Upgrading Cisco IOS Software

Cisco IOS is constantly being revised to add new features or to fix bugs in previous versions. The process of upgrading software on a Cisco router can be broken down into three main steps:

1. Back up the current Cisco IOS.

2. Copy the new Cisco IOS to the router.

3. Reload the Cisco router and verify the new IOS.

Backing Up the Current IOS

The first part of backing up the current IOS involves determining what version of IOS is running on the router and the filename of the software image. It is also necessary to note the size available in Flash memory. The new version of IOS must not be larger than the total Flash memory on the router. The show version command displays this information, as shown here:

 NFLD#sh vers Cisco Internetwork Operating System Software IOS (tm) 2500 Software (C2500-J-L), Version 11.2(13), RELEASE SOFTWARE (fc1) Copyright (c) 1986-1998 by cisco Systems, Inc. Compiled Tue 31-Mar-98 10:27 by tlane Image text-base: 0x0303F1E4, data-base: 0x00001000 ROM: System Bootstrap, Version 11.0(10c)XB1, PLATFORM SPECIFIC RELEASE SOFTWARE (fc1) BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R),  Version 11.0(10c)XB1, PLATFORM SPECIFIC RELEASE SOFTWARE (fc1) NFLD uptime is 7 minutes System restarted by reload System image file is "flash:11-2-13.img", booted via flash cisco 2500 (68030) processor (revision L) with 2048K/2048K bytes of memory. Processor board ID 07110268, with hardware revision 00000000 Bridging software. SuperLAT software copyright 1990 by Meridian Technology Corp. X.25 software, Version 2.0, NET2, BFE and GOSIP compliant. TN3270 Emulation software. 2 Ethernet/IEEE 802.3 interface(s) 2 Serial network interface(s) 32K bytes of non-volatile configuration memory. 16384K bytes of processor board System flash (Read ONLY) Configuration register is 0x2102 

From the preceding command listing, we can determine that we have 16,384KB of Flash memory available. Therefore, we can copy any software image less than or equal to 16,384KB to this device. The name of the file is provided as "11-2-13.img." After the memory requirements and the filename have been determined, we need to copy the old image to a TFTP server. This step gives us a fallback procedure in case the new software image is corrupt:

In the following example, the exclamation mark indicates the system is working. In other examples, you will see the letter "e" (erasing) repeated as the system works on a command. The repeated letters simply mean you should be patient and let the system complete the current command before entering another one.

 NFLD#copy flash TFTP System flash directory: File Length  Name/status  1  7969232 11-2-13.img [7969296 bytes used, 8807920 available, 16777216 total] Address or name of remote host [255.255.255.255]? 172.16.24.134 Source file name? 11-2-13.img Destination file name [11-2-13.img]? <Return> Verifying checksum for '11-2-13.img' (file # 1)... OK Copy '11-2-13.img' from Flash to server  as '11-2-13.img'? [yes/no]y !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Upload to server done Flash copy took 00:04:36 [hh:mm:ss] 

Upgrading the IOS

After the current IOS has been backed up to a TFTP server and the available memory on the router has been checked, we can proceed with the upgrade of the IOS. The new IOS must reside on the TFTP server, as shown here:

 NFLD#copy TFTP flash Proceed? [confirm]<Return> System flash directory: File Length  Name/status  1  7969232 11-2-14.img [7969296 bytes used, 8807920 available, 16777216 total] Address or name of remote host [172.16.24.134]?<RETURN> Source file name? 11-2-14.img Destination file name [11-2-14.img]?<RETURN> Accessing file '11-2-14.img' on 172.16.24.134... Loading 11-2-14.img from 172.16.24.134 (via Ethernet1): ! [OK]<RETURN> Erase flash device before writing? [confirm]<RETURN> Flash contains files. Are you sure you want to erase? [confirm]<RETURN> System configuration has been modified. Save? [yes/no]: <RETURN> % Please answer 'yes' or 'no'. Y System configuration has been modified. Save? [yes/no]: y Building configuration... [OK] <RETURN> Copy '11-2-14.img' from server  as '11-2-14.img' into Flash WITH erase? [yes/no]y %SYS-5-RELOAD: Reload requested %SYS-4-CONFIG_NEWER: Configurations from version 11.2 may not be correctly understood. %FLH: 11-2-14.img from 172.16.24.134 to flash ... System flash directory: File Length  Name/status  1  7969232 11-2-14.img [7969296 bytes used, 8807920 available, 16777216 total] Accessing file '11-2-14.img' on 172.16.24.134... Loading 11-2-14.img from 172.16.24.134 (via Ethernet1): ! [OK] Erasing device... eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee   ...erased Loading 11-2-14.img from 172.16.24.134 (via Ethernet1): !!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! [OK - 7969232/16777216 bytes] Verifying checksum... OK (0xF865) Flash copy took 0:07:00 [hh:mm:ss] 

Reloading the Router

Depending on what type of router mode we have, when we copy a new version of software to the router, the router will either reload itself or return with the Router# prompt. If the router returns with a prompt, we use the Router# reload command to restart the router and load the new software. The router reload command is as follows :

 Router# reload