AutoInstall Product Bulletin

Product Bulletin #213

Plug and Play

AutoInstall makes Cisco's access routers plug and play.

Previous to this feature, customers who purchased any vendor's routers had three choices:

  1. send a network administrator to every installation site;
  2. have all routers shipped to a central lab for configuration;
  3. ask a vendor to pre-configure routers at the factory.
Neither meets the needs of today's customers, who must deploy router networks rapidly and cost-effectively. Sending an administrator to every site is costly and time-consuming; and often there are not enough experts to go around. Pre-configuring routers either at a central lab or at factory is cumbersome, inflexible and error-prone; when the pre-configured routers are shipped out, special care must be taken to ensure that each is sent to the designated location.


By making routers plug and play at the installation site, AutoInstall
  1. minimizes the cost of router installation and
  2. speeds up network deployment in many customer environments.

Since the installation process no longer requires someone with any knowledge of router software configuration, central administrators no longer have to travel to remote sites to get routers up and running. Instead, they can have remote branch personnel physically install the router and interconnect its LAN/WAN cables (and the modem or CSU/DSU). Once the router is switched on, the rest can be automatically controlled from the central site. By installing the router network this way, customers can save travel costs and shorten installation schedules.


For routers with NVRAM, AutoInstall is available with SR 9.1. For routers without NVRAM, AutoInstall has been a feature since SR 8.3.

How It Works

Deploying a remote router usually involves two steps:
  1. physical connections of LAN/WAN interface cables and
  2. router software configuration.

While the former is straightforward, the latter requires more knowledge. AutoInstall significantly simplifies router deployment at remote locations by offloading the software configuration task from the installer. Now the only task required of the remote installer is to physically connect LAN/WAN interface cables and turn on the router. The rest is controlled directly from the central network operations center. Note that while AutoInstall uses primarily IP-based services such as TFTP, DNS etc, it can be used to bring up non-IP remote routers as well. Here are the three steps AutoInstall goes through:

1. Learn IP Address

First, when an access router newrouter is turned ON for the first time, newrouter will send out a SLARP (serial line reverse address resolution protocol) request packet over the HDLC line. Upon receiving the packet, existing will reply with its serial interface IP address. If the address is the first host address of the subnet, for example xx.xx.xx.1 in a Class B network with subnet mask, newrouter will automatically be assigned the second subnet host address to its own serial interface, in this example xx.xx.xx.2.

2. Learn Name

Once newrouter acquires its IP address over the HDLC interface, it will proceed to resolve its name. It does so in two ways. First, a TFTP-request will be broadcasted via the serial line for the global configuration file network-confg. If a reachable TFTP server has been set up with the requested file, newrouter will receive and search through the file and use the hostname associated with its address.

If newrouter cannot find network-confg, or the specified address-name mapping in network-confg, it then broadcasts a reverse domain name server (DNS) request over the network. If the DNS services have been set up, newrouter will resolve its name successfully.

3. Download Full Configuration

Based on the name, newrouter then TFTP-broadcasts for its full configuration file newrouter-confg. If newrouter-confg has been prepared by a central administrator on a TFTP server, it will be automatically downloaded to newrouter's running memory, thereby configuring it for full operation.

If any of the above SLARP, TFTP and reverse DNS request-reply sequence is unsuccessful, the router will be automatically thrown into the setup mode, waiting for console input. Simultaneously, however, it will continue to request for the needed information, with the request frequency dwindling to once every 10 minutes after a few attemps.

Administrative Setup

As described above, AutoInstall initiates a series of protocol communications between newrouter and the existing network. For this plug-and-play process to execute properly, the following conditions and central setup procedures are required before the remote router is turned on. Note that for practical reasons, the central management station can be used as both TFTP and DNS servers.

HDLC and LAN Connections. AutoInstall currently supports HDLC-encapsulated serial connections. In North America this represents ~60-70% of WAN installations; in Europe ~30-40%; in Asia-Pacific ~50-70%. AutoInstall also works for all LAN connections. For IP address resolution in LAN, AutoInstall uses BootP instead of SLARP.

Setting Up network-confg or DNS. For the new router to resolve its name based on the newly discovered IP address, one of the following must be prepared:

Configuring the Existing Router. The existing router on the backbone end of the HDLC line must be configured as follows:

  1. The HDLC-encapsulated serial interface must be assigned an IP address, that is, it cannot be unnumbered. Also, the IP address must be that of the first or second host of the subnet. Any other will cause newrouter to assume that the neighbor is unable to provide it an address via SLARP. For simplicity and consistency, we strongly recommend that xx.xx.xx.1 always be used for the existing router. Note that subnet masks other than 8 bits can be used to conserve use of address space. For example, with a 6-bit Class C subnet mask, the existing router should be assigned cccccccc.cccccccc.cccccccc.ssssss01.

  2. It must be configured with helper addresses that turns TFTP and DNS broadcast traffic into unicast traffic destined for the TFTP/DNS server or management station.

Preparing New Router's Configuration on a TFTP Server For AutoInstall to successfully offload the software configuration task from the remote installer, newrouter's configuration file needs to be prepared by the central administrator as newrouter-confg on a TFTP server before newrouter is powered on. This file can contain the router's full configuration or just what it takes for the administrator to telnet into the router for configuration. If you are deploying many access routers with similar software configurations, it may be possible to speed up the process even more by telneting into an existing access router with like configuration, use the "write network" command to save the configuration to a TFTP server, modify the relevant addresses and names for newrouter and rename the file newrouter-confg.


By making routing plug and play, AutoInstall enables Cisco access routers to be deployed cost effectively. A new router can be drop-shipped directly to a remote installation site, be connected to another Cisco router via a serial line and modem or CSU/DSU, be powered on, and beome fully configured by downloading a centrally administered configuration file.


Some of our competitors have been touting that their routers can be drop-shipped to installation sites directly and be brought on line in a plug-and-play fashion. Cisco's AutoInstall feature is superior to their approaches because it makes plug and play possible for access routing while preserving centralized administrative control.

3Com. 3Com touts that boundary routing eases network administration in remote branches where expertise is scarce. Cisco agrees that ease of management is an important aspect of access internetworking. However, 3Com's bridging approach is at best a subset of what it takes to make internetworking easy to manage. Cisco's AutoInstall is an example that one does not have to give up the benefits of routing to get plug-and-play installation. In fact, Cisco's AutoInstall enables access internetworking devices to be deployed cost effectively while maintaining centralized administrative control.

Proteon. AutoInstall is administratively much simpler, more flexible and less error-prone than Proteon's apporach of "we configure it for you at factory" for the CNX 300. For example, AutoInstall does not require the customer to submit any software configuration information to Cisco as part of the PO. Decoupling configuration requirements from the purchasing process gives customers more flexibility. Also, AutoInstall eliminates the costly possibility of an installation site receiving a router pre-configured for another.

IBM. IBM does not have any comparable remote installation feature.

Wellfleet. Wellfleet does not have any comparable remote installation feature.

Posted: Nov 15 14:39:35 1993
Copyright 1996 © Cisco Systems Inc.