SPN Concept

SNC Connectivity - SPN Concept

Last updated 10th October, 2022

Objective

Discover the details on how to implement subnets with SPN.

Instructions

Subnet

A subnet is the smallest network object. It defines a layer-2/ethernet segment with an IPv4 prefix. It's not extendable to other SecNumCloud zones or with vRack.

SecNumCloud products are attached to subnets : they will share the same ethernet segment and the same IPv4 prefix.

The IPv4 prefix matches the following rules:

  • minimum size: /28
  • maximum size: /24
  • the 3 first IP are reserved for OVHcloud: the first one for VIP, the two others for OVHcloud routers
  • no vlan tag

A subnet can also be configured for a static route using the optional next-hop field: next-hop is the IP address of the next-hop to reach the subnet (i.e the next-hop is acting as a router, like a firewall).
Next-hop must be part of another subnet.
Subnet for static routing are limited in size (i.e not limited to /24).

SPN - SecurePrivateNetwork

SPN is the container for subnets acting like a (unique) routing instance.

Attaching subnets to SPN depends on two rules:

  • an SPN can be attached to several subnets
  • a subnet can be attached to only one SPN

SPN subnet rules

Behavior using next-hop feature:

next-hop feature

BGP configuration

BGP is required on VPN-SPN and optional in a SPN. Enabling BGP in a SPN disables VRRP configuration, meaning the first IP address of the subnet won't be reachable anymore.

  • Configuration needs an AS. This AS must be independent from the customer BGP AS to form an eBGP relation. The recommended value is in the range 64512-65534.
  • eBGP Multihop is not supported
  • With several neighbors, ECMP is automatically enabled. MED and/or AS-PATH must be tuned to have path selection.
  • Each SPN supports up to 4 BGP peers.
  • Up to 50 prefixes can be announced per BGP session.
  • For each SPN you must establish a BGP session with ‘A’ device and ‘B’ device.
  • By default, BFD is activated on all BGP sessions. This protocol is higly recommended to have a faster convergence.

Expected topology:

Topology BGP

  • SPN is configured with A.B.C.D/X subnet
  • Ra and Rb devices have their own IP address, respectively 2nd and 3rd of the subnet
  • Rc is customer routing device
  • Rc must have an eBGP session with Ra and Rb
  • Local subnet Q.R.S.T/X will be learned through BGP on devices Ra and Rb then announce to be forwarded on SPN Connector (so destinating to InterDC and/or VPN-SPN)
  • Ra and Rb devices forward announces from InterDC and/or VPN-SPN

Go further

Join our community of users on https://community.ovh.com/en/.


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