---
title: client.as.number
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/variables/client-connection/client-as-number
---

**Type:** INTEGER  
**Access:** read-only

**Available in:** all subroutines

[Autonomous system](https://en.wikipedia.org/wiki/Autonomous_system_(Internet)) (AS) number.

The `INTEGER` type in VCL is [wide enough](https://www.fastly.com/documentation/reference/vcl/types/integer/)
to support the full range of 32-bit AS numbers.

## Converting to asdot+ format

Formatting these numbers to base 10 (e.g., by implicit conversion to a `STRING` type)
will give an `asplain` representation of the number, which is just its base 10
representation.

[RFC 5396](https://tools.ietf.org/html/rfc5396) introduces the `asdot+` format,
which represents a 32-bit AS number as two 16-bit parts.
The following VCL illustrates constructing an `asdot+` formatted number:

```vcl
sub client_asn_dotplus STRING {
  declare local var.hi INTEGER;
  declare local var.lo INTEGER;
  declare local var.s STRING;

  set var.hi = client.as.number;
  set var.hi >>= 16;
  set var.lo = client.as.number;
  set var.lo &= 0xFFFF;

  set var.s = client.as.number ": " var.hi "." var.lo;

  return var.s;
}
```

## Examples

The 32-bit AS number 65550 (reserved by
[RFC 5398](https://tools.ietf.org/html/rfc5398) for documentation use)
is rendered as `1.14`.

Several ranges of AS numbers are reserved for various purposes. The following
VCL fragment illustrates categorizing AS numbers into these ranges:

```vcl
sub client_asn_category STRING {
  declare local var.asn_category STRING;

  if (client.as.number < 0 || client.as.number > 0xFFFFFFFF) {
    set var.asn_category = "invalid";
  } else if (client.as.number == 0) {
    set var.asn_category = "reserved"; # RFC 1930
  } else if (client.as.number <= 23455) {
    set var.asn_category = "public";
  } else if (client.as.number == 23456) {
    set var.asn_category = "transition"; # RFC 6793
  } else if (client.as.number <= 64534) {
    set var.asn_category = "public";
  } else if (client.as.number <= 64495) {
    set var.asn_category = "reserved";
  } else if (client.as.number <= 64511) {
    set var.asn_category = "documentation"; # RFC 5398
  } else if (client.as.number <= 65534) {
    set var.asn_category = "private";
  } else if (client.as.number == 65535) {
    set var.asn_category = "reserved";
  } else if (client.as.number <= 65551) {
    set var.asn_category = "documentation"; # RFC 4893, RFC 5398
  } else if (client.as.number <= 131071) {
    set var.asn_category = "reserved";
  } else if (client.as.number <= 4199999999) {
    set var.asn_category = "public";
  } else if (client.as.number <= 4294967294) {
    set var.asn_category = "private"; # RFC 6996
  } else if (client.as.number == 4294967295) {
    set var.asn_category = "reserved";
  } else {
    set var.asn_category = "unknown";
  }

  return var.asn_category;
}
```