Network management software found that ifInDiscards node count statistics continue to increase on switches

Not involving

The customer found on the network management software that the H3C switch had a problem of increasing ifInDiscards node count statistics, but the actual check on the device did not find any packet loss, nor did it affect the business.

The ifInDiscards node on the H3C switch only indicates the discard count of the upper-layer protocol packets that the device itself thinks should not be processed by it or the unreasonable packets sent to the CPU for processing. It has nothing to do with the forwarded service data packet, so its statistical value has no practical meaning and does not affect the normal operation of the device.

The analysis of the ifInDiscards node is described as follows.

.1.3.6.1.2.1.2.2.1.13

ifInDiscards OBJECT-TYPE

  -- FROM       IF-MIB, RFC1213-MIB

  SYNTAX        Counter32

  MAX-ACCESS       read-only

  STATUS        current

  DESCRIPTION      "The number of inbound packets which were chosen to be

            discarded even though no errors had been detected to prevent

            their being deliverable to a higher-layer protocol.  One

            possible reason for discarding such a packet could be to

            free up buffer space.

            Discontinuities in the value of this counter can occur at

            re-initialization of the management system, and at other

            times as indicated by the value of

            ifCounterDiscontinuityTime."

::= { iso(1) org(3) dod(6) internet(1) mgmt(2) mib-2(1) interfaces(2) ifTable(2) ifEntry(1) 13 }

inDiscards contains two reasons for discarding packets:

1. Statistics of packet forwarding errors, including:

a. The port receives packets that do not belong to the port's vlan, MAC errors, and unrecognized packets

b. Packets received in the non-forwarding state of the port (including stp discarding, learning, and Listening; lacp unselect; rrpp STANDBY)

c. Packets discarded by Layer 3 forwarding (direct connection without arp enters black hole and discards, routing black hole discards)

d. ACL restricts forwarded packets (such as rate limit drop, bandwidth suppression drop, broadcast suppression drop, ACL filtering)

e. The packet cannot find the outbound interface.

2. System special processing packet

a. The protocol packet is textually terminated and processed by the CPU (such as ospf packet, etc.)

b. TTL timeout packets, redirect packets and other local packets are not forwarded.

c. For internal protocol bandwidth restrictions, such as protocol packets such as stp, bandwidth guarantees and restrictions are made within the system.

d. Multicast processing packets

It can be seen that inDiscards actually reflects all the statistics of abnormally forwarded packets. Some packets are only marked as unable to be forwarded normally, but the packets are not actually discarded.

Therefore, the inDiscards node cannot be used as a node for judging link problems.

It is recommended that customers read the following ifInErrors node when judging link quality problems or forwarding packet loss.

.1.3.6.1.2.1.2.2.1.14

ifInErrors OBJECT-TYPE

  -- FROM       IF-MIB, RFC1213-MIB

  SYNTAX        Counter32

  MAX-ACCESS       read-only

  STATUS        current

  DESCRIPTION      "For packet-oriented interfaces, the number of inbound

            packets that contained errors preventing them from being

            deliverable to a higher-layer protocol.  For character-

            oriented or fixed-length interfaces, the number of inbound

            transmission units that contained errors preventing them

            from being deliverable to a higher-layer protocol.

            Discontinuities in the value of this counter can occur at

            re-initialization of the management system, and at other

            times as indicated by the value of

            ifCounterDiscontinuityTime."

::= { iso(1) org(3) dod(6) internet(1) mgmt(2) mib-2(1) interfaces(2) ifTable(2) ifEntry(1) 14 }

If it is the outbound direction, it is recommended to read the ifOutErrors node.

.1.3.6.1.2.1.2.2.1.20

ifOutErrors OBJECT-TYPE

  -- FROM       IF-MIB, RFC1213-MIB

  SYNTAX        Counter32

  MAX-ACCESS       read-only

  STATUS        current

  DESCRIPTION      "For packet-oriented interfaces, the number of outbound

            packets that could not be transmitted because of errors.

            For character-oriented or fixed-length interfaces, the

            number of outbound transmission units that could not be

            transmitted because of errors.

            Discontinuities in the value of this counter can occur at

            re-initialization of the management system, and at other

            times as indicated by the value of

            ifCounterDiscontinuityTime."

::= { iso(1) org(3) dod(6) internet(1) mgmt(2) mib-2(1) interfaces(2) ifTable(2) ifEntry(1) 20 }