Dropped Packet Notifications to Aid in System Performance Tuning
The dropped-packet notification feature enables you to see detailed information about what is causing particular packet drops. Having that information, in real time, allows you to tune up your system’s performance.
Dropped-Packet Notifications
Packet drops are common occurrences on network switches and routers. Debugging packet drops can be complex and time-consuming. The packet-processing pipeline supports a limited set of drop counters, but these counters are insufficient for debugging complex packet-drop issues. Debugging difficulties can result in high mean times to recovery (MTTRs).
A feature called dropped-packet notification, also referred to as mirror on drop (MoD), can help you debug packet drops in real time. These types of packet drops are monitored:
-
Stateless ingress—Packets dropped due to processing in the ingress pipeline
-
Stateless MMU—Packets dropped due to congestion in the MMU
Packets that are dropped by the IP and MMU are sampled for mirroring so that they do not overwhelm regular network traffic.
The dropped-notification feature generates reports for the drops in PSAMP format and sends them to a third-party entity, such as a collector.
Meta information—such as packet-drop reason and the congestion point (switch, port, or queue)—about the dropped packet is carried in the PSAMP file, and only the first cell of the packet is mirrored.
Samples of Dropped-Packet Notification Configurations
You configure much of the dropped-packet notification feature at the
[edit forwarding-options mirror-profile] hierarchy
level.
In the following sample configurations, all commands are optional except for the first one, for the switch ID.
Stateless MMU flow-unaware mode ( [edit forwarding-options
analyzer] hierarchy):
user@host# set forwarding-options switch-id id-value-range user@host# set forwarding-options mirror-profile profile-name mirror-on-drop modtype stateless user@host# set forwarding-options mirror-profile profile-name mirror-on-drop mmu user@host# set forwarding-options mirror-profile profile-name mirror-on-drop mmu sample-rate integer-value user@host# set forwarding-options mirror-profile profile-name mirror-on-drop mmu drop-reasons drop-reasons-list
Drop-reason options for MMU dropped-packet notifications:
-
ingress-limit -
egress-queue-limit -
egress-wred-drop
Stateless ingress flow-unaware mode ([edit forwarding-options
analyzer] hierarchy):
The ingress configuration is the same as for the MMU configuration except for the following ingress- specific configuration:
user@host# set forwarding-options mirror-profile profile-name mirror-on-drop ingress
By default, the 18 currently supported L3 ingress drop reasons are enabled internally.
Also by default, a sampling threshold value of 0 (zero) is used internally—all packets that are dropped are mirrored to the collector.