Transport Mappings for version 2 of the Simple Network Management Protocol (SNMPv2)
obsoleted by
- rfc-1906 — Transport Mappings for Version 2 of the Simple Network Management Protocol (SNMPv2)
Extracted elements (26)
AppleTalk nodes lack stable network-layer addresses (DDP addresses can change at every reboot), so SNMPv2 over DDP uses NBP names as stable identifiers. A name-to-address cache with a configurable lifetime T1 (minimum 60 seconds) is used to minimize expensive NBP lookups and reduce CPU/network load.
UDP is the preferred transport mapping for SNMPv2. Systems deploying other mappings should also provide proxy service to the UDP mapping to ensure the greatest level of interoperability.
When a proxy relationship's destination party has rfc1157Domain as its transport domain, the proxy source party (contextSrcPartyIndex) and proxy context (contextProxyContext) are irrelevant; proxy agent behavior is governed by Section 3.1 of RFC 1452.
When NBP machinery is broken (e.g., FwdReq or BrRq failures at routers), a dedicated AppleTalk management entity may implement the router portion of NBP directly—sending NBP FwdReq and directed LkUp multicast datagrams—to recover name resolution for agents whose last known network address is known.
All AppleTalk nodes implementing the DDP mapping are required to respond to NBP lookups and confirms (i.e., implement the NBP protocol stub) to guarantee NBP-name-to-DDP-