IP Addressing: Fragmentation and Reassembly Configuration Guide, Cisco IOS XE Release 3S
GRE Fragment and Reassembly Performance Tuning
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GRE Fragment and Reassembly Performance Tuning

GRE Fragment and Reassembly Performance Tuning

Last Updated: November 26, 2012

The GRE Fragment and Reassembly Performance Tuning feature enables you to customize reassembly resources. Reassembly resources are equally allocated to each interface to prevent fragment-related attack. However, in some generic routing encapsulation (GRE) tunnel deployments, fragments are reassembled in specific interfaces. This feature also allows you to adjust the reassembly timer to free up incomplete fragment sessions quickly and reserve the reassembly resources for high priority packets.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Restrictions for GRE Fragment and Reassembly

  • The IPv4 or IPv6 protocol must be enabled on an interface.
  • This feature supports manually created tunnel interfaces or physical interfaces (virtual template is not officially supported).

Information About GRE Fragment and Reassembly

Fragmentation and Reassembly

In Cisco software, packets may be dropped due to nonavailability of reassembly resources of an interface when fragments arrive concurrently on an interface, though, other interfaces have the resources to reassemble fragments. In some cases, some interfaces need additional resources, such as generic routing encapsulation (GRE) tunnel deployment, and resources are freed only when fragments are reassembled. Therefore, if all fragments are not received, the reassembly resources are not freed.

The GRE Fragment and Reassembly Performance Tuning feature improves reassembly performance by reassembling high priority fragments first so that these fragments are not dropped when low priority fragments occupy the reassembly resources.

How to Use GRE Fragment and Reassembly

Configuring GRE Fragment and Reassembly (GFR)

Perform this task to do the following:

  • Enable generic routing encapsulation (GRE) Fragment and Reassembly (GFR) on an interface
  • Specify maximum threshold values to combat buffer overflow and control memory usage
  • Verify GFR configurations
SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.   Enter one of the following:

  • ip reassembly [max-reassemblies number] [timeout milliseconds] [percentage percent {dscp dscp-value | precedence precedence-value}]
  • ipv6 reassembly [max-reassemblies number] [timeout milliseconds] [percentage percent {dscp dscp-value | precedence precedence-value}]

5.    end

6.   Enter one of the following:

  • show ip reassembly interface type number
  • show ipv6 reassembly interface type number


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
interface type number


Example:

Device(config)# interface GigabitEthernet 0/0/0

 

Configures an interface type and enters interface configuration mode.

 
Step 4
Enter one of the following:
  • ip reassembly [max-reassemblies number] [timeout milliseconds] [percentage percent {dscp dscp-value | precedence precedence-value}]
  • ipv6 reassembly [max-reassemblies number] [timeout milliseconds] [percentage percent {dscp dscp-value | precedence precedence-value}]


Example:

Device(config-if)# ip reassembly max-reassemblies 1024 timeout 1000 percentage 50 precedence critical routine



Example:

Device(config-if)# ipv6 reassembly max-reassemblies 1024 timeout 1000 percentage 50 precedence critical routine

 

Enables GFR on an IPv4 or IPv6 interface, as appropriate.

 
Step 5
end


Example:

Device(config-if)# end

 

Exits interface configuration mode and returns to privileged EXEC mode.

 
Step 6
Enter one of the following:
  • show ip reassembly interface type number
  • show ipv6 reassembly interface type number


Example:

Device# show ip reassembly GigabitEthernet 0/0/0



Example:

Device# show ipv6 reassembly GigabitEthernet 0/0/0

 

Displays statistical information of the GFR configured about the interface.

 

Configuration Examples for GRE Fragment and Reassembly

Example: Configuring GFR

The following example shows how to configure GFR on a Gigabit Ethernet interface and specify the maximum reassembly and timeout settings:

interface GigabitEthernet 0/0/0
 ip address 10.10.10.1 255.255.255.0
 ipv6 address 2001:DB8:1::1
 ip reassembly max-reassemblies 1024 timeout 1 percentage 50 dscp ef
 ipv6 reassembly max-reassemblies 1024 timeout 1 percentage 50 dscp ef 
 ip virtual-reassembly max-reassemblies 1024 timeout 1 percentage 10 dscp af41 
 ipv6 reassembly out max-reassemblies 1024 timeout 1 percentage 50 precedence cs1

Additional References for GRE Fragment and Reassembly

Technical Assistance

Description Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for GRE Fragment and Reassembly

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1 Feature Information for GRE Fragment and Reassembly
Feature Name Releases Feature Information

GRE Fragment and Reassembly Performance Tuning

Cisco IOS XE Release 3.8S

The GRE Fragment and Reassembly Performance Tuning feature enables you to customize reassembly resources. Reassembly resources are equally allocated to each interface to prevent fragment-related attack. However, in some generic routing encapsulation (GRE) tunnel deployments, fragments are reassembled in specific interfaces. This feature also allows you to adjust the reassembly timer to free up incomplete fragment sessions quickly and reserve the reassembly resources for high priority packets.

The following commands were introduced or modified: ip reassembly, show ip reassembly.

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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