Troubleshooting TFTP Example
The second-level network engineer
for Orlando has console access to the distribution router named Orlando and IP
connectivity to all other devices in his division. The division supports the
172.21.0.0/16 subnet.
Biff from Network Operations stops by the office.
He reports that somehow the Cisco IOS has been erased from the Orlando router.
He says that he was trying to retrieve it from Baltimore but he cannot get TFTP
to work.
The engineer knows from the base configuration information that
there is at least a 100 MB FastEthernet link between Orlando and Baltimore, so
this would be a good source to use for downloading the IOS image. He connects
to the console port on Orlando to assess the situation.
First, the
available commands from within ROMMON mode are reviewed.
Note that the
ROMMON prompt is on 14 and 15, which indicates that several commands have
already been issued.
Next, he enters the ROMMON boot
command to try to boot the router in case the Cisco IOS image is not really
missing.
Entering
the boot command did not work.
The engineer attempts
to reset the router to see if that will restore the IOS
image.
Entering the
reset command did not restore the image.
He decides
to look for the IOS image in the file system.

Biff is
correct. There is no IOS image in flash memory. At 5858 bytes, base.cfg is not
big enough to be an IOS image. The engineer learns from Biff that the image was
erased while someone was saving a backup configuration file.
It is
decided that TFTP should be used to recover the image. The engineer reviews the
commands available from ROMMON level.

The
engineer decides that tftpdnld is the command necessary to
download the image from Baltimore. Baltimore is running a TFTP server that is
offering an image with the file name
flash:c1700-sv8y-mz.122-8.YL.bin.
He enters the
tftpdnld command.
The attempt
fails and the command output displays messages that are symptoms of an issue
with the TFTP application layer protocol.
The engineer has isolated the
TFTP issues to the tftpdnld ROMMON command needing the IP
address and mask for the local router, the default gateway for the local
router, the IP address of the TFTP server, and the name of the file to be
transferred.
A list of these values is shown below:
Local IP address =
172.21.128.129
Local Mask =
255.255.255.128
Local Default Gateway =
172.21.128.130
TFTP Server =
172.22.128.129
File =
c1700-sv8y-mz.122-8.YL.bin
By reviewing the relevant
information on http://www.cisco.com,
the engineer realizes he needs to enter variable_name=variable to set these
variables.
The engineer configures the TFTP variables on the Orlando router.
This step is
extremely case sensitive. The variables have been configured, after he removes
an extra space.
The engineer now invokes the TFTP program.
After
configuring the parameters to support TFTP, the TFTP download process seems to
work. It appears that the application layer issue of missing TFTP parameters
has been resolved.
The engineer now needs to boot the router using the
new image.

The IOS image has been restored. He finishes the task by
restoring the baseline configuration files.