If AR router support 4-byte ASN ?
1,ARx9 series router support 4-byte ASN;ARx8 series router does not support 4-byte ASN. (ASN:Autonomous System Number )
2,if router can not support 4-byte ASN,we can use "peer X.X.X.X as 23456" to work with a BGP speaker support the 4-octet AS numbers.
The AS number 23456 has been assigned by the IANA for AS_TRANS. You can know more detail from RFC 4893--BGP Support for Four-octet AS Number Space.