ASN Conversion
Convert a BGP 4-byte autonomous system number between asplain, asdot, and asdot+ notation. Type a number in any format and the other forms appear instantly. Everything runs in your browser, nothing is sent to any server.
Notation Formats
RFC 5396 defines how 4-byte AS numbers are written. The same AS number can appear in three textual forms.
| Format | Rule | AS 65001 | AS 65546 |
|---|---|---|---|
| asplain | Plain decimal value | 65001 |
65546 |
| asdot+ | Always high.low, where the value equals high × 65536 + low |
0.65001 |
1.10 |
| asdot | asplain when the value fits in 2 bytes (below 65536), asdot+ otherwise | 65001 |
1.10 |
Different vendors default to different formats. Cisco IOS and IOS XE display asplain by default but can be switched to asdot with bgp asnotation dot, while regular expressions in AS path filters must match whichever notation the router is configured to display. Converting between the formats therefore matters when the same AS number appears in configurations from different platforms.
Special Ranges
The converter flags AS numbers that fall in a reserved, private, or documentation range.
| Range (asplain) | Purpose | Reference |
|---|---|---|
| 0 | Reserved, must not be originated | RFC 7607 |
| 23456 | AS_TRANS, placeholder used when a 4-byte ASN crosses a 2-byte-only BGP speaker | RFC 6793 |
| 64496 to 64511 | Documentation and sample code | RFC 5398 |
| 64512 to 65534 | Private use (2-byte) | RFC 6996 |
| 65535 | Reserved (last 2-byte value) | RFC 7300 |
| 65536 to 65551 | Documentation and sample code | RFC 5398 |
| 4200000000 to 4294967294 | Private use (4-byte) | RFC 6996 |
| 4294967295 | Reserved (last 4-byte value) | RFC 7300 |
Everything outside these ranges is publicly assignable through the regional Internet registries.