AS2 (not AS1 as before), because would not be in the routing table. AS numbers depletion and 32-bit ASNs The RFC 1771 (A Border Gateway Protocol 4 (BGP-4)) planned the coding of AS numbers on 16 bits, for 64,510 possible public AS, since ASN 64512 to 65534 were reserved for private use (0 and 65535 being forbidden). In 2011, only 15,000 AS numbers were still available, and projections were envisioning a complete depletion of available AS numbers in September 2013. RFC 6793 extends AS coding from 16 to 32 bits (keeping the 16-bit AS range 0 to 65535, and its reserved AS numbers), which now allows up to 4 billion available AS. An additional private AS range is also defined in RFC 6996 (from 4200000000 to 4294967294, 4294967295 being forbidden by RFC 7300). To allow the traversal of router groups not able to manage those new ASNs, the new attribute AS4_PATH (optional transitive) is used. 32-bit ASN assignments started in 2007. Load balancing Another factor causing this growth of the routing table is the need for load balancing of multi-homed networks. It is not a trivial task to balance the inbound traffic to a multi-homed network across its multiple inbound paths, due to limitation of the BGP route selection process. For a multi-homed network, if it announces the same network blocks across all of its BGP peers, the result may be that one or several of its inbound links become congested while the other links remain under-utilized, because external networks all picked that set of congested paths as optimal. Like most other routing protocols, BGP does not detect congestion. To work around this problem, BGP administrators of that multihomed network may divide a large contiguous IP address block into smaller blocks and tweak the route announcement to make different blocks look optimal on different paths, so that external networks will choose a different path to reach different blocks of that multi-homed network. Such cases will increase the number of routes as seen on the global BGP table. One method growing in popularity to address the load balancing issue is to deploy BGP/LISP (Locator/Identifier Separation Protocol) gateways within an Internet exchange point to allow ingress traffic engineering across multiple links. This technique does not increase the number of routes seen on the global BGP table. Security By design, routers running BGP accept advertised routes from other BGP routers by default. This