1. Chabot College
ELEC 99.08
autoinstall and SLARP

2. Autoinstall
Scenario: We plug in and connect a brand-new router. Wouldn’t it be great if it could load its configuration file automatically?
What would the router need to load its config file over the network from a server that holds that file?

3. Autoinstall
Automated process that attempts to find a router configuation file
Autoinstall starts automatically if
A serial interface on a new cisco router with no config is connected via an HDLC-encapusulated serial link to another Cisco router.
the other router is “up”
the router is running an IOS release of or older.

4. Autoinstall
Step 1 - autoinstall obtains an IP address for the connected serial interface using SLARP - Serial Line Address Resolution Protocol:
new router
existing router
HDLC
“Give me an IP address”

5. SLARP

6. Address resolved via SLARP
Interface summary during setup dialog shows results of SLARPing:
First, would you like to see the current interface summary? [yes]:
Interface IP-Address OK? Method Status Protocol
Ethernet0 unassigned YES unset administratively down down
Serial YES SLARP up up
Serial1 unassigned YES unset administratively down down
Address resolved via SLARP

7. Other interfaces shut down
SLARP
Interface summary during setup dialog shows results of SLARPing:
First, would you like to see the current interface summary? [yes]:
Interface IP-Address OK? Method Status Protocol
Ethernet0 unassigned YES unset administratively down down
Serial YES SLARP up up
Serial1 unassigned YES unset administratively down down
Other interfaces shut down

8. Other interfaces shut down
SLARP
E0 and S1 have been shutdown.
In order to bring these interfaces back up, the administrator must manually remove the shutdown command.
First, would you like to see the current interface summary? [yes]:
Interface IP-Address OK? Method Status Protocol
Ethernet0 unassigned YES unset administratively down down
Serial YES SLARP up up
Serial1 unassigned YES unset administratively down down
Other interfaces shut down

9. SLARP SLARP message during boot of router with no config:
Notice: NVRAM invalid, possibly due to write erase.
SLARP: interface Serial0 resolved. This interface has been automatically resolved thru the SLARP process. The router will now attempt to retrieve its name and configuration file.

10. Autoinstall
Step 2 - autoinstall writes this line to the default config on the new router:
version 12.0
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
service config !
hostname Router

11. Autoinstall
Step 3 - “service config” begins a series of broadcasts to request that a tftp server load a configuration file to the new router:
new router
existing router
HDLC
“Is there a tftp
server that can send
me a config file?”

12. Autoinstall
When no tftp server answers these broadcasts, delays and error messages result:
%Error opening tftp:// /network-confg (timeout) %Error opening tftp:// /cisconet.cfg (timeout) %Error opening tftp:// /router-confg (timeout) %Error opening tftp:// /ciscortr.cfg (timeout)
Above, a router that has “SLARPed” is looking on the network for a generic configuration file. Use CTRL-SHIFT-6 and then X to stop this process.

13. Disabling Autoinstall
If your router continues to waste resources looking for a configuration file on the network, you can disable the autoinstall function with this command in config mode:
version 12.0
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
no service config !
hostname Router

14. To prevent autoinstall from running...
Don’t connect a V.35 cable to S0 until you’ve configured the router, or
Turn off the router on the other end of the serial link.
We don’t face this issue in our lab...

15. In Our Lab...
In IOS version 12.0(10), autoinstall does not start automatically when your serial lines are connected.
The IOS does not add the service config command to the default configuration, and does not begin the search for a tftp server. -That’s good!
However the IOS does SLARP and obtain an IP address for one of your serial ports. - That’s not a problem, if you remember it!