SDA – Underlay Network – PnP/IS-IS

Note – According to Cisco Webinars, the underlay is already built in the CCIE Lab.

Manual:

• Overlay can run over any type of underlay.
  • Can be Layer 2 or Layer 3
    • Highly recommended layer 3.
      • ‘Lean and Mean’ underlay.
    • Spanning Tree is still needed if layer 2 is used as underlay.
• Routing Protocol
  • Cisco recommends IS-IS.
  • Can be different routing protocol, commonly using different routing protocol if brown field.
  • SD-Access supports EIGRP, OSPF, and IS-IS.
  • Each edge device must advertise loopback interfaces into underlay.
    • Loopbacks are used to form VXLAN tunnels.
  • Shared Services
    • DHCP, DNS, Domain Services, DNA Center, WLC.
    • These services sit outside of fabric domain.
      • Underlay needs to be routable to shared services.
        • ie. to internal border node.
        • 0.0.0.0/0 will not work unless internal and external border node are same device.
• MTU
  • VXLAN requires an extra 50B for header.
    • 54B if there’s a VLAN tag.
  • Cisco Recommends MTU of 9100B for the entire underlay.
    • Can be devices not running as edge or border node
      • Middle ‘routing’ devices such as older switches just passing traffic.
• Underlay link connectivity
  • P2P links between each switch in underlay.
  • Recommends 10Gbps of throughput between each switch.
• TIMERS
  • DO NOT CHANGE IGP TIMERS.
  • Use BFD to improve failure detection.

None of this is necessary if Greenfield – use LAN automation with factory default IOS-XE switches. LAN Automation will build out IS-IS underlay.LAN Automation

LAN Automation:

• Initial task is running discovery to import a Border node into inventory.
  • Once a border node is added to inventory, DNA can hop from the border node into neighboring devices to auto configure underlay.
  • Note – ‘ip routing’ needs to be configured on seed/border node before starting LAN automation.
    • Border is actually behind the scenes configuring itself as a DHCP server, handing out leases to other fabric devices, and then configuring them.
    • In addition the configurations are done with a PnP agent on the un-configured devices.
      • The additional fabric devices need to be completely factory reset.
      • Last button is ‘Stop Automation’.
        • Counter intuitive.