Cisco - ip route-cache and CEF

11-17-2003, 04:02 AM

Hi,

I have a router that has the commands "no ip route-cache" and "no ip
mroute-cache" configured on a fast ethernet interface. Also it has ip
cef enabled globally. However when i run a sh int fast 0/0 switching i
get the following output

FastEthernet0/0
Throttle count 0
Drops RP 0 SP 0
SPD Flushes Fast 0 SSE 0
SPD Aggress Fast 0
SPD Priority Inputs 18950 Drops 0

Protocol Path Pkts In Chars In Pkts Out Chars Out
Other Process 1423347 234346884 705153 45129792
Cache misses 0
Fast 0 0 0 0
Auton/SSE 0 0 0 0
IP Process 100215903 2862729521 14758204 1992377675
Cache misses 0
Fast 528073360 434219695 424384892 1205328132
Auton/SSE 0 0 0 0
IPX Process 7865372 2565113786 14 4988
Cache misses 0
Fast 0 0 0 0
Auton/SSE 0 0 0 0
DEC MOP Process 0 0 11735 903595
Cache misses 0
Fast 0 0 0 0
Auton/SSE 0 0 0 0
Spanning Tree Process 7042141 450697024 0 0
Cache misses 0
Fast 0 0 0 0
Auton/SSE 0 0 0 0
ARP Process 39598 2375880 10453 668992
Cache misses 0
Fast 0 0 0 0
Auton/SSE 0 0 0 0
CDP Process 117514 50883544 117532 37727772
Cache misses 0
Fast 0 0 0 0
Auton/SSE 0 0 0 0

My understanding was that with the "no ip route-cache" command all
packets would be process switched, but above i can see the
fast-switched counter increase.

Does anyone know why?

Thanks

Kenny D

11-17-2003, 06:12 PM

(Kenny D) wrote in
news: om:

> Hi,
>
> I have a router that has the commands "no ip route-cache" and "no ip
> mroute-cache" configured on a fast ethernet interface. Also it has ip
> cef enabled globally. However when i run a sh int fast 0/0 switching i
> get the following output
>
> [snip
>
> My understanding was that with the "no ip route-cache" command all
> packets would be process switched, but above i can see the
> fast-switched counter increase.
>
> Does anyone know why?
>
> Thanks
>

According to this page:

http://www.cisco.com/en/US/products/...ucts_tech_note
09186a00801d6038.shtml

Look at the table with "Incoming Interface / Outgoing Interface /
Switching Method". It looks like it still uses fast switching when going
Process to CEF.

Quote:

In other words, you need CEF to be enabled on the incoming interface for
packets to be CEF switched, and since CEF makes the forwarding decision
on input, use the no ip route-cache cef command on the ingress interface
to disable CEF. In contrast, since Cisco IOS builds a fast-switching
cache entry after switching a packet, a packet coming in on a process-
switched interface and going out through a fast-switched interface will
be fast switched, use the no ip route-cache command on the egress
interface to disable fast switching.

--
Joe Drago
StreamLine Communications

11-18-2003, 01:33 AM

On 16 Nov 2003 21:02:42 -0800, (Kenny D)
wrote:

>Hi,
>
>I have a router that has the commands "no ip route-cache" and "no ip
>mroute-cache" configured on a fast ethernet interface. Also it has ip
>cef enabled globally. However when i run a sh int fast 0/0 switching i
>get the following output
>....
>My understanding was that with the "no ip route-cache" command all
>packets would be process switched, but above i can see the
>fast-switched counter increase.
>
>Does anyone know why?

My understanding is that the 'show int switching' command currently
doesn't distinguish between fast-switched and CEF-switched packets, so
CEF-switched packets are recorded as being fast-switched.

-Terry

11-19-2003, 09:43 PM

On Mon, 17 Nov 2003 21:33:45 -0500, Terry Baranski wrote:
> On 16 Nov 2003 21:02:42 -0800, (Kenny D)
> wrote:
>
>>Hi,
>>
>>I have a router that has the commands "no ip route-cache" and "no ip
>>mroute-cache" configured on a fast ethernet interface. Also it has ip
>>cef enabled globally. However when i run a sh int fast 0/0 switching i
>>get the following output
>>....
>>My understanding was that with the "no ip route-cache" command all
>>packets would be process switched, but above i can see the
>>fast-switched counter increase.
>>
>>Does anyone know why?
>
> My understanding is that the 'show int switching' command currently
> doesn't distinguish between fast-switched and CEF-switched packets, so
> CEF-switched packets are recorded as being fast-switched.

show adj detail

Will show how many packets/bytes are CEF switched out of each
next-hop/adjacency

--
Jesper Skriver, CCIE #5456, FreeBSD committer

Nan · 09-06-2007, 10:31 PM

6500, CatoS, MSFC2. On most of our vlan interfaces we have:
no ip route-cache and no ip mroute-cache. We are enabling multicasting throughout the LAN but just wanted to know if there were any issues removing these commands? It is my understanding that removing these enables fast switching on the interface. It sounds like a good thing to me but why are they there in the first place????
Thanks.

