CISCO NETWORKING ACADEMY Chabot College ELEC 99.08 autoinstall and SLARP

CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY

Chabot CollegeChabot College

ELEC 99.08ELEC 99.08autoinstall and SLARP


AutoinstallAutoinstall• 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?


AutoinstallAutoinstall• 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.


AutoinstallAutoinstall• Step 1 - autoinstall obtains an IP address for the connected serial

interface using SLARP - Serial Line Address Resolution Protocol:

new router existing router

HDLC192.168.0.1

“Give me an IP address”

192.168.0.2


SLARPSLARP


SLARPSLARP• 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


SLARPSLARP• Interface summary during setup dialog shows results of

SLARPing:





Other interfaces shut down


SLARPSLARP• E0 and S1 have been shutdown. • In order to bring these interfaces back up, the administrator must manually remove the

shutdown command.





Other interfaces shut down


SLARPSLARP• 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.


AutoinstallAutoinstall• Step 2 - autoinstall writes this line to the default config on the

new router:

version 12.0service timestamps debug uptimeservice timestamps log uptimeno service password-encryptionservice config!hostname Router!


AutoinstallAutoinstall• 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

HDLC192.168.0.1192.168.0.2

“Is there a tftp server that can send

me a config file?”


AutoinstallAutoinstall• 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 AutoinstallDisabling 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 12.0service timestamps debug uptimeservice timestamps log uptimeno service password-encryptionno service config!hostname Router!


To prevent autoinstall from To prevent autoinstall from running...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!

Documents

CISCO NETWORKING ACADEMY Chabot College ELEC 99.08 autoinstall and SLARP