Документ: http://tools.ietf.org/html/rfc4893
Сейчас практически на всем новом оборудовании номера автономок 32-битные (вместо ранее использовавшихся 16-битных с приватными номерами от 64512 до 65535). Используется все это ажно с 2008 года.
О правилах передачи номеров в атрибутах апдейтов:
...
4.1. Interaction Between NEW BGP Speakers
A BGP speaker that supports 4-octet Autonomous System numbers SHOULD
advertise this to its peers using the BGP Capability Advertisements.
A BGP speaker that advertises such capability to a particular peer,
and receives from that peer the advertisement of such capability MUST
encode Autonomous System numbers as 4-octet entities in both the
AS_PATH and the AGGREGATOR attributes in the updates it sends to the
peer, and MUST assume that these attributes in the updates received
from the peer encode Autonomous System numbers as 4-octet entities.
The new attributes, AS4_PATH and AS4_AGGREGATOR SHOULD NOT be carried
in the UPDATE messages between NEW BGP peers. A NEW BGP speaker that
receives the AS4_PATH and AS4_AGGREGATOR path attributes in an UPDATE
message from a NEW BGP speaker SHOULD discard these path attributes
and continue processing the UPDATE message.
4.2. Interaction Between NEW and OLD BGP Speakers
4.2.1. BGP Peering
Note that peering between a NEW BGP speaker and an OLD one is
possible only if the NEW BGP speaker has a 2-octet AS number.
However, this document does not assume that an Autonomous System with
NEW speakers has to have a globally unique 2-octet AS number --
AS_TRANS could be used instead (even if a multiple Autonomous System
would use it).
...
Из настроек Циски:
hostname (config)#router bgp ?
<1-4294967295> Autonomous system number
<1.0-XX.YY> Autonomous system number
Про записи второго asdot вида рассказывают тут: http://tools.ietf.org/html/rfc5396
Сейчас практически на всем новом оборудовании номера автономок 32-битные (вместо ранее использовавшихся 16-битных с приватными номерами от 64512 до 65535). Используется все это ажно с 2008 года.
О правилах передачи номеров в атрибутах апдейтов:
...
4.1. Interaction Between NEW BGP Speakers
A BGP speaker that supports 4-octet Autonomous System numbers SHOULD
advertise this to its peers using the BGP Capability Advertisements.
A BGP speaker that advertises such capability to a particular peer,
and receives from that peer the advertisement of such capability MUST
encode Autonomous System numbers as 4-octet entities in both the
AS_PATH and the AGGREGATOR attributes in the updates it sends to the
peer, and MUST assume that these attributes in the updates received
from the peer encode Autonomous System numbers as 4-octet entities.
The new attributes, AS4_PATH and AS4_AGGREGATOR SHOULD NOT be carried
in the UPDATE messages between NEW BGP peers. A NEW BGP speaker that
receives the AS4_PATH and AS4_AGGREGATOR path attributes in an UPDATE
message from a NEW BGP speaker SHOULD discard these path attributes
and continue processing the UPDATE message.
4.2. Interaction Between NEW and OLD BGP Speakers
4.2.1. BGP Peering
Note that peering between a NEW BGP speaker and an OLD one is
possible only if the NEW BGP speaker has a 2-octet AS number.
However, this document does not assume that an Autonomous System with
NEW speakers has to have a globally unique 2-octet AS number --
AS_TRANS could be used instead (even if a multiple Autonomous System
would use it).
...
Из настроек Циски:
hostname (config)#router bgp ?
<1-4294967295> Autonomous system number
<1.0-XX.YY> Autonomous system number
Про записи второго asdot вида рассказывают тут: http://tools.ietf.org/html/rfc5396
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