SNMPv2 Management Information Base for the Transmission Control Protocol using SMIv2
obsoleted by
- rfc-4022 — Management Information Base for the Transmission Control Protocol (TCP)
updates
- rfc-1213 — Management Information Base for Network Management of TCP/IP-based internets: MIB-II
Extracted elements (19)
The TCP MIB module supports only IPv4: all address fields use the IpAddress type (OCTET STRING of length 4) and do not accommodate 128-bit IPv6 addresses, as noted in the IESG Note.
This document updates RFC 1213 (MIB-II) by redefining the same TCP managed objects using the SNMPv2 SMIv2 framework (RFC 1902) rather than the original SNMPv1 framework.
The only value a management station may set on tcpConnState is deleteTCB(12); an agent MUST return a 'badValue' response if any other value is attempted.
Setting tcpConnState to deleteTCB(12) causes the agent to delete the TCP Control Block (TCB) of that connection, resulting in immediate termination; as an implementation-specific option the agent may send a RST segment to the remote endpoint.
tcpActiveOpens (OID tcp 5) is a Counter32 counting direct transitions from CLOSED to SYN-SENT; tcpPassiveOpens (tcp 6) counts direct transitions from LISTEN to SYN-RCVD.
tcpAttemptFails (OID tcp 7) counts transitions to CLOSED from SYN-SENT or SYN-RCVD, plus transitions to LISTEN from SYN-RCVD, capturing connection-establishment failures.
tcpConnLocalAddress and tcpConnRemAddress are IpAddress (4-octet IPv4) fields; for a listening connection willing to accept on any interface, tcpConnLocalAddress carries 0.0.0.0.
tcpConnTable (OID tcp 13) is a conceptual table of current TCP connections, indexed by tcpConnLocalAddress, tcpConnLocalPort, tcpConnRemAddress, and tcpConnRemPort; each row is transient and ceases to exist when the connection reaches CLOSED.
tcpCurrEstab (OID tcp 9) is a Gauge32 reflecting the instantaneous number of TCP connections in the ESTABLISHED or CLOSE-WAIT state.
tcpEstabResets (OID tcp 8) is a Counter32 counting transitions to CLOSED from ESTABLISHED or CLOSE-WAIT, representing connections that were reset after being fully established.
tcpInErrs (OID tcp 14) is a Counter32 of segments received in error (e.g., bad TCP checksums); tcpOutRsts (tcp 15) counts TCP segments sent containing the RST flag.
tcpInSegs (tcp 10) counts all received segments including those in error; tcpOutSegs (tcp 11) counts sent segments excluding retransmit-only segments; tcpRetransSegs (tcp 12) counts segments containing at least one previously transmitted octet.
tcpMaxConn (OID tcp 4) is a read-only Integer32 expressing the maximum number of TCP connections the entity can support; the value -1 is used when the maximum is dynamic.
tcpRtoAlgorithm (OID tcp 1) is a read-only INTEGER indicating the retransmission timeout algorithm in use: other(1), constant(2), rsre(3) (MIL-STD-1778), or vanj(4) (Van Jacobson's algorithm).
tcpRtoMin and tcpRtoMax (OIDs tcp 2 and tcp 3) are read-only Integer32 objects in milliseconds giving the minimum and maximum retransmission timeout values permitted by the TCP implementation; for the rsre algorithm they correspond to LBOUND and UBOUND from RFC 793.
The TCP MIB module (tcpMIB) is assigned OID { mib-2 49 } and defines the managed objects for TCP implementations, migrating the TCP group from MIB-II (RFC 1213) to the SNMPv2 SMIv2 framework.
The conformance group tcpGroup (OID tcpMIBGroups 1) mandates all 19 TCP MIB objects as a single OBJECT-GROUP; tcpMIBCompliance declares tcpGroup as the sole MANDATORY-GROUP for SNMPv2 entities implementing TCP.
The RFC explicitly states that security issues are not discussed in this memo, providing no guidance on access control or authentication for the TCP MIB objects, including the writable tcpConnState object that can forcibly terminate connections.
tcpConnState enumerates all eleven standard TCP states—closed(1), listen(2), synSent(3), synReceived(4), established(5), finWait1(6), finWait2(7), closeWait(8), lastAck(9), closing(10), timeWait(11)—plus the management action deleteTCB(12) which forces immediate connection termination.