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SNMP counter
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This document explains the meaning of SNMP counters.
General IPv4 counters
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All layer 4 packets and ICMP packets will change these counters, but
these counters won't be changed by layer 2 packets (such as STP) or
ARP packets.
* IpInReceives
Defined in `RFC1213 ipInReceives`_
.. _RFC1213 ipInReceives: https://tools.ietf.org/html/rfc1213#page-26
The number of packets received by the IP layer. It gets increasing at the
beginning of ip_rcv function, always be updated together with
IpExtInOctets. It will be increased even if the packet is dropped
later (e.g. due to the IP header is invalid or the checksum is wrong
and so on). It indicates the number of aggregated segments after
GRO/LRO.
* IpInDelivers
Defined in `RFC1213 ipInDelivers`_
.. _RFC1213 ipInDelivers: https://tools.ietf.org/html/rfc1213#page-28
The number of packets delivers to the upper layer protocols. E.g. TCP, UDP,
ICMP and so on. If no one listens on a raw socket, only kernel
supported protocols will be delivered, if someone listens on the raw
socket, all valid IP packets will be delivered.
* IpOutRequests
Defined in `RFC1213 ipOutRequests`_
.. _RFC1213 ipOutRequests: https://tools.ietf.org/html/rfc1213#page-28
The number of packets sent via IP layer, for both single cast and
multicast packets, and would always be updated together with
IpExtOutOctets.
* IpExtInOctets and IpExtOutOctets
They are Linux kernel extensions, no RFC definitions. Please note,
RFC1213 indeed defines ifInOctets and ifOutOctets, but they
are different things. The ifInOctets and ifOutOctets include the MAC
layer header size but IpExtInOctets and IpExtOutOctets don't, they
only include the IP layer header and the IP layer data.
* IpExtInNoECTPkts, IpExtInECT1Pkts, IpExtInECT0Pkts, IpExtInCEPkts
They indicate the number of four kinds of ECN IP packets, please refer
`Explicit Congestion Notification`_ for more details.
.. _Explicit Congestion Notification: https://tools.ietf.org/html/rfc3168#page-6
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