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This chapter documents commands used to configure switching and NetFlow in Cisco IOS software. For guidelines on configuring switching and NetFlow, refer to the Cisco IOS Switching Services Configuration Guide.
Note In Cisco IOS Release 11.3, all commands supported on the Cisco 7500 series routers are also supported on Cisco 7000 series routers.
To clear the NetFlow statistics, use the clear ip flow stats EXEC command.
This command has no arguments or keywords.
This command first appeared in Cisco IOS Release 11.1 CA.
The show ip cache flow command displays the NetFlow statistics. Use the clear ip flow command to clear the NetFlow statistics.
The following example clears the NetFlow statistics on the router:
You can use the master indexes or search online to find documentation of related commands.
Use the encapsulation isl subinterface configuration command to enable the Inter-Switch Link (ISL). ISL is a Cisco protocol for interconnecting multiple switches and routers, and for defining VLAN topologies.
This command first appeared in Cisco IOS Release 11.1.
ISL encapsulation is configurable on Fast Ethernet interfaces.
ISL encapsulation adds a 26-byte header to the beginning of the Ethernet frame. The header contains a 10-bit VLAN identifier that conveys VLAN membership identities between switches.
The following example enables ISL on Fast Ethernet subinterface 2/1.20:
You can use the master indexes or search online to find documentation of related commands.
bridge-group
debug vlan
show bridge vlan
show interfaces
show vlans
Use the encapsulation sde subinterface configuration command to enable IEEE 802.10 encapsulation of traffic on a specified subinterface in virtual LANs. IEEE 802.10 is a standard protocol for interconnecting multiple switches and routers, and for defining VLAN topologies.
This command first appeared in Cisco IOS Release 10.3.
SDE encapsulation is configurable only on the following interface types:
The following example enables SDE on FDDI subinterface 2/0.1 and assigns a VLAN identifier of 9999:
You can use the master indexes or search online to find documentation of related commands.
bridge-group
debug vlans
show bridge vlan
show interfaces
show vlans
To control the invalidation rate of the IP route cache, use the ip cache-invalidate-delay global configuration command. To allow the IP route cache to be immediately invalidated, use the no form of this command.
minimum = 2 seconds
maximum = 5 seconds, and 3 seconds with no more than zero invalidation requests
This command first appeared in Cisco IOS Release 10.0.
All cache invalidation requests are honored immediately.
This command should typically not be used except under the guidance of technical support personnel. Incorrect settings can seriously degrade network performance.
The IP fast-switching and autonomous-switching features maintain a cache of IP routes for rapid access. When a packet is to be forwarded and the corresponding route is not present in the cache, the packet is process-switched and a new cache entry is built. However, when routing table changes occur (such as when a link or an interface goes down), the route cache must be flushed so that it can be rebuilt with up-to-date routing information.
This command controls how the route cache is flushed. The intent is to delay invalidation of the cache until after routing has settled down. Because route table changes tend to be clustered in a short period of time, and the cache may be flushed repeatedly, a high CPU load might be placed on the router.
When this feature is enabled, and the system requests that the route cache be flushed, the request is held for at least minimum seconds. Then the system determines whether the cache has been "quiet" (that is, less than threshold invalidation requests in the last quiet seconds). If the cache has been quiet, the cache is then flushed. If the cache does not become quiet within maximum seconds after the first request, it is flushed unconditionally.
Manipulation of these parameters trades off CPU utilization versus route convergence time. Timing of the routing protocols is not affected, but removal of stale cache entries is affected.
The following example sets a minimum delay of 5 seconds, a maximum delay of 30 seconds, and a quiet threshold of no more than 5 invalidation requests in the previous 10 seconds:
You can use the master indexes or search online to find documentation of related commands.
Use the ip flow-cache entries global configuration command to change the number of entries maintained in the NetFlow cache. Use the no form of this command to return to the default number of entries.
This command first appeared in Cisco IOS Release 11.1 CA.
Normally the default size of the NetFlow cache will meet your needs. However, you can increase or decrease the number of entries maintained in the cache to meet the needs of your flow traffic rates. For environments with a high amount of flow traffic (such as an internet core router), a larger value such as 131072 (128K) is recommended. To obtain information on your flow traffic, use the show ip cache flow command.
The default is 64K flow cache entries. Each cache entry is approximately 64 bytes of storage. Assuming a cache with the default number of entries, approximately 4MB of DRAM would be required. Each time a new flow is taken from the free flow queue, the number of free flows is checked. If there are only a few free flows remaining, NetFlow attempts to age 30 flows using an accelerated timeout. If there is only one free flow remaining, NetFlow automatically ages 30 flows regardless of their age. The intent is to ensure free flow entries are always available.
 | Caution Cisco recommends that you do not change the NetFlow cache entries. Improper use of this feature could cause network problems. To return to the default NetFlow cache entries, use the no ip flow-cache entries global configuration command. |
The following example increases the number of entries in the NetFlow cache to 131072 (128K):
You can use the master indexes or search online to find documentation of related commands.
To enable the exporting of information in NetFlow cache entries, use the ip flow-export global configuration command. To disable the exporting of information, use the no form of this command.
This command first appeared in Cisco IOS Release 11.1.
This command was modified to include the version keyword in Cisco IOS Release 11.1 CA.
There is a lot of information in a NetFlow cache entry. When NetFlow is enabled with the ip route-cache flow command, you can use the ip flow-export command to configure the router to export the flow cache entry to a workstation when a flow expires. This feature can be useful for purposes of statistics, billing, and security.
Version 5 format includes the source and destination AS addresses, source and destination prefix masks, and a sequence number. Because this change may appear on your router as a maintenance release, support for version 1 format is maintained with the version 1 keyword.