11-17-2003, 06:12 PM	#2
Joe Drago Posts: n/a	Re: ip route-cache and CEF (Kenny D) wrote in news: om: > Hi, > > I have a router that has the commands "no ip route-cache" and "no ip > mroute-cache" configured on a fast ethernet interface. Also it has ip > cef enabled globally. However when i run a sh int fast 0/0 switching i > get the following output > > [snip > > My understanding was that with the "no ip route-cache" command all > packets would be process switched, but above i can see the > fast-switched counter increase. > > Does anyone know why? > > Thanks > According to this page: http://www.cisco.com/en/US/products/...ucts_tech_note 09186a00801d6038.shtml Look at the table with "Incoming Interface / Outgoing Interface / Switching Method". It looks like it still uses fast switching when going Process to CEF. Quote: In other words, you need CEF to be enabled on the incoming interface for packets to be CEF switched, and since CEF makes the forwarding decision on input, use the no ip route-cache cef command on the ingress interface to disable CEF. In contrast, since Cisco IOS builds a fast-switching cache entry after switching a packet, a packet coming in on a process- switched interface and going out through a fast-switched interface will be fast switched, use the no ip route-cache command on the egress interface to disable fast switching. -- Joe Drago StreamLine Communications

11-18-2003, 01:33 AM	#3
Terry Baranski Posts: n/a	Re: ip route-cache and CEF On 16 Nov 2003 21:02:42 -0800, (Kenny D) wrote: >Hi, > >I have a router that has the commands "no ip route-cache" and "no ip >mroute-cache" configured on a fast ethernet interface. Also it has ip >cef enabled globally. However when i run a sh int fast 0/0 switching i >get the following output >.... >My understanding was that with the "no ip route-cache" command all >packets would be process switched, but above i can see the >fast-switched counter increase. > >Does anyone know why? My understanding is that the 'show int switching' command currently doesn't distinguish between fast-switched and CEF-switched packets, so CEF-switched packets are recorded as being fast-switched. -Terry

11-19-2003, 09:43 PM	#4
Jesper Skriver Posts: n/a	Re: ip route-cache and CEF On Mon, 17 Nov 2003 21:33:45 -0500, Terry Baranski wrote: > On 16 Nov 2003 21:02:42 -0800, (Kenny D) > wrote: > >>Hi, >> >>I have a router that has the commands "no ip route-cache" and "no ip >>mroute-cache" configured on a fast ethernet interface. Also it has ip >>cef enabled globally. However when i run a sh int fast 0/0 switching i >>get the following output >>.... >>My understanding was that with the "no ip route-cache" command all >>packets would be process switched, but above i can see the >>fast-switched counter increase. >> >>Does anyone know why? > > My understanding is that the 'show int switching' command currently > doesn't distinguish between fast-switched and CEF-switched packets, so > CEF-switched packets are recorded as being fast-switched. show adj detail Will show how many packets/bytes are CEF switched out of each next-hop/adjacency -- Jesper Skriver, CCIE #5456, FreeBSD committer

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11-17-2003, 04:02 AM	#1
	ip route-cache and CEF Hi, I have a router that has the commands "no ip route-cache" and "no ip mroute-cache" configured on a fast ethernet interface. Also it has ip cef enabled globally. However when i run a sh int fast 0/0 switching i get the following output FastEthernet0/0 Throttle count 0 Drops RP 0 SP 0 SPD Flushes Fast 0 SSE 0 SPD Aggress Fast 0 SPD Priority Inputs 18950 Drops 0 Protocol Path Pkts In Chars In Pkts Out Chars Out Other Process 1423347 234346884 705153 45129792 Cache misses 0 Fast 0 0 0 0 Auton/SSE 0 0 0 0 IP Process 100215903 2862729521 14758204 1992377675 Cache misses 0 Fast 528073360 434219695 424384892 1205328132 Auton/SSE 0 0 0 0 IPX Process 7865372 2565113786 14 4988 Cache misses 0 Fast 0 0 0 0 Auton/SSE 0 0 0 0 DEC MOP Process 0 0 11735 903595 Cache misses 0 Fast 0 0 0 0 Auton/SSE 0 0 0 0 Spanning Tree Process 7042141 450697024 0 0 Cache misses 0 Fast 0 0 0 0 Auton/SSE 0 0 0 0 ARP Process 39598 2375880 10453 668992 Cache misses 0 Fast 0 0 0 0 Auton/SSE 0 0 0 0 CDP Process 117514 50883544 117532 37727772 Cache misses 0 Fast 0 0 0 0 Auton/SSE 0 0 0 0 My understanding was that with the "no ip route-cache" command all packets would be process switched, but above i can see the fast-switched counter increase. Does anyone know why? Thanks Kenny D

09-06-2007, 10:31 PM	#5
Nan Junior Member Join Date: Sep 2007 Posts: 1	ip route-cache issues 6500, CatoS, MSFC2. On most of our vlan interfaces we have: no ip route-cache and no ip mroute-cache. We are enabling multicasting throughout the LAN but just wanted to know if there were any issues removing these commands? It is my understanding that removing these enables fast switching on the interface. It sounds like a good thing to me but why are they there in the first place???? Thanks.