Catalyst 4500 Series Switch SW Configuration Guide, Release IOS-XE 3.2.xSG
Configuring Flexible NetFlow
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Configuring Flexible NetFlow

Table Of Contents

Configuring Flexible NetFlow


Configuring Flexible NetFlow


Flow is defined as a unique set of key fields attributes, which might include fields of packet, packet routing attributes, and input and output interface information. A NetFlow feature defines a flow as a sequence of packets that have the same values for the feature key fields. Flexible Netflow (FNF) allows you to collect and optionally export a flow record that specifies various flow attributes. Netflow collection supports IP, IPv6 and Layer 2 traffic.


Note This chapter provides Catalyst 4500 switch specific information. For more information, refer to the URL:

http://www.cisco.com/en/US/products/ps6965/products_ios_protocol_option_home.html


The following items apply to the Catalyst 4500 series switch:

1. The Catalyst 4500 series switch supports ingress flow statistics collection for switched and routed packets; it does not support Flexible Netflow on egress traffic.

2. Supervisor Engine 7-E supports a 100,000 entry hardware flow table, which is shared across all the ports and VLANs on the switch. To limit the number of table entries on a given interface or VLAN, enter the cache entries number command.

The following example illustrates how to configure the flow monitor m1 cache to hold 1000 entries. With this configuration, interface gig 3/1 can create a maximum of 1000 flows and interface gig 3/2 can create a maximum of 1000 flows:

flow exporter e1
    ! exporter specifies where the flow records are send to
    destination 20.1.20.4 
!
flow record r1
    ! record specifies packet fields to collect
    match ipv4 source address
    match ipv4 destination address
    collect counter bytes long
    collect counter packets long
    collect timestamp sys-uptime first
    collect timestamp sys-uptime last
!
flow monitor m1
    ! monitor refers record configuration and optionally exporter
    ! configuration. It specifies the cache size i.e. how many unique flow
    ! records to collect
    record r1
    exporter e1
    cache timeout active 60
    cache timeout inactive 30
    cache entries 1000 

!interface GigabitEthernet 3/1
    ! layer2-switched allows collection of flow records even when the packet is  
    ! bridged
     ip flow monitor m1 layer2-switched input
!
interface GigabitEthernet 3/2
    ip flow monitor m1 input
!

3. Flow collection is supported on multiple targets (Port, VLAN, per-port per-VLAN (FNF can be enabled on a specific VLAN on a given port)) and on a port-channel (FNF is configured on the port-channel interface, rather than individual member ports).

4. 64 unique flow record configurations are supported.

5. Flow QoS/UBRL and FNF cannot be configured on the same target. (For information on Flow-based QoS, see the section Flow-based QoS.)

6. 14,000 unique IPv6 addresses can be monitored.

7. On a given target, one monitor per traffic type is allowed. However, you can configure multiple monitors on the same target for different traffic types.

For example, the following configuration is allowed:

     ! vlan config 10
           ip flow monitor <name> input
           ipv6 flow monitor <name> input
     !

The following configuration is not allowed:

    !
    interface GigabitEthernet 3/1
           ip flow monitor m1 input
           ip flow monitor m2 input
 
   

8. On a given target monitoring Layer 2 and Layer 3, simultaneous traffic is not supported:

     interface channel-group 1
           datalink flow monitor m1 input
            ip flow monitor m2 input

!

9. Selection of Layer 2 and Layer 3 packet fields in a single flow record definition is not allowed. However, packet COS and Layer 3 packet field selection is allowed.

10. Only permanent and normal flow cache types are supported.

11. Supervisor Engine 7-E does not support predefined records like traditional routers (record neflow ipv4 original-input).

12. Supervisor Engine 7-E does not support flow based sampler.

13. Interface option not supported with Cos,Tos, TTL or Packet length options.

14. The configuration of the flow exporter does not support the option output features.

15. Flow aging in flow cache is controlled through active and in-active timer configuration. The minimum for active and in-active aging timers is 5 seconds. The timers must be in units of 5 seconds.


Note Flows in the hardware table are deleted after 5 seconds of in-activity irrespective of the active or in-active timer configuration values. This allows you to create new hardware flows quickly.


16. First and Last-seen flow timestamp accuracy is within 3 seconds.

17. 2048 Flow monitors and records are supported.

When TTL is configured as a flow field, the following values are reported for a given packet TTL value. Table 33-1 lists the packet TTL and reported values.

