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What to Look for in a Dial VPN Solution

Performance Considerations

Network Resiliency

In today’s competitive market,one of the

challenges service providers face as they

try to obtain and then retain customers is

keeping the network available 100 percent

of the time.More and more frequently,

customers ask providers to guarantee a

given level of uptime and impose penalties

for non-performance.Strict mean time

between failure (MTBF) standards are passed

on to network equipment suppliers.

It is critical for Dial VPNs to provide compre-

hensive solutions,which help the network

administrator to quickly diagnose errors

and implement fixes without having to

disable any equipment providing service

in real-time.

Scalability

The most desirable service accommodates

the greatest number of users while using

the least amount of equipment.Network

architecture, network equipment and net-

work management must all be scalable.

Using Layer 2 tunneling,the entire PPP

frame and its contents are transported

through the network as payload.This is

an inefficient use of available bandwidth.

(However,if end-to-end compression is

used, bandwidth is better utilized.)

Transporting the entire PPP frame also

introduces potential reliability issues since

PPP Link Control Protocol (LCP) and Network

Control Protocol (NCP) are time-sensitive.

Frequently, the endpoints of the tunnel are

separated by long distances and/or many

hops.Under these conditions,PPP connec-

tions carried over Layer 2 tunnels may be

prone to timeouts or frequent resets.

As mentioned earlier,Layer 2 tunneling

also presents potential scaling problems

for customer premise equipment.Most

CPE,including routers and file servers,

cannot scale easily to handle the number

of PPP sessions or “states” that must be

m a i ntained simultaneously to acco m m od ate

the large number of users attempting to

access corporate networks via tunneling.

Vendors offering solutions based on Layer 2

tunneling will advise customers to either

upgrade the existing equipment to

accommodate the additional demand,

or add equipment to be dedicated to the

new services.

The bottom line is this:A vendor with a

complete Dial VPN solution should offer a

choice of Layer 2 and Layer 3 tunneling.

The scalability of solutions based on Layer

2 tunneling is still questionable.

Security

Security is critically important in deploying

Dial VPNs.Dial VPNs must be secure against

a c cess by unauthori zed users.Data trave r s i n g

the public data network is vulnerable to

breaches.The network must prevent this

either directly or indirectly through accom-

modating external security devices.

Security features also govern access to

VPN services.Both subscribers,(typically

corporations and ISPs) and individual users

must be authenticated to the network.

Authenticated users must be authorized

to use various services provided by the

Dial VPN.

It is essential that an IP-based VPN provide

end-to-end data encryption between the

remote client and the home network.Layer

2 tunneling can easily accommodate

encryption schemes based on IPSEC or PPP

encryption. Since Layer 3 tunneling termi-

nates PPP at the RAS,it must use Layer 3

encryption. As IPSEC continues to evolve,

it appears it will offer the best encryption

services for Layer 3 tunneling.

Network Management

No matter how many features a service

has,or how well it performs, it is not really

viable unless it can be provisioned and

managed by the service provider.The

requirements for managing Dial VPNs are

similar to those used in managing standard

public or private data networks.There are

three key areas to examine:

• Device or Element-Level Management

• Value-Added Management Applications

• Customization

Device or Element-Level Management

It is important to understand how well

a device is instrumented for network

management.No matter how good the

management applications may be,if the

device does not support the necessary

functionality,the application may not be

very helpful.

Above all,the configuration of network

elements,such as remote access concen-

trators,gateways,switches,and routers must

be as simple and straightforward to use

as possible.Improper configuration of net-

working equipment can lead to delays in

service deployment,which,in turn,can lead

to lost revenues for the service provider.

In addition to configuration,change control

and maintenance are critical factors.Change

control and maintenance refer to the ability

of network operators to modify parameters,

implement adds/moves/changes,and

reconfigure equipment dynamically without

having to reboot or worse,bring down the

entire network.

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