traditional router-based networks connect customer sites through routers connected via dedicated POINT-TO-POINT links (leased lines)
Leased lines advantages
complete secure, high bandwidth, superior quality, reliable
Leased lines disadvantages
Expensive
Permanent physical connection
not scalable – it is very difficult for SP to provide separate physical connection for every customer sites.
VPN networks
VPNs replaced dedicated point-to-point links with emulated point-to-point links that share common infrastructure. Customers use VPNs primarily to reduce their operational costs. Note we are speaking about VPN in general so this include also technologies like frame relay.
Example of VPN netwoks are: X.25, Frame relay, ATM, GRE, DMVPN, IPSec, MPLS, L2TPv3
you connect your sites to SP but now SP will not create for you physical point-to-point connection but virtual point-to-point connection via physical links shared among more SP customers.
this is very good cost effective, scalable solution
Advantages of VPNs
cost savings – much cheaper than leased lines
scalable – adding a new branch office is very fast and simple
similar security – you can use encryption and authentication. This will ensure you that it is as secure as leased lines
similar performance – performance is equivalent to leased lines
VPN Basic Terminology
Provider network – the service provider infrastructure used to provide VPN services
Customer network – the part of the network still under customer control
Customer site – part of the customer network
P device – the device in the provider network with no customer connectivity (SP CORE devices)
PE device – the device in the provider network to which the customer devices are connected. It can be connected to multiple customers
CE device – the device int the customer network that links to the provider network (sometimes called CPE)
PE-CE link – a link between a PE router and a CE router