VPN server for remote clients using IKEv2 split VPN
Split VPN is the term used to indicate you only want to use the VPN connection to reach one or more remote subnets. In order words, this type of VPN disables the "send all traffic through the VPN".
The configuration is basically the same as for VPN server for remote clients using IKEv2 except now we indicate with leftsubnet= on the VPN server what the subnet is that we are giving access to. The easiest way to ensure that the clients can reach the subnet involved is to give them an address from that subnet and enable proxy arp. For example, say you want clients to reach the remote 10.10.0.0/16 network via the VPN server at IP 188.8.131.52. You grab 10.10.20.0/24 as the range for the VPN clients. Then you configure the connection as follows (this example assumes certificates):
conn access-vpn authby=rsasig ikev2=insist # support Apple and Windows at the same time ike=aes256-sha2_512;modp2048,aes128-sha2_512;modp2048,aes256-sha1;modp1024,aes128-sha1;modp1024 esp=aes_gcm256-null,aes_gcm128-null,aes256-sha2_512,aes128-sha2_512 auto=add rekey=no # fill in with your VPN server IP left=184.108.40.206 leftcert=yourcert leftsendcert=always leftid=@yourFQDN leftsubnet=10.10.0.0/16 rightaddresspool=10.10.20.1-10.10.20.254 right=%any rightca=%same # make cisco clients happy cisco-unity=yes # address of your internal DNS server modecfgdns=10.10.10.10 leftxauthserver=yes rightxauthclient=yes leftmodecfgserver=yes rightmodecfgclient=yes modecfgpull=yes dpddelay=9m dpdtimeout=30m dpdaction=clear fragmentation=yes # if you want an ipsec0 interface using VTI vti-interface=ipsec0 vti-shared=yes vti-routing=yes mark=20/0xffffffff
And don't forget to enable proxyarp on the VPN server's internal interface. If this is eth1, add to /etc/sysctl.conf (or equivalent file in /etc/sysctl.d/)
# eth1 is the internal interface with a 10.10.X.Y/16 IP address net.ipv4.conf.eth1.proxy_arp=1