Cisco IOS-XR Input Drops: NP Counter Troubleshooting

Input drops on Cisco IOS XR platforms confuse many engineers who are used to classic IOS, because in XR there is no single input-queue definition that explains the counter. Instead, the input drop counter aggregates drops reported by different components, and the most common source on an ASR 9000 is the Network Processor (NP) on the ingress line card. This guide explains why IOS XR input drops behave differently, shows the show commands that pinpoint the cause, and walks through a structured packet-drop troubleshooting workflow.

Why IOS XR Input Drops Differ from Cisco IOS

In classic Cisco IOS, an input drop normally means the interface input queue filled up because too many packets were punted to the CPU. In IOS XR there is no such strict definition: each software or hardware component decides independently whether a drop increments the interface input drop counter. As a result, "input drops" on an XR router can be caused by unknown destination MACs, VLAN mismatches on subinterfaces, NP microcode drops, or even legitimate feature behavior such as dropping frames for features that are not configured.

Common Causes of Input Drops on ASR 9000

• Unknown DMAC or dot1q VLAN: frames with a destination MAC that does not belong to the router, or with a VLAN that no subinterface matches. L2 flooding in the broadcast domain and Ethernet keepalives from legacy Cisco IOS routers are typical triggers.
• NP microcode drops: the Network Processor drops packets for reasons such as IPv4 sanity/address checksum failures, martian source addresses, or MPLS leaf no-match conditions.
• Misprogrammed CEF adjacency: a forwarding entry that does not point to a valid adjacency causes NP drops that surface as interface input drops.
• Punt-path oversubscription: control-plane bound traffic exceeding the line card's punt rate.

Key Show Commands for Input Drop Troubleshooting

Start at the interface level and then drill into the NP statistics. On an ASR 9000 running IOS XR, the useful commands are:

RP/0/RSP0/CPU0:router# show interfaces GigabitEthernet0/0/0/18
RP/0/RSP0/CPU0:router# show interfaces GigabitEthernet0/0/0/18.1
RP/0/RSP0/CPU0:router# show controllers np ports all location 0/0/CPU0
RP/0/RSP0/CPU0:router# show controllers np counters all location 0/0/CPU0
RP/0/RSP0/CPU0:router# show controllers np counters np0 location 0/0/CPU0

The show controllers np ports command maps each front-panel interface to its NP and port number, so you know which NP statistics belong to the interface that reports drops. show controllers np counters then exposes the detailed NP drop counters; not every counter in this output indicates a problem, because many counters also track normal traffic.

Using the NP Microcode Capture

When a specific NP counter is incrementing, capture the actual dropped packets to confirm the root cause. The microcode capture feature shows a snapshot of the packets that hit a given NP drop reason:

RP/0/RSP0/CPU0:router# show controllers np capture np1 location 0/0/CPU0

The output includes the drop reason (for example RSV_DROP_MPLS_LEAF_NO_MATCH or an IPv4 checksum failure) and a hex dump of the packet, which tells you the source interface and the exact header that triggered the drop.

Recommended Troubleshooting Workflow

1. Clear the counters so you start from a clean slate:

   RP/0/RSP0/CPU0:router# clear counters all
   RP/0/RSP0/CPU0:router# clear controller np counters all

2. Reproduce the traffic pattern that caused the drop and re-check show interfaces to confirm the input drop counter is still increasing.
3. Run show controllers np counters all location on the affected line card and identify which counter moves at the same rate as the interface input drop counter.
4. If the cause is not obvious, use the NP capture to inspect a dropped packet, then fix the root cause (filter the offending MAC/VLAN, correct the feature configuration, or escalate a suspected hardware/software bug with the captured evidence).

Related reading: Cisco ASR9000 fabric troubleshooting show commands and Cisco ASR9000 troubleshooting show commands for IOS-XR.

Original article: https://community.cisco.com/t5/service-providers-knowledge-base/asr9000-xr-troubleshooting-packet-drops-and-understanding-np/tac-p/3126735 | Cisco: Troubleshoot Input Drops in IOS XR