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.
- Highly recommended layer 3.
- Can be Layer 2 or Layer 3
- 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.
- Underlay needs to be routable to shared services.
- 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.
- Can be devices not running as edge or border node
- VXLAN requires an extra 50B for header.
- 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.