For more information on version 1 and version 5 data format, refer to the "NetFlow Data Format" section in "Configuring NetFlow" chapter of the Cisco IOS Switching Services Configuration Guide.
The following example configures the router to export the NetFlow cache entry to UDP port 125 on the workstation at 134.22.23.7 when the flow expires using version 1 format:
The following example configures the router to export the NetFlow cache entry to UDP port 2048 on the workstation at 134.22.23.7 when the flow expires using version 5 format and including the peer AS information:
You can use the master indexes or search online to find documentation of related commands.
Use the ip route-cache interface configuration command to control the use of high-speed switching caches for IP routing. To disable any of these switching modes, use the no form of this command.
IP autonomous switching is disabled.
Fast switching varies by interface and media.
Optimum switching is enabled on supported interfaces.
Distributed switching is disabled.
This command first appeared in Cisco IOS Release 10.0. The optimum keyword first appeared in Cisco IOS Release 11.1. The distributed keyword first appeared in Cisco IOS Release 11.2.
Using the route cache is often called fast switching. The route cache allows outgoing packets to be load-balanced on a per-destination basis.
The ip route-cache command with no additional keywords enables fast switching and disables.
Cisco routers generally offer better packet transfer performance when fast switching is enabled, with one exception. On networks using slow serial links (64K and below), disabling fast switching to enable the per-packet load sharing is usually the best choice.
You can enable IP fast switching when the input and output interfaces are the same interface, using the ip route-cache same-interface command. This normally is not recommended, though it is useful when you have partially meshed media, such as Frame Relay. You could use this feature on other interfaces, although it is not recommended because it would interfere with redirection.
On Cisco 7500 series routers with RSP and Versatile Interface Processor (VIP) controllers, the VIP hardware can be configured to switch packets received by the VIP with no per-packet intervention on the part of the RSP. When VIP distributed switching is enabled, the input VIP interface tries to switch IP packets instead of forwarding them to the RSP for switching. Distributed switching helps decrease the demand on the RSP.
Not all switching methods are available on all platforms. Refer to the Cisco Product Catalog for information about features available on the platform you are using.
The following example enables both fast switching and autonomous switching:
The following example disables both fast switching and autonomous switching:
The following example turns off autonomous switching only:
The following example enables VIP distributed NetFlow on the interface:
The following example returns the system to its defaults (fast switching enabled; autonomous switching disabled):
You can use the master indexes or search online to find documentation of related commands.
ip cache-invalidate-delay
show ip cache
To enable NetFlow for IP routing, use the ip route-cache flow interface configuration command. To disable NetFlow, use the no form of this command.
This command has no arguments or keywords.
This command first appeared in Cisco IOS Release 11.1.
NetFlow captures a rich set of traffic statistics. These traffic statistics include user, protocol, port, and type of service information that can be used for a wide variety of purposes such as network analysis and planning, accounting, and billing. To export NetFlow data, use the ip flow-export global configuration command.
NetFlow is supported on IP and IP encapsulated traffic over all interface types and encapsulations except for ISL/VLAN, ATM and Frame Relay interfaces when more than one input access control list is used on the interface, and ATM LANE.
A network flow is identified as a unidirectional stream of packets between a source and destination—both defined by a network-layer IP address and transport-layer port number. Specifically, a flow is identified as the combination of the following fields:
NetFlow operates by creating a flow cache. The cache includes entries for traffic statistics. Flow information is maintained within the NetFlow cache for all active flows. With NetFlow you can export data (traffic statistics) to a remote workstation for further processing.
NetFlow does not involve any connection-setup protocol either between routers or to any other networking device or end station and does not require any change externally—either to the traffic or packets themselves or to any other networking device. Thus, NetFlow is completely transparent to the existing network, including end stations and application software and network devices like LAN switches. Also, because NetFlow is performed independently on each internetworking device, it does not need to be operational on each router in the network. Network planners can selectively invoke NetFlow (and NetFlow data export) on a router/interface basis to gain traffic performance, control, or accounting benefits in specific network locations.
Note NetFlow does consume additional memory and CPU resources; therefore, it is important to understand the resources required on your router before enabling NetFlow.
The following example enables NetFlow on the interface:
The following example returns the interface to its defaults (fast switching enabled; autonomous switching disabled):
You can use the master indexes or search online to find documentation of related commands.
To display the routing table cache used to fast switch IP traffic, use the show ip cache EXEC command.
This command first appeared in Cisco IOS Release 10.0. The arguments prefix, mask, type, and number first appeared in Cisco IOS Release 10.0. The show ip cache display shows MAC headers up to 92 bytes.
The following is sample output from the show ip cache command:
Table 1 describes significant fields shown in the display.
Show IP Cache Field Descriptions
The following is sample output from the show ip cache command with a prefix and mask specified:
The following is sample output from the show ip cache command with an interface specified:
To display a summary of the NetFlow statistics, use the show ip cache flow EXEC command.
This command has no arguments or keywords.
This command first appeared in Cisco IOS Release 11.1.
This command was modified to update the display with the latest information in Cisco IOS Release 11.1 CA.
The following is a sample output from the show ip cache flow command.
Table 2 describes the fields in the packet size distribution lines of the output.
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Packet Size Distribution Field Descriptions
Table 3 describes the fields in the flow switching cache lines of the output.
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Flow Switching Cache Display Field Descriptions
Table 4 describes the fields in the activity-by-protocol lines of the output.
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Activity-By-Protocol Display Field Descriptions
Table 5 describes the fields in the current flow lines of the output.
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Current Flow Display Field Descriptions
You can use the master indexes or search online to find documentation of related commands.
ip route-cache
clear ip flow stats
Posted: Tue Jan 6 16:28:54 PST 2004
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