Route-Based Redundant Site-to-Site VPN to Azure (BGP over IKEv2/IPsec)

This guide shows an example of a redundant (active-active) route-based IKEv2 site-to-site VPN to Azure using VTI and BGP for dynamic routing updates.

Prerequisites

A pair of Azure VNet Gateways deployed in active-passive configuration with BGP enabled.
A local network gateway deployed in Azure representing the Vyos device, matching the below Vyos settings except for address space, which only requires the Vyos private IP, in this example 10.10.0.5/32
A connection resource deployed in Azure linking the Azure VNet gateway and the local network gateway representing the Vyos device.

Example

WAN Interface	eth0
On-premises address space	10.10.0.0/16
Azure address space	10.0.0.0/16
Vyos public IP	198.51.100.3
Vyos private IP	10.10.0.5
Azure VNet Gateway 1 public IP	203.0.113.2
Azure VNet Gateway 2 public IP	203.0.113.3
Azure VNet Gateway BGP IP	10.0.0.4,10.0.0.5
Pre-shared key	ch00s3-4-s3cur3-psk
Vyos ASN	64499
Azure ASN	65540

Vyos configuration

Configure the IKE and ESP settings to match a subset of those supported by Azure:

set vpn ipsec esp-group AZURE compression 'disable'
set vpn ipsec esp-group AZURE lifetime '3600'
set vpn ipsec esp-group AZURE mode 'tunnel'
set vpn ipsec esp-group AZURE pfs 'dh-group2'
set vpn ipsec esp-group AZURE proposal 1 encryption 'aes256'
set vpn ipsec esp-group AZURE proposal 1 hash 'sha1'

set vpn ipsec ike-group AZURE dead-peer-detection action 'restart'
set vpn ipsec ike-group AZURE dead-peer-detection interval '15'
set vpn ipsec ike-group AZURE dead-peer-detection timeout '30'
set vpn ipsec ike-group AZURE ikev2-reauth 'yes'
set vpn ipsec ike-group AZURE key-exchange 'ikev2'
set vpn ipsec ike-group AZURE lifetime '28800'
set vpn ipsec ike-group AZURE proposal 1 dh-group '2'
set vpn ipsec ike-group AZURE proposal 1 encryption 'aes256'
set vpn ipsec ike-group AZURE proposal 1 hash 'sha1'

Enable IPsec on eth0

set vpn ipsec ipsec-interfaces interface 'eth0'

Configure two VTIs with a dummy IP address each

set interfaces vti vti1 address '10.10.1.5/32'
set interfaces vti vti1 description 'Azure Primary Tunnel'

set interfaces vti vti2 address '10.10.1.6/32'
set interfaces vti vti2 description 'Azure Secondary Tunnel'

Clamp the VTI’s MSS to 1350 to avoid PMTU blackholes.

set firewall options interface vti1 adjust-mss 1350
set firewall options interface vti2 adjust-mss 1350

Configure the VPN tunnels

set vpn ipsec site-to-site peer 203.0.113.2 authentication id '198.51.100.3'
set vpn ipsec site-to-site peer 203.0.113.2 authentication mode 'pre-shared-secret'
set vpn ipsec site-to-site peer 203.0.113.2 authentication pre-shared-secret 'ch00s3-4-s3cur3-psk'
set vpn ipsec site-to-site peer 203.0.113.2 authentication remote-id '203.0.113.2'
set vpn ipsec site-to-site peer 203.0.113.2 connection-type 'respond'
set vpn ipsec site-to-site peer 203.0.113.2 description 'AZURE PRIMARY TUNNEL'
set vpn ipsec site-to-site peer 203.0.113.2 ike-group 'AZURE'
set vpn ipsec site-to-site peer 203.0.113.2 ikev2-reauth 'inherit'
set vpn ipsec site-to-site peer 203.0.113.2 local-address '10.10.0.5'
set vpn ipsec site-to-site peer 203.0.113.2 vti bind 'vti1'
set vpn ipsec site-to-site peer 203.0.113.2 vti esp-group 'AZURE'

set vpn ipsec site-to-site peer 203.0.113.3 authentication id '198.51.100.3'
set vpn ipsec site-to-site peer 203.0.113.3 authentication mode 'pre-shared-secret'
set vpn ipsec site-to-site peer 203.0.113.3 authentication pre-shared-secret 'ch00s3-4-s3cur3-psk'
set vpn ipsec site-to-site peer 203.0.113.3 authentication remote-id '203.0.113.3'
set vpn ipsec site-to-site peer 203.0.113.3 connection-type 'respond'
set vpn ipsec site-to-site peer 203.0.113.3 description 'AZURE SECONDARY TUNNEL'
set vpn ipsec site-to-site peer 203.0.113.3 ike-group 'AZURE'
set vpn ipsec site-to-site peer 203.0.113.3 ikev2-reauth 'inherit'
set vpn ipsec site-to-site peer 203.0.113.3 local-address '10.10.0.5'
set vpn ipsec site-to-site peer 203.0.113.3 vti bind 'vti2'
set vpn ipsec site-to-site peer 203.0.113.3 vti esp-group 'AZURE'

Important: Add an interface route to reach both Azure’s BGP listeners

set protocols static interface-route 10.0.0.4/32 next-hop-interface vti1
set protocols static interface-route 10.0.0.5/32 next-hop-interface vti2

Configure your BGP settings

set protocols bgp 64499 neighbor 10.0.0.4 remote-as '65540'
set protocols bgp 64499 neighbor 10.0.0.4 address-family ipv4-unicast soft-reconfiguration 'inbound'
set protocols bgp 64499 neighbor 10.0.0.4 timers holdtime '30'
set protocols bgp 64499 neighbor 10.0.0.4 timers keepalive '10'

set protocols bgp 64499 neighbor 10.0.0.5 remote-as '65540'
set protocols bgp 64499 neighbor 10.0.0.5 address-family ipv4-unicast soft-reconfiguration 'inbound'
set protocols bgp 64499 neighbor 10.0.0.5 timers holdtime '30'
set protocols bgp 64499 neighbor 10.0.0.5 timers keepalive '10'

Important: Disable connected check, otherwise the routes learned from Azure will not be imported into the routing table.

set protocols bgp 64499 neighbor 10.0.0.4 disable-connected-check
set protocols bgp 64499 neighbor 10.0.0.5 disable-connected-check