AS5400 BT

AS5400 is BT's international IP backbone, the network behind BT.net and BT's

global network services business. It is the carrier-side network, distinct from

BT's UK consumer and broadband ASNs.

What it's used for

• IP transit and global connectivity for BT's enterprise, wholesale and carrier customers across Europe, North America and Asia.
• Peering with thousands of other networks at major exchanges; the ASN sits near the top of transit-ranking tables.
• Backbone for BT's managed WAN, MPLS and internet products sold outside the UK consumer market.

Notable

• Carrier address, not eyeball address: hosts on AS5400 are far more likely to be enterprise sites, corporate edge routers and infrastructure than home broadband subscribers. BT's UK retail broadband is announced from a separate ASN.
• BT's internet capability is deliberately split by role — a European/global backbone (this ASN), a UK network, and in-country networks in several other European markets. Attributing traffic on AS5400 to "BT home users" is a common mistake.

Interesting

• The network grew out of BT's late-1990s/2000s continental fibre build and the IP business that was branded BT Ignite before becoming BT Global Services.