based component is responsible for the centralized control plane of the SD-WAN network. It establishes a secure connection to each vEdge router and distributes routes and policy information via the Overlay Management Protocol (OMP), acting as a route reflector. It also orchestrates the secure data plane connectivity between the vEdge routers by distributing crypto key information, allowing for a very scalable, IKE-less architecture.

+ vBond orchestrator – This software-based component performs the initial authentication of vEdge devices and orchestrates vSmart and vEdge connectivity. It also has an important role in enabling the communication of devices that sit behind Network Address Translation (NAT).

+ vEdge router – This device, available as either a hardware appliance or software-based router, sits at a physical site or in the cloud and provides secure data plane connectivity among the sites over one or more WAN transports. It is responsible for traffic forwarding, security, encryption, Quality of Service (QoS), routing protocols such as Border Gateway Protocol (BGP) and Open Shortest Path First (OSPF), and more.

Reference: https://www.cisco.com/c/dam/en/us/td/docs/solutions/CVD/SDWAN/CVD-SD-WAN-Design-2018OCT.pdf

Comments
  1. Ciscolad
    March 18th, 2020

    Question 7

    Which description of an SD-Access wireless network infrastructure deployment is true?
    A. The access point is part of the fabric underlay
    B. The WLC is part of the fabric underlay
    C. The access point is part the fabric overlay
    D. The wireless client is part of the fabric overlay

    Should be C. The access point is part the fabric overlay? correct?

  2. brad
    March 19th, 2020

    I don’t think so, an AP can’t be part of the overlay.
    Take a look at the OCG. You have to study all the topic before ….

  3. brad
    March 19th, 2020

    Sorry Ciscolad,

    I think you are right : Access Points
     AP is directly connected to FE (or to an extended node switch)
     AP is part of Fabric overlay
     AP belongs to the INFRA_VN which is mapped to the global routing
    table (new in DNAC 1.1)
     AP joins the WLC in Local mode

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