The decision to redirect the packet for ICMP redirect is done using a bit in the PFC HW and it is a per-vlan bit, and not per flow. This bit can either be on or off and is controlled by having '<no> ip redirects'. That is why you are seeing all traffic in the vlan getting punted to software, if we don't have 'no ip redirects' configured.
sukumar On Wed, 9 May 2007, Church, Charles wrote: > I don't think the PFC has any logic in it to provide ICMP responses for > any of the message types. Someone from Cisco would know for sure > though. Without the ability for the PFC to respond, those packets would > get forwarded to the MSFC. It seems that it should only do it once per > flow, but it sounds like it was doing it for all the traffic, since your > CPU went down so dramatically. > > > Chuck Church > Multimax Principal Network Engineer, CCIE #8776 > EDS Contractor, Multimax - Navy Marine Corps Intranet (NMCI) > 1210 N. Parker Rd. | Greenville, SC 29609 > Office: 864-335-9473 | Cell: 864-266-3978 > [EMAIL PROTECTED] > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of barney gumbo > Sent: Wednesday, May 09, 2007 5:39 PM > To: [email protected] > Subject: Re: [c-nsp] troubleshooting SVI input drops on MSFC3 > > I disabled IP redirects on the SVI and traffic is no longer seen on the > SVI interface, no longer seeing SVI input drops, and CPU returned to > normal. > > Why does the router sending an IP redirect cause traffic to hit the > MSFC? > > Or, does the traffic hit the MSFC because the CEF adjacency is the same > interface for all prefixes, i.e. router-on-a-stick? > > I've read references to both as being the reason one would see high CPU > on an MSFC along with SVI input drops, just trying to understand the > hardware better. It seems the magic number is around 40-50 Mbps which > resulted in 75% CPU usage and input drops. That just seems low for such > powerful hardware... > > > On 5/9/07, barney gumbo <[EMAIL PROTECTED]> wrote: >> >> I see ICMP redirects (which is not disabled on that SVI) and they are >> incrementing. I can understand high CPU as a result of the router >> being forced to trx alot of ICMP redirects, however that (the MSFC >> sending ICMP >> redirects) doesnt cause the traffic to be process-switched, does it? >> >> ICMP statistics: >> Rcvd: 0 format errors, 0 checksum errors, 0 redirects, 318 > unreachable >> 10817442 echo, 3142088 echo reply, 0 mask requests, 0 mask >> replies, 0 quench >> 0 parameter, 0 timestamp, 0 info request, 0 other >> 0 irdp solicitations, 0 irdp advertisements >> Sent: 115887 redirects, 2262 unreachable, 3144305 echo, 10817442 >> echo reply >> 0 mask requests, 0 mask replies, 0 quench, 0 timestamp >> 0 info reply, 1740292 time exceeded, 0 parameter problem >> 0 irdp solicitations, 0 irdp advertisements >> >> >> ICMP statistics: >> Rcvd: 0 format errors, 0 checksum errors, 0 redirects, 318 > unreachable >> 10820192 echo, 3142088 echo reply, 0 mask requests, 0 mask >> replies, 0 quench >> 0 parameter, 0 timestamp, 0 info request, 0 other >> 0 irdp solicitations, 0 irdp advertisements >> Sent: 115939 redirects, 2262 unreachable, 3144305 echo, 10820192 >> echo reply >> 0 mask requests, 0 mask replies, 0 quench, 0 timestamp >> 0 info reply, 1740292 time exceeded, 0 parameter problem >> 0 irdp solicitations, 0 irdp advertisements >> >> >> On 5/9/07, Church, Charles <[EMAIL PROTECTED]> wrote: >>> >>> Sending ICMP redirects for all those? >>> >>> Chuck >>> >>> --- Original Message --- >>> From:"barney gumbo" <[EMAIL PROTECTED]> Sent:Wed 5/9/07 12:15 >>> pm To:"Dale W. Carder" <[EMAIL PROTECTED]> >>> Cc:"[email protected]" < [email protected]> >>> Subj:Re: [c-nsp] troubleshooting SVI input drops on MSFC3 >>> >>> I have a little more info this time.. >>> >>> It appears that the traffic is being process switched. >>> >>> It started when this switch became more of a "router on a stick". >>> Previously most traffic flowed from one SVI to the other; this 6503 >>> is essentially an access or WAN router. Now traffic flows from >>> routers on the same VLAN into the SVI and then back out of the SVI >>> to get to the next hop, which is a firewall, all on the same VLAN. >>> >>> It seems like once the flow volume hits around 40 Mbps, the input >>> drops begin. >>> >>> Going away from the router-on-a-stick design, where the bulk of the >>> traffic transit's across the switch instead of in/out the same >>> interface, is not a trivial change, so I would like to try and get >>> some confidence that this is related to the problem before I start >>> to make changes. This is all just a guess, but it's the only major >>> thing that has changed in the last week. >>> >>> Any ideas if this could be my cause of process-switchng and input > drops? >>> >>> Any ideas on how I can verify the router-on-a-stick forwarding is >>> definitely to blame? >>> >>> On 5/9/07, Dale W. Carder <[EMAIL PROTECTED]> wrote: >>>> >>>> >>>> Here's some commands to get you started: >>>> >>>> sh buffers input-interface >>>> sh int vlan1234 switching >>>> sh ip interface >>>> sh ip traffic >>>> sh cef drop >>>> sh ip cache flow >>>> sh cef not-cef-switched >>>> >>>> Some more help can be found here: >>>> http://www.cisco.com/warp/public/63/queue_drops.html >>>> >>>> You also might want to verify that you didn't configure a feature >>>> that causes punts. >>>> >>>> If you really want to get dirty, you can create a span session to >>>> monitor traffic destined to the RP. This has been discussed on >>>> this list once or twice, but it is a bit messy. >>>> >>>> Dale >>>> >>>> >>>> On May 9, 2007, at 9:43 AM, barney gumbo wrote: >>>> >>>>> I am seeing high input interface drops on an SVI interface on an > >>>>> MSFC3. The >>>>> MSFC3 is installed in a 6503 chassis with Sup720. The switch is > >>>>> running hybird mode. >>>>> >>>>> The traffic load has increased, and CPU is running high when the > >>>>> traffic load increases. I don't know why the SVI is showing >>>>> increased traffic load because normally I don't see traffic >>>>> through the SVI, it all get's >>> MLS >>>>> switched. Something in the last week has caused traffic to be >>>>> switched through the SVI showing the high input drops. The >>>>> overal load of traffic which should be routed (MLS switched) via > >>>>> the interface has not increased or decreased; all of a sudden in > >>>>> the last week traffic is being >>>>> (seemingly) >>>>> process switched through this SVI. >>>>> >>>>> Where do I begin troubleshooting high interface drops on an SVI? >>>> >>> _______________________________________________ >>> cisco-nsp mailing list [email protected] >>> https://puck.nether.net/mailman/listinfo/cisco-nsp >>> archive at http://puck.nether.net/pipermail/cisco-nsp/ >>> >> >> > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ > > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ > _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
