Chabot College
ELEC 99.08
autoinstall and SLARP
CISCO NETWORKING ACADEMY
Autoinstall
• Scenario: We plug in and connect a brandnew 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?
CISCO NETWORKING ACADEMY
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.
CISCO NETWORKING ACADEMY
Autoinstall
• Step 1 - autoinstall obtains an IP address for
the connected serial interface using SLARP Serial Line Address Resolution Protocol:
new router
“Give me
192.168.0.2
an IP address”
CISCO NETWORKING ACADEMY
existing router
HDLC
192.168.0.1
SLARP
CISCO NETWORKING ACADEMY
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
Ethernet0
unassigned
YES unset
administratively down
Serial0
3.0.0.1
YES SLARP
up
Serial1
unassigned
YES unset
administratively down
Address resolved via SLARP
CISCO NETWORKING ACADEMY
Protocol
down
up
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
Ethernet0
unassigned
YES unset
administratively down
Serial0
3.0.0.1
YES SLARP
up
Serial1
unassigned
YES unset
administratively down
Other interfaces shut down
CISCO NETWORKING ACADEMY
Protocol
down
up
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
Ethernet0
unassigned
YES unset
administratively down
Serial0
3.0.0.1
YES SLARP
up
Serial1
unassigned
YES unset
administratively down
Other interfaces shut down
CISCO NETWORKING ACADEMY
Protocol
down
up
down
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.
CISCO NETWORKING ACADEMY
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
!
CISCO NETWORKING ACADEMY
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
192.168.0.2
“Is there a tftp
server that can send
me a config file?”
CISCO NETWORKING ACADEMY
existing router
HDLC
192.168.0.1
Autoinstall
• When no tftp server answers these broadcasts,
delays and error messages result:
%Error opening
(timeout)
%Error opening
(timeout)
%Error opening
(timeout)
%Error opening
(timeout)
tftp://255.255.255.255/network-confg
tftp://255.255.255.255/cisconet.cfg
tftp://255.255.255.255/router-confg
tftp://255.255.255.255/ciscortr.cfg
• 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.
CISCO NETWORKING ACADEMY
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
!
CISCO NETWORKING ACADEMY
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...
CISCO NETWORKING ACADEMY
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!
CISCO NETWORKING ACADEMY