Throttle count is 0 but RP drop count is very high?

[samarjitdas]

Hi, in which scenario below statistic is found. Throttle count is 0 but RP drop count is very high?

sh int fastEthernet 1/11 switching

FastEthernet1/11

          Throttle count          0

                   Drops         RP    1279481         SP          0

             SPD Flushes       Fast          0        SSE          0

             SPD Aggress       Fast          0

            SPD Priority     Inputs    2259325      Drops          0

Protocol  IP

          Switching path    Pkts In   Chars In   Pkts Out  Chars Out

                 Process    5378079  414430575    3801435  274155501

            Cache misses          0          -          -          -

                    Fast 2254173747 3858907738 1256063247 3802373208

               Auton/SSE          0          0          0          0

[nkarpysh]

Hello,

So RP drops mean that packets coming on that int were sent to CPU for some reason. And CPU then took a decision to drops those. Throttle are drops when CPU buffer is full and it needs to clear all packets.

CPU might have other reasons to drop those packets. E.G. some options set CPU does not understand, TTL expired, and some other reasons. So you need to see those packets to see why they are sent to CPU and then dropped.

You can do either SPAN or netdr (debug netdr cap rx, show netdr cap)

Nik

[samarjitdas]

Hi Nik

I was troubleshooting an issue with Cisco 3845 router.The connectivity is as below,

Router has five interfaces(Fe) connected with C2950 switch and they are assigned with different IP subnet. All ports of

C2950  switch are in default VLAN 1 and furtherC2950 switch is connected with 5  L3 switches. All ports of L3 switches are also in default VLAN 1 but  servers are assigned with different IP pool as servers are connected to  different switches.

I know there are flaws with the design but as per customer's query I have to troubleshoot and provide the exact root cause.Sometimes I experience ping drop from router to one of the subnet and it gets resolved automatically after sometimes.When I collected data from this router, i could see huge packet drop in input queque as well as in output queque but not able to find out the real reason of such drops in queque. I ran the show int fax/y switching command in router and could gathered some drop in RP.  Can you please put some lights to trobleshoot this issue.

[nkarpysh]

Hello,

Can you please describe the router model and IOS. AS I said before - Input RP drops are usually due to some packets which CPU decided to drop (many times TTL=1). So it is needed to catch those packets and eliminate those from network.

The problem is that as you said this behaviour intermittent - so we need to TS it when it is happening. One of the ways is to setup SPAN on the affected port and capture RX packets and see what those are - so you can configure that and start capture when problem starts.

Other ways I can advise based on the router HW and SW versions.

Nik

[samarjitdas]

Hi Nik

Ok.I am going to configure the SPAN on the affacted port and will take etheral capture in the time of problem occurs.I will take the TS when it heppens again.

Please find the H/W & S/W version of router.

sh version

Cisco IOS Software, 3800 Software (C3845-IPBASE-M), Version 12.4(17b), RELEASE SOFTWARE (fc2)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 1986-2008 by Cisco Systems, Inc.

Compiled Tue 26-Feb-08 08:47 by prod_rel_team

ROM: System Bootstrap, Version 12.4(13r)T10, RELEASE SOFTWARE (fc1)

TELCORDIA-RTR-DL-01 uptime is 48 weeks, 6 days, 21 hours, 36 minutes

System returned to ROM by bus error at PC 0x60A40620, address 0xD0D0D0D at 08:08:03 UTC Wed Dec 22 2010

System image file is "flash:c3845-ipbase-mz.124-17b.bin"

Cisco 3845 (revision 1.0) with 223232K/38912K bytes of memory.

Processor board ID FHK1305F27E

16 FastEthernet interfaces

2 Gigabit Ethernet interfaces

4 Serial interfaces

2 Channelized E1/PRI ports

DRAM configuration is 64 bits wide with parity enabled.

479K bytes of NVRAM.

62720K bytes of ATA System CompactFlash (Read/Write)

Configuration register is 0x2102