Packet drops

This document provides information about packet drops on the Cisco ASR 1000 Series Aggregation Services Routers.

Packet drops

Packet drops are a network event that

  • occur when network devices cannot forward incoming packets due to resource limitations,

  • result from insufficient buffer space, CPU overload, or network congestion, and

  • impact application performance by causing delays or disconnects.

During a period of high CPU utilization on a Cisco ASR 1000 router, packets destined for a specific interface are dropped once the buffer exceeds its capacity, resulting in application disconnects.

Packet drops occur when a router or network device fails to forward packets to their intended destination, resulting in lost data within the network. Packet drops can significantly impact network performance and application responsiveness, especially for real-time or UDP-based applications that do not have retransmission mechanisms.

Packet drop diagnostics

This section outlines information on packet drop diagnostics.

From Cisco IOS XE 17.6, you can run the show drops command to troubleshoot the root cause of packet drops. Using the show drops command, you can identify the following items:

  • The root cause of a packet drop based on the feature or the protocol.

  • The history of the Quantum Flow Processor drops.

View packet drop information

Packet drops can indicate areas where traffic is not processed as expected. You can use these commands to identify drop types, as well as affected interfaces, features, or protocols.

Procedure

Step 1

enable

Example:

Router> enable

Enable privileged EXEC mode. Enter your password if prompted.

Step 2

show drops

Example:

Router# show drops

Displays the drop statistics.

Step 3

show drops { bqs | crypto | firewall | interface | ip-all | nat | punt | qfp | qos | history }

Example:

Router# show drops qfp
Displays the drop statistics and provides a summary for the chosen interface or protocol.

Note

 

From Cisco IOS XE 17.13.1a, a new keyword option history is added to the show drops command. You can use the show drops history qfp command to view the history of QFP drops.

You see lists and summaries of packet drop statistics that help you identify where drops are occurring. This information supports troubleshooting and configuration adjustments.

The following is a sample output of the show drops command. This sample output displays the packet drops information related to the Quantum Flow Processor (QFP). 

Router# show drops
bqs BQS related drops
crypto IPSEC related drops
firewall Firewall related drops
history History of drops
interface Interface drop statistics
ip-all IP related drops
nat NAT related drops
punt Punt path related drops
qfp QFP drop statistics
qos QoS related drops
| Output modifiers
<cr> <cr>
Router# show drops qfp
show platform hardware qfp active statistics drop detail
Last clearing of QFP drops statistics : Fri Feb 18 08:02:37 2022
(6d 23h 54m 29s ago)
------------------------------------------------------------------
ID Global Drop Stats Packets
Octets
------------------------------------------------------------------
319 BFDoffload 9
1350
61 Icmp 84
3780
53 IpFragErr 32136
48718168
244 IpLispHashLkupFailed 3
213
56 IpsecInput 18
4654
23 TailDrop 26713208
10952799454
216 UnconfiguredIpv6Fia 241788
26596680
show platform hardware qfp active interface all
statistics drop_summary
----------------------------------------------------------------
Drop Stats Summary:
note: 
1) these drop stats are only updated when PAL
reads the interface stats.
2) the interface stats include the subinterface
Interface Rx Pkts Tx Pkts
-----------------------------------------------------------------
GigabitEthernet1 60547 0
GigabitEthernet2 60782 27769658
GigabitEthernet3 60581 0
GigabitEthernet4 60502 1323990
Tunnel14095001 0 1990214
Tunnel14095002 0 3883238
Tunnel14095003 0 3879243
Tunnel14095004 0 2018866
Tunnel14095005 0 3875972
Tunnel14095006 0 3991497
Tunnel14095007 0 4107743
Tunnel14095008 0 3990601

Commands for viewing packet drop information

This section provides examples of command output used to verify packet information. To view drop statistics for all interfaces in Packet Processor Engine, use the show drops qfp command.

Note

The wrapper command show drops qfp is the shorthand notation for the original show platform hardware qfp active statistics drop command. 

Router# show drops qfp
-----------------------------------------
Global Drop Stats Octets
Packets
-----------------------------------------
AttnInvalidSpid 0 0
BadDistFifo 0 0
BadIpChecksum 0 0

To view the history of QFP drops for all interfaces in Packet Processor Engine, use the show drops history qfp command. This command can also track the number of packet drops in the last 1 minute, 5 minute, and 30 minute time period.


Note

The wrapper command show drops history qfp is the shorthand notation for the original show platform hardware qfp active statistics drop history command.


Note

The wrapper command show drops history qfp is not available on Catalyst 8500L Edge Platform. 

