Introduction

Network administrators are faced with a great challenge while selecting the Public IP address space to be used on newly provisioned Internet link. The IP address space has to be one of the following –

(1) Provider Aggregatable (PA)

(2) Provider Independent (PI)

PA (Provider Aggregatable) address assignments made by a Provider and come from a large block allocated to a Provider by RIPE.

PI (Provider Independent) addresses are individually assigned, do not have a specific provider relation and are always routed independently on the global Internet by themselves as a separate block.

While designing, an experienced mind can be life saver because the IP address space selection will depend on many factors like –

• Internet failover scenarios (Multi homing)
• Web facing and Internet browsing application requirements
• Internet Link Failover approach.

PI vs PA : Comparison Table

Below table will help give insight how both differ:

PARAMETER	PA (PROVIDER AGGREGATABLE)	PI (PROVIDER INDEPENDENT)
Ownership	Service Provider	Customer
IP pool announcement	Only can be advertised by Service provider owning the Address Pool	Can be advertised by customer through any service provider through BGP
BGP Based routing	BGP may not be required for providing redundant connectivity	BGP is one of majorly used routing option for providing redundancy
Address Block Size	Can be longer IP block of /25 or /26	At least /24 IP Block size
IP address Assignment	PA addresses are assigned from an LIR’s allocation and are registered in the RIPE Database by the LIR	PI address space is assigned separately and not from an LIR’s PA allocation. All PI assignments are registered in the RIPE Database by the RIPE NCC at the time they are assigned
Management	Easier to implement and control. NAT configuration can do the trick.	Complex BGP based routing required for traffic control and providing redundancy
Route aggregation and CIDR at provider end	Possible and this provides flexibility to service provider.	Not possible
Portability	Needs to be changed when moving from one service provider to another	Don’t need to be changed when moving from one service provider to another
Commercials	Cost cheaper than PI address block.	Costlier than PA address block.