AS Override和Allowas In之间的区别

1. AS替代：
它的功能允许提供商边缘(PE)路由器在VPN路由和转发访问链路上运行的外部BGP会话上更改客户边缘(CE)设备使用的专用自治系统。专用AS编号更改为PEAS编号。

2.允许进入：
即使路由器在AS-Path中检测到自己的ASN，此功能也允许接收和处理路由。如果路由器将其AS-Path中的ASN视为环路预防机制，则会丢弃BGP网络前缀。

AS Override和Allowas之间的区别在于：

Parameter	AS Override	Allowas In
Overview	It is used by PE to modify AS path. This is done so that prefix is not dropped on default behavior of BGP to disallow its own AS member in AS path of prefix.	It is used as an AS path loop prevention mechanism where default behavior of BGP is to not allow its own AS number in AS Path of prefix.
Output	AS Override feature replaces AS in BGP updates to local AS.	It updates in the BGP that contains local AS is permitted by Allowace In.
Configured at	Its feature is configured at Service Provider End.	Its feature is configured on Customer End.
Configuration	It is configured under: router bgp neighbor as-override	Configured under router bgp neighbor allowas-in
AS Path	There is modification in AS path.	There is no modification in AS path.
Scope.	Configuration performed at Service provider end.	Configuration performed at Service provider end.
Most optimal use.	This approach is best used when customer requires to keep minimum configuration at CE side.	This approach is best used to introduce an exception in BGP as a loop prevention mechanism.