Field Notice: FN - 63866 - Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers TCAM Exhaustion - Configuration Change Recommended

Notice

THIS FIELD NOTICE IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTY OF MERCHANTABILITY. YOUR USE OF THE INFORMATION ON THE FIELD NOTICE OR MATERIALS LINKED FROM THE FIELD NOTICE IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS FIELD NOTICE AT ANY TIME.

Revision History

Revision	Publish Date	Comments
1.0	18-Aug-14	Initial Release
10.0	11-Oct-17	Migration to new field notice system

Products Affected

Affected Product ID	Comments
RSP720-3CXL-GE
VS-S720-10G-3CXL
WS-F6700-DFC3CXL
WS-SUP720-3BXL
WS-SUP720-3BXL=

Defect Information

Defect ID	Headline
CSCvf34445	Dummy defect for field notices that were created with out defects

Problem Description

On August 8, 2014, the Classless Inter-Domain Routing (CIDR) Report, which provides statistics on the global Internet routing table, reported that the global Internet routing table had passed 512,000 routes for the first time in Internet history. When the total number of IPv4 routes exceeds 512,000 on a Cisco Catalyst 6500 Series switch or Cisco 7600 Series routers that run Supervisor 720 (Sup720) engines, the hardware Ternary Content Addressable Memory (TCAM) might report an exception that results in network instability.

 

Background

All of the Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers with Sup720 engines that operate in 3BXL or 3CXL mode are configured in order to program only 512,000 IPv4 routes in the hardware TCAM by default.

Problem Symptom

On the Catalyst 6500 and Cisco 7600 Series platforms, all of the IPv4/IPv6/MPLS routing information is stored in special high-speed memory called Forwarding Information Base (FIB) TCAM.

When a route is programmed into the Cisco Express Forwarding (CEF) table in the main memory (DRAM), a copy of that route is stored in the hardware FIB TCAM on the Supervisor Policy Feature Card (PFC), as well as any Distributed Forwarding Card (DFC) on the modules.

By default, these platforms are configured as shown here: 

IPv4 + MPLS - 512k (default) 

IPv6 + IP Multicast - 256k (default)

When the number of IPv4 + MPLS routes exceed 512,000, the system experiences TCAM exception and might report:

%MLSCEF-DFC4-7-FIB_EXCEPTION: FIB TCAM exception, Some entries will be  
 software switched   
%MLSCEF-SP-7-FIB_EXCEPTION: FIB TCAM exception, Some entries will be  
 software switched

It is important to be aware that the aforementioned errors are reported only once when the TCAM limit is exceeded. Even if the total number of routes withdraw below the configured limit, the switch remains in the exception state until it is cleared:

Catalyst6509#show mls cef exception status 
Current IPv4 FIB exception state = TRUE
Current IPv6 FIB exception state = FALSE
Current MPLS FIB exception state = FALSE

As a result of this TCAM exception condition, connectivity is affected, which might result in elevated CPU usage due to the software switching.

 

Workaround/Solution

Refer to the CAT 6500 and 7600 Series Routers and Switches TCAM Allocation Adjustment Procedures document on Cisco.com for more details about this issue and the associated workaround/solution.

 

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:

• Open a service request on Cisco.com
• By email
• By telephone

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