LISP - OMP - BGP EVPN Interoperability - Part VIII: LISP, OMP, and BGP EVPN Comparison

 

IP reachability

 

Every Overlay Network solution requires IP reachability between edge devices via Underlay Network. This section explains the basic routing solution in Underlay Network from Campus Fabric, SD-WAN, and Datacenter Fabric perspectives. Figure 7-1 illustrates the IP reachability requirements for Campus Fabric, SD-WAN, and Datacenter Fabric.

Figure 7-1: IP Reachability Requirements.

 

Campus Fabric

 

LISP Control-Plane uses Remote Locator (RLOC) IP address in LISP Map-Registers message as a destination address when it registers its local hosts to Mapping Server. Edge devices use RLOC addresses as the destination IP address in the outer IP header for VXLAN encapsulated data packets.  Core routers route tunneled data packets based on it. These are the reasons why RLOC addresses have to be routable in Underlay Network. When an edge device sends data packets from one of its locally connected hosts to a remote host behind another edge device, it does recursive routing lookup for the destination RLOC address to find out the real next-hop. Also, the Mapping Server has to have IP reachability between all edge devices.

Datacenter Fabric

 

Leaf switches use the IP address of the Network Virtual Edge (NVE) interface as BGP next-hop in EVPN NLRI update. Other Leaf switches use it as a destination IP address in the outer IP header for VXLAN encapsulated data packets, just like edge devices in Campus Fabric use RLOC IP address. That is why NVE interface IP addresses have to be routable in Underlay Network. In addition, IP addresses which Leaf and Spine are using for iBGP peering, as well as IP addresses assigned to Multicast-RP, have to be routable.

 

SD-WAN

 

Devices in Campus and Datacenter fabrics belong to the trusted network, and that is why the Underlay Network routing architecture is quite simple. Also, we don’t have to use data encryption on LAN or DC. That is not the case with SD-WAN. Public Internet and mobile networks are pretty far from the secure network, while MPLS VPN/private APNs are secure but routing/label switching are administrated by third parties. That does not affect the IP reachability requirements. Devices connected to the same transport network have to have an IP connection between themselves. SD-WAN edge devices don’t use their System-Id in Data-Plane, which is why it is not routable in Underlay Network. Edge devices identify themselves with their System-Id in OMP TLOC (Transport Locator) route advertisement, which they send over each Transport Network. The TLOC describes the device location, just like RLOC and NVE. However, it also defines the color (Transport Network), Data-Plane encapsulation (IPSec/GRE), and Public-IP address (Transport Network uplink IP). Edge devices publish customer networks using OMP Service route advertisements. These updates describe that the next-hop is System-Id X and it is reachable via Transport Network Y. Remote edge device then checks the Public-IP address for Y/X combination from TLOC table. Besides, vSmart has to have IP reachability with all edge devices and other Control-Plane components.

Overlay Network

 

Edge devices build an Overlay Network between themselves. This simply means that sending device encapsulates the original data with the IP address that the remote device uses for network virtualization.

Figure 7-2: Virtual Network Tunneling.

Campus Fabric

 

Edge-xTRs in the LISP domain use their RLOC IP addresses as a source and destination in the outer IP header. Core devises route encapsulated data based on the destination IP address in the tunnel header. Campus Fabric uses VXLAN tunneling where the Virtual Network Identifier (VNI) is LISP Instance-Id. Edge-xTR devices use flow-based load-balancing for data packets over equal costs core uplinks.

 

Datacenter Fabric

 

VTEP/Leaf switches in the BGP EVPN domain use their NVE interface IP addresses as a source and destination in the outer IP header. Core devises route encapsulated data based on the destination IP address in the tunnel header. Datacenter Fabric solution with BGP EVPN Control-Plane also uses VXLAN tunneling where the L2VNI identifies Layer 2 segments while L3VNI identifies routing domain (VRF/Tenant). VTEP/Leaf switches use flow-based load-balancing for data packets over equal-cost core uplinks.

 

SD-WAN

 

Edge devices build IPSec/GRE tunnels for data packets between their Transport Network uplink IP addresses. Edge devices can establish tunnels with other edge devices which are directly connected to the same Transport Network. Besides, edge devices can build tunnels over different Transport Networks if there is an IP connection and the tunneling policy allows it (restrict bit not set in TLOC updates). Edge devises exchange routing updates with vSmart over DTLS tunnel. All three solutions use the same Control-Plane peering model. Edge-xTR registers and requests EID-to-RLOC mapping information to and from Mapping Server. Leaf switches exchange BGP EVPN updates with Spine switches. SD-WAN edge devices exchange routing information with vSmart.

 

Final words

 

Networks virtualization, no matter which solution we are using, tends to be quite complex. However, they all serve the same need, getting data securely and resilient from point A to B. How this goal is achieved varies between solutions. LISP uses quite a simple EID-to-RLOC mapping system to describe endpoint/prefix reachability information. BGP EVPN has its route types for hosts, prefixes, L2 Multicast, L3 Tenant routed Multicast, ESI Multi-homing, and Ingress/headend replication. OMP, in turn, uses TLOC and Service routes. Each solution uses some tunneling solution where virtual networks are identified in a solution-specific way. LISP uses Instance-Id, BGP EVPN uses L2VNI/L3VNI, and OMP uses VPN/Label binding. Connecting different solutions might feel like a nightmare but in the end, it is not so complex. I have used good old BGP IPv4 Unicast with VRF Lite solution throughout this book.

Cheers - Toni Pasanen

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