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With or without ip route cache-flow in a FastEthernet interface ?

Unanswered Question
Nov 19th, 2002
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I have a 3640 that have 3 channelized E1 interfaces and one fast ethernet interface.

My problem is that I do not have CPU do do alll this job. My CPU average is 85~98% during work hours.

The router have ip cache-flow enabled on all interfaces but not in FastEthernet

my question is:

its better or worst for the CPU cache-flow enabled in fast-ethernet interface?

I dont do nothing yet because is a production router and I dont want to discover

that I was wrong in the real life.


Tanks for all


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DALE FRANCIS Wed, 11/20/2002 - 01:34
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Did you explicitly configure this, if so are you exporting the flows.?? If you are not doing this then i would suggest making sure CEF is enabled by just issueing a sh ip cef command, if it is not enabled it will tell you.


CEF is a great switching mechanism and should reduce CPU burden as FIB and adjacency tables are built based on routing and ARP info so.


If you also do a sh ip proc | exc 0.00 it will indicate which processis taking up CPU also look at your buffers and see how many misses there are etc. It sounds as tho your router is busy processing switching which is a huge burden on CPU resources for a high throughput router.


The command which is hidden "sh interface switching" will indicate whether traffic is being fast switched or processes switched.



bs0000554 Wed, 11/20/2002 - 03:50
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Yes, we are exporting the flows.I cant use CEF.

We are buying a new 3745 350Mhz to make better this work

but we have to wait few months.

One more question about "sh int switching " command

How can I now is the traffic is fast or processes switches?

(see example below)

And as I was write, I want to know if is best or worst have ip route-cache flow enable on a Fast ethernet interface


tanks one more time


sh processes switching example

Drops RP 0 SP 0

SPD Flushes Fast 0 SSE 0

SPD Aggress Fast 0

SPD Priority Inputs 44 Drops 0


Protocol Path Pkts In Chars In Pkts Out Chars Out

Other Process 0 0 22019 528456

Cache misses 0

Fast 0 0 0 0

Auton/SSE 0 0 0 0

IP Process 34997 3486135 14760 2317463

Cache misses 34997

Fast 10127390 1619932064 4930614 2763202294

Auton/SSE 0 0 0 0

CDP Process 3673 1160668 3674 1109548

Cache misses 0

Fast 0 0 0 0

Auton/SSE 0 0 0 0


DALE FRANCIS Wed, 11/20/2002 - 03:59
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Depending on what code you are using CEF should be enabled by defualt: The Eg: below i have configured both but i am not exporting flows as i do not have a collector.


interface Ethernet3/0

ip address 192.168.0.2 255.255.255.0

ip route-cache flow

crypto map test



sh ip int eth 3/0

Ethernet3/0 is up, line protocol is up

Internet address is 192.168.0.2/24

Broadcast address is 255.255.255.255

Address determined by setup command

MTU is 1500 bytes

Helper address is not set

Directed broadcast forwarding is disabled

Outgoing access list is not set

Inbound access list is not set

Proxy ARP is enabled

Security level is default

Split horizon is enabled

ICMP redirects are always sent

ICMP unreachables are always sent

ICMP mask replies are never sent

IP fast switching is enabled

IP fast switching on the same interface is disabled

IP Flow switching is enabled

IP CEF switching is enabled

IP Flow switching turbo vector

IP Flow CEF switching turbo vector

IP multicast fast switching is enabled

IP multicast distributed fast switching is disabled


As for the output of the sh interface swtiching, you should see a line that says fast, the IP process line shows the amount of process switching that is done, those are the counters to watch out for, as far as you needing the flow information you will have to stick to ip route-cache flow, however i would look at turning on CEF too.



bs0000554 Wed, 11/20/2002 - 04:28
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dear Dale,

To enable flow-switching you need to have the command

ip flow-cache feature-accelerate enable in the router

anf the ip route-cache flow command in the interface

To export you have to have also

ip flow-export destination

ip flow-export source

ip flow-export version 5


tank you for the other replies



DALE FRANCIS Wed, 11/20/2002 - 04:38
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Thanks for your input, i am very well aware all i was saying is i do not have a collector so hence did not config export portion. I was just showing that CEF and FLOW can run together and hence.. should help your cause.. So basically enable CEF.. i am sure would help..

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