System information

Troubleshooting Hardware and Booting Problems 3-19

Fault-Tolerant Boot Strategies

Although netbooting is useful, network or server failures can make netbooting impossible. After you

have installed and conﬁgured the router’s Flash memory, conﬁgure the boot sequence for the router

to reduce the impact of a server or network failure. The following order is recommended:

1 Boot an image from Flash memory.

2 Boot an image using a netboot.

3 Boot from a ROM image.

Following is an example of how to conﬁgure a router with a fault-tolerant boot sequence.

goriot# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

goriot(config)# boot system flash gsxx

goriot(config)# boot system gsxx 131.108.1.101

goriot(config)# boot system rom

goriot(config)# ^Z

goriot#

%SYS-5-CONFIG_I: Configured from console by console

goriot# copy running-config startup-config

[ok]

goriot#

Using this strategy, a router has three sources from which to boot: Flash memory, netboot, and ROM.

Providing alternative sources can help to mitigate any failure of the TFTP server or the network.

Note The conﬁguration register must be set to allow ROM image booting after failed netbooting

attempts. For more information, refer to the hardware conﬁguration manual for your platform.

Timeouts and Out-of-Order Packets

When netbooting, a client might need to retransmit requests before receiving a response to an ARP

request. These retransmissions can result in timeouts and out-of-order packets.

Timeouts (shown as periods in a netbooting display) and out-of-order packets (shown as

uppercase Os) do not necessarily prevent a successful netboot. It is acceptable to have either or both

timeouts or out-of-order packets occur during the netboot process.

The following examples show console output from netbooting sessions that were successful even

though timeouts and out-of-order packets occurred (exclamation points represent successfully

received packets):

Booting gs3-bfx from 131.108.1.123: !.!!!!!!!!!!!!!!!!!!!!!!

Booting gs3-bfx from 131.108.1.123: !O.O!!!!!!!!!!!!!!!!!!!!!!

If a netboot generates excessive out-of-order packets and timeouts, problems might result. These

problems are discussed later in this chapter, in the section “Booting: Timeouts and Out-of-Order

Packets Prevent Netbooting.”

Information for Technical Support

If you cannot resolve your booting problem using the procedures outlined in this chapter, collect the

following information for your technical support representative:

• ROM images. (Use the show version exec command.)