Cisco Flexible Netflow Question

Posted on 2014-02-03
Last Modified: 2014-02-21
Hello experts,

I'm in the process of configuring netflow on our Nexus 7K. I have read articles which suggest that I need to add the following command to every single interface

ip flow monitor 'flowname' input

Now we have the following interfaces:

IP Interface Status for VRF "default"(1)
Interface            IP Address      Interface Status
Vlan51         protocol-up/link-up/admin-up      
Vlan53         protocol-up/link-up/admin-up      
Vlan201          protocol-up/link-up/admin-up      
Vlan202          protocol-up/link-up/admin-up      
Vlan203          protocol-up/link-up/admin-up      
Vlan204          protocol-up/link-up/admin-up      
Vlan205          protocol-up/link-up/admin-up      
Vlan206          protocol-up/link-up/admin-up      
Vlan207          protocol-up/link-up/admin-up      
Vlan208          protocol-up/link-up/admin-up      
Vlan209          protocol-up/link-up/admin-up      
Vlan210          protocol-up/link-up/admin-up      
Vlan211          protocol-up/link-up/admin-up      
Vlan212          protocol-up/link-up/admin-up      
Vlan213          protocol-up/link-up/admin-up      
Vlan214          protocol-up/link-up/admin-up      
Vlan215          protocol-up/link-up/admin-up      
Vlan216          protocol-up/link-up/admin-up      
Vlan219          protocol-up/link-up/admin-up      
Vlan220          protocol-up/link-up/admin-up      
Vlan221          protocol-up/link-up/admin-up      
Vlan222          protocol-up/link-up/admin-up      
Vlan223          protocol-up/link-up/admin-up      
Vlan401          protocol-up/link-up/admin-up      
Vlan402          protocol-up/link-up/admin-up      
Vlan403          protocol-up/link-up/admin-up      
Vlan404          protocol-up/link-up/admin-up      
Vlan405          protocol-up/link-up/admin-up      
Vlan501          protocol-up/link-up/admin-up      
Vlan502          protocol-up/link-up/admin-up      
Vlan503          protocol-up/link-up/admin-up      
Vlan601         protocol-up/link-up/admin-up      
Vlan602         protocol-up/link-up/admin-up      
Vlan603         protocol-up/link-up/admin-up      
Vlan604         protocol-up/link-up/admin-up      
Vlan605         protocol-up/link-up/admin-up      
Vlan606         protocol-up/link-up/admin-up      
Vlan607         protocol-up/link-up/admin-up      
Vlan608         protocol-up/link-up/admin-up      
Vlan609         protocol-up/link-up/admin-up      
Vlan610         protocol-up/link-up/admin-up      
Vlan611         protocol-up/link-up/admin-up      
Vlan612         protocol-up/link-up/admin-up      

Should I really be adding the command to every interface here?

Also, when configuring the 'netflow exporter', can someone tell me what is the best practice when selecting the source interface through which NetFlow packets are exported?


Question by:cpatte7372
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LVL 28

Expert Comment

by:Jan Springer
ID: 39829643
for every interface that you want to capture packets, yes.

i use either a loopback interface (preferred) or the interface on the router for the servers.

Author Comment

ID: 39829714

It was suggested, to apply the command on all interfaces with an ip address - whether you wish to capture packets on the interface or not.....!
LVL 28

Expert Comment

by:Jan Springer
ID: 39829747
I put that command on all layer 3 interfaces that I want to capture.  Putting it on your external interfaces and only some of your internal interfaces will result in lop-sided data but it's really all about what you want to see.
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Accepted Solution

cpatte7372 earned 0 total points
ID: 39830365

I know its wrong to monitor both input and output on the same interface, but I can't explain it.

Can you explain why we shouldn't put both input and output on same interface. The same principle as if putting ingress and egress on the same interface...
LVL 28

Expert Comment

by:Jan Springer
ID: 39830879
It's not wrong -- it's just that (at least with Cisco and Brocade), you can only monitor traffic coming into the interfaces.

So, if you want to know all detail with regard to some subset (or all) of your address space, you have to monitor the input of both downstream and upstream to get a clear 2-way traffic pattern picture.

Author Closing Comment

ID: 39876308

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