Cisco uBR7200 Series Universal Broadband Routers

Field Notice: Adding a 25th Netmask to a Network Database May Cause a Software Forced Crash

May 1, 2002

Products Affected



Cisco IOS® Software

The following Cisco IOS software releases on 7x00, 10000, 12000 and uBR7200 platforms: 12.0(17)S and earlier, 12.1(7)E and earlier.

Problem Description

A router that has acquired routes with 25 different subnet masks (/8.../32) within the same major network (eg.,, ..., may experience memory corruption when installing those routes into the routing table.

This memory corruption triggers a software forced crash on the router.


To determine if you are at risk for this problem, contact the Cisco TAC to help gather the following information

  1. Go into exec mode on the router and enter the command show ip route | i subnets, [0-9][0-9] masks to view the number of different masks within a major network. The number of masks should not exceed 24.

    router#show ip route | i subnets, [0-9][0-9] masks is variably subnetted, 319 subnets, 3 masks is variably subnetted, 36 subnets, 17 masks 
  2. Collect all crash information files from the router that has experienced this problem.

  3. Look for the following error string in the crash files: %SYS-2-CHUNKBADMAGIC: Bad magic number in chunk header. This string indicates memory corruption took place.

To determine if you have hit this bug, perform these steps:

  1. Collect all crash information files from the router. Tthis will be present in bootflash. Use dir bootflash: to view a listing.

  2. Check to see if the following error message is present in the crashinfo file:

    Apr 25 14:06:31.466: %SYS-2-CUNKBADMAGIC: Bad magic number in chunk header, chunk 61B65AB8 data 61B74D2C chunkmagic FF000000 chunk_freemagic FFFFFFFF
    Process= "Check heaps", ipl= 0, pid= 3
    Traceback= 602C25D0 602C27D0 602CA9F8 602BF704 602BF6F0

Problem Symptoms

Cisco IOS software forced a system crash due to memory corruption with the error string %SYS-2-CHUNKBADMAGIC: Bad magic number in chunk header.


To mitigate this problem and protect the network from another occurrence, customers are recommended to filter the /31 address routes with a prefix list to prevent those routes from being added to the routing table. This will limit the number of possible distinct subnet masks to 24.

This protection should be deployed both on external and internal neighbors.

The software fix for Cisco bug ID CSCdt72474 is available in Cisco IOS Software Releases 12.0(17)S1, 12.0(18)S, 12.1(8a)E, 12.1(8), 12.2(2)B, and later.


To follow the bug ID link below and see detailed bug information, you must be a registered user and you must be logged in.




Adding 25th network mask into ndb causes router crash.

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods:

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