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Chabot College. ELEC 99.08 autoinstall and SLARP. Autoinstall. Scenario: We plug in and connect a brand-new router. Wouldn’t it be great if it could load its configuration file automatically?

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chabot college
Chabot College

ELEC 99.08

autoinstall and SLARP

autoinstall
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?
autoinstall1
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 12.0.4 or older.
autoinstall2
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”

192.168.0.2

192.168.0.1

slarp1
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

Serial0 3.0.0.1 YES SLARP up up

Serial1 unassigned YES unset administratively down down

Address resolved via SLARP

slarp2
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

Serial0 3.0.0.1 YES SLARP up up

Serial1 unassigned YES unset administratively down down

Other interfaces shut down

slarp3
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

Serial0 3.0.0.1 YES SLARP up up

Serial1 unassigned YES unset administratively down down

Other interfaces shut down

slarp4
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.

autoinstall3
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

!

autoinstall4
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

192.168.0.2

192.168.0.1

“Is there a tftp

server that can send

me a config file?”

autoinstall5
Autoinstall
  • When no tftp server answers these broadcasts, delays and error messages result:

%Error opening tftp://255.255.255.255/network-confg (timeout)%Error opening tftp://255.255.255.255/cisconet.cfg (timeout)%Error opening tftp://255.255.255.255/router-confg (timeout)%Error opening tftp://255.255.255.255/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.
disabling autoinstall
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

!

to prevent autoinstall from running
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...
in our lab
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!