Information Technology Reference
In-Depth Information
obtains a port and can peer with anyone else at the exchange point who is interested over
that port. The public exchanges have a reputation for being highly congested and having
problems with packet loss.
Private Peering
Private peering involves two ISPs negotiating a peering agreement and establishing a
private connection between the ISPs, such as a point-to-point circuit. These two ISPs are
the only ones that peer across this circuit. The private peering model allows the ISPs to
move away from congested exchanges, providing higher-quality connectivity.
ISP Tiers and Peering
The subject of ISP tiers is very hazy unless you have a good understanding of what each
tier is. It is generally accepted that there are three tiers:
Tier 1
— Nationwide backbone
— Does not purchase any transit
— Relies completely on peering
Tier 2
— Nationwide backbone
— Combination of peering and transit
Tier 3
—Regional or local network
— Relies almost completely on transit
— Might have some peering, but often does not
The major tier 1 providers rely entirely on peering without purchasing transit. They pri-
vately peer in eight U.S. locations, called the default-free zone. These locations are New
York City, Washington D.C., Atlanta, Chicago, Dallas, Los Angeles, Seattle, and San Jose
(Bay Area).
A common sentiment about transit and peering is “Once a customer, never a peer.” You
should keep in mind this philosophy when determining where to purchase transit. After you
become a customer of a particular ISP, it is very difficult to transition to a peering
relationship with that ISP.
NOTE
 
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