Router# show drops history qfp
Last clearing of QFP drops statistics : Mon Jun 26 07:29:14
2023
(21s ago)
--------------------------------------------------------------
Global Drop Stats 1-Min
5-Min 30-Min All
--------------------------------------------------------------
Ipv4NoAdj 0
0 0 99818
Ipv4NoRoute 0
0 0 99853

Packet drop warning thresholds

Sample warning messages

From Cisco IOS XE 17.14, you can configure the warning thresholds for packet drops, either for each drop cause or for the total QFP drop rate, using packets per second as the threshold value. If the configured thresholds are exceeded, then a rate-limited syslog warning is generated. One warning is generated if the total threshold is exceeded, and an additional warning is generated for each drop cause that exceeds its threshold.

The warning is generated a maximum of once per minute for each drop cause. The drops over the previous minute are checked against the threshold (packets per second) x 60, and if the drops exceed this value, a warning is generated.

These are sample warnings for total and individual drop causes.

%QFP-5-DROP_OVERALL_RATE: Exceeded the overall drop threshold 10000 pps during the last 60-second measurement period, packets dropped in last 1 minute: 641220, last 5 minutes: 1243420, last 30 minutes: 124342200
%QFP-5-DROP_CAUSE_RATE: Exceeded the drop threshold 1000 pps for QosPolicing (drop code: 20) during the last 60-second measurement period, packets dropped due to QosPolicing in last 1 minute: 61220, last 5 minutes: 43420, last 30 minutes: 4611200

Configure packet drop warning threshold

Use this procedure when you want to receive alerts for excessive packet drops in the platform's Quantum Flow Processor.

Procedure

Step 1

enable

Example:

Router> enable

Enables the privileged EXEC mode. Enter your password if prompted.

Step 2

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

platform qfp drops threshold { per-causedrop_idthreshold | totalthreshold }

Example:

Router# platform qfp drops threshold per-cause 206 10

Specifies the threshold value for each drop cause or the total.

Note

 

Use the show platform hardware qfp active statistics drop detail command to view the drop cause ID.

You receive a warning when packet drop counts exceed the configured thresholds.

The following example shows how to configure the warning threshold of 15 pps for drop cause ID 24. 
Router> enable 
Router# configure terminal 
Router(config)# platform qfp drops threshold  
per-cause Set warning threshold for per cause QFP drops 
total Set warning threshold for total QFP drops
Router(config)#platform qfp drops threshold per-cause ? 
<0-1024> QFP drop cause ID
Router(config)# platform qfp drops threshold per-cause 24 ? 
<0-2147483647> Drop threshold in packets per second (pps)
Router(config)# platform qfp drops threshold per-cause 24 15
The following example shows how to configure the warning threshold of 100 pps for total QFP drops. 
Router> enable 
Router# configure terminal 
Router(config)# platform qfp drops threshold 
per-cause Set warning threshold for per cause QFP drops 
total Set warning threshold for total QFP drops
Router(config)# platform qfp drops threshold total ? 
<0-2147483647> Drop threshold in packets per second (pps)
Router(config)# platform qfp drops threshold total 100

View packet drop warning thresholds

Identify and display the configured warning thresholds for packet drops by cause and for total QFP drops.

Procedure

Step 1

enable

Example:

Router> enable

Enables the privileged EXEC mode. Enter your password if prompted.

Step 2

show platform hardware qfp active statistics drop threshold

Example:

Router# show platform hardware qfp active statistics drop thresholds

Displays the configured warning thresholds for each drop cause and for total QFP drops.

Note

 

  • The wrapper command show drops thresholds is the shorthand notation of the show platform hardware qfp active statistics drop threshold command.

  • The wrapper command show drops thresholds is currently not available on Catalyst 8500L Edge Platform.

You can view the warning threshold values for each drop cause and the total. These values help you monitor and troubleshoot packet drop events.

The following is a sample output of the show platform hardware qfp active statistics drop threshold command.
Router# show platform hardware qfp active statistics drop thresholds 
------------------------------------------------------ 
Drop ID         Drop Cause Name             Threshold 
------------------------------------------------------ 
10             BadIpChecksum                 100 
206            PuntPerCausePolicerDrops      10
20             QosPolicing                   200 
                Total                        30
The following is a sample output of the show drops thresholds wrapper command.
Router# show platform hardware qfp active statistics drop thresholds 
------------------------------------------------------ 
Drop ID         Drop Cause Name             Threshold 
------------------------------------------------------ 
10             BadIpChecksum                 100 
206            PuntPerCausePolicerDrops      10
20             QosPolicing                   200 
                Total                        30