ZTP Workflow Part 3 The HTTP Server

Introduction

In this third blogs, we will go over the details of the HTTP/HTTPS server configuration. You can use any HTTP(S) server as long as they provide the “Content-Length” field in there response to the initial GET request from the client. The ZTP process will reject files of unknown length or file greater than 100MB.

Client Headers

IOS-XR devices include several information as part of the initial HTTP(S) request, a list of theses options are included in the table below. All options are sent in UTF-8

The information provided in the header can be used in place of the DHCP options. It allows the user to simplify the DHCP server configuration and only provide a generic link (e.g.: a PHP script) based on a common option provided by IOS-XR devices (e.g.: option 77/15). The script specific to the device is provided by dissecting the fields in the HTTP header as illlustrated in the following example

Example1 Using the HTTP header with PHP

The following example requires an apache server with PHP installed as a module The script parse the different fields of the headers, extract the Platform ID, the serial number and the operation mode and return a script matching the serial number of the device.

<?php
$headers = apache_request_headers();
foreach ($headers as $header => $value) {
  if (strpos($header, 'cisco-serial') !== false) {
    $serial = str_replace ("UTF-8''", "", $value);
  }
  if (strpos($header, 'cisco-platform') !== false) {
    $platform = str_replace ("UTF-8''", "", $value);
  }
  if (strpos($header, 'cisco-oper') !== false) {
    $operation = str_replace ("UTF-8''", "", $value);
  }
}
if ($operation == "exr-config" && $serial !== "") {
  $file_location = $_SERVER["DOCUMENT_ROOT"] . "/$platform/scripts/$serial.sh";
  if (file_exists($file_location)) {
    header ($_SERVER["SERVER_PROTOCOL"] . " 200 OK");
    header ("Accept-Ranges: bytes");
    header ("Content-Type: application/octet-stream");
    header ("Content-Length:".filesize($file_location));
    readfile ($file_location);
    die ();
  } else {
    die ("Error: File not found.");
  }
} else {
  die ("Error: Device is not in ZTP mode or device serial number not found");
}
?>

The script can be called using a generic DHCP configuration valid for all IOS-XR devices, removing the need of creating host specific sections in the DHCP server.

class "exr-config" {
   match if exists user-class and option user-class = “exr-config”;
}

pool {
     allow member of "exr-config";   
     range 192.168.0.30 192.168.0.254;
     option default-url = "http://192.168.0.22/php/ztp-generic.php";
     }
  }

Server Headers

The HTTP server must include the content length in

Server Configuration

HTTP Server

HTTPs Server

Using RESTConf