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VPN Service Technical Details

This page gives some technical details of the IT Services VPN Service to help in the configuration of firewalls and third-party clients.

1. Firewalls

VPN clients contact the VPN servers in the netblock

VPN clients will be given an IP address from the private IP ranges of , , or (previously or These private addresses will be mapped to a public IP in the netblock by the use of dynamic PAT.

The protocols and ports used will depend on whether you are using the older Cisco VPN client, the newer AnyConnect client or a 3rd party or native client.

The Cisco VPN client can operate in one of three transport modes. The client needs access to the following protocols and ports. These details are also relevant to most native clients capable of connecting to the IT Services VPN Service including the OS X native VPN client and clients on iPhone, iPod touch and iPad, as well as many 3rd party clients.

Transport Mode Protocols/Ports
IPSec ESP (IP protocol 50), UDP port 500
IPSec/TCP TCP port 10000
IPSec/UDP UDP ports 500, 10000

The Cisco AnyConnect VPN client requires an SSL tunnel and optionally a DTLS tunnel.

Tunnel Protocols/Ports
SSL TCP port 443
DTLS UDP port 443

2. Clients

There is nothing that inherently stops clients other than the Cisco VPN client from connecting to the IT Services VPN Service. For example, the open-source vpn client vpnc works well. However, many vendors choose not to support the protocols needed.

The following parameters may help in the configuration of a third-party IPSec client.

Parameter Value
Server platform Cisco ASA 5500 series
Server hostname
Transport mode IPSec, IPSec/TCP or IPSec/UDP
Authentication mode IKE Extended Authentication (Xauth)
IPSec group name oxford
IPSec group password See the IPSec secret in this document.
Xauth username your Remote Access username
Xauth password your Remote Access password

The following IKE proposals are supported.

Authentication Algorithm Encryption Algorithm Diffie-Hellman Group
MD5/HMAC-128 3DES-168 Group 2
MD5/HMAC-128 3DES-168 Group 5
SHA/HMAC-160 AES-128 Group 2

The service does not allow split tunnelling by VPN clients.


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Written by IT Services. Latest revision 6 April 2020