Table 33-1 TTL Map: TTL Configured

Packet TT Value
Reported Value

0

0

1

1

2-10

10

11-25

25

26-50

50

51-100

100

100-150

150

150-255

255


When packet length is configured as a flow field, the following values are reported for a given packet length value. Table 33-2 lists the packet length and reported values.

Table 33-2 Packet Length Map: Packet Length Configured

Packet Length
Reported Value

0-64

64

65-128

128

129-256

256

257-512

512

513-756

756

757-1500

1500

1500-4000

4000

4000+

8192


l

The following table lists the options available through FNF and the supported fields.

Table 33-3 Options Available through FNF and the Supported Fields

Field
Description
Comments

Data Link Fields (Layer 2 Flow Label + A94)

dot1q priority

802 1Q user

 

dot1q vid

802.1Q VLAN ID

Only output VLAN as collect option is supported.

mac destination-address

Upstream destination MAC address

 

mac source-address

Down stream source MAC address

 
IPv4 Fields

destination address

IPv4 destination address

Yes

DSCP

IPv4 DSCP (part of TOS)

 

fragmentation flags

IPv4 fragmentation flags

Supported as non key. DF flag is not supported

is-multicast

Indicator of an IPv4 multicast packet (0 - if it's not, 1 - if it is)

Supported as non-key

Precedence

IPv4 precedence

 

Protocol

IPv4 protocol

 

source address

IPv4 source address

 

total length

IPv4 datagram

Values are reported based on Table 33-2.

Total length minimum

Minimum packet size seen

 

Total length maximum

Maximum packet size seen

 

Tos

IPv4 Type of Service (TOS)

 

ttl

Pv4 Time to Live (TTL)

Values are reported based on Table 33-1.

ttl minimum

FNF supports this field only in mon-key mode

 

ttl maximum

FNF supports this field only in mon-key mode

 
IPv6 Fields

destination address

IPv6 destination address

 

dscp

IPv6 DSCP (part of IPv6 traffic class)

 

flow-label

IPv6 flow label

 

is-multicast

Indicator of an IPv6 multicast packet (0 - if it's not, 1 - if it is)

Supported as a non-key field

hop-limit

IPv6 hop limit (replaces IPv4 ttl)

Values are reported based on Table 33-1.

hop-limit minimum

IPv6 minimum hop limit value seen in the flow. It can be used as a non-key field only.

 

hop-limit maximum

IPv6 maximum hop limit value seen in the flow. It can be used as a non-key field only.

 

next-header

IPv5 next header type

Only first next header is reported

total length

IPv6 total packet length

Values are based on Table 33-2.

Total length minimum

Minimum packet size seen

 

Total length maximim

Maximum packet size seen

 

protocol

IPv6 next header type in the last IPv6 extension header

 

source address

IPv6 source address

 

traffic-class

IPv6 traffic class

Yes

Routing Attributes

forwarding-status

Forwarding status for the packet (forwarded, terminated in the router, dropped by ACL, RPF, CAR)

Supported as a non-key field

Layer 4 Header Fields

Field

Description

Comments

TCP Header Fields

destination-port TCP destination number

TCP destination port

 

flags [ack] [fin] [psh] [rst] [syn] [urg]

TCP flags.

Supported as non-key fields.

source-port

TCP source port

 

UDP Header Fields

destination-port

UDP destination port

 

source-port

UDP source port

 

ICMP Header Fields

code

ICMP code

 

type

ICMP type

 

IGMP Header Fields

type

IGMP

 

Interface Fields

input

Input interface index

 

output

Input interface index

Output interface can be supported only as non-key.

Flexible NetFlow feature related fields

direction: input

   

Counter Fields

bytes

32 bit counters

 

bytes long

64 bit counter

 

packets

32 bit counters

 

packets long

64 bit counter of the packets in the flow

 

Timestamp

first seen

Time-stamp of the first packet that is accounted in the flow (in milliseconds, starting from the router boot-up)

3 sec accuracy

last seen

Time-stamp of the last packet that is accounted in the flow (in milliseconds, starting from the router boot-up)

3 sec accuracy


Configuring Flow Monitor Cache Values

Setting active cache timeout to a small value may cause the flows to be exported more frequently to the remote collector. This also causes software to delete flows from the local cache after exporting. So, cache statistics reported by switch may not display the actual flows being monitored.