Virtual Private Network (VPN) Chapter 9: Network Requirements and Preparation
All the components of your ShoreTel 8 system must exist in the same enterprise private
network. VPNs can be used to bridge your private networks across the Internet so that the
networks for two buildings are both part of the same private network. For multiple
locations that share a private network, bandwidth calculations should include the effective
bandwidth inside the private network, rather than the raw bandwidth.
Tunneling encapsulates one type of data packet into the packet of another protocol.
Multiple tunneling protocols are used today on the market:
•PPTP (Point-to-Point Tunneling Protocol): PPTP includes compression and
encryption techniques. This protocol was introduced by Microsoft to support
secure dial-up access for its desktop, which corresponds to a large share of the
•L2F (Layer 2 Forwarding): Introduced by Cisco Systems, L2F was primarily used
to tunnel traffic between two Cisco routers. It also allows IPX traffic to tunnel over
an IP WAN.
•L2TP (Layer 2 Tunneling Protocol): L2TP is an extension the PPP (Point-to-Point
Protocol) that merges the best features of L2F and PPTP. L2TP is an emerging IETF
(Internet Engineering Task Force) standard.
•IPSEC: This is a collection of security protocols from the Security Working Group
of the IETF. It provides ESP (Encapsulating Security Payload), AH (Authentication
Header), and IKE (Key Exchange Protocol) support. This protocol, mature but still
technically in a draft format, is currently considered the standard for encryption
and tunneling support in VPNs.
For PPTP, IP VPN tunneling adds another dimension to the tunneling. Before encapsulation
takes place, the packets are encrypted so that the data is unreadable to outsiders. Once the
encapsulated packets reach their destination, the encapsulation headers are separated, and
packets are decrypted and returned to their original format.
Figure 9-1 VPN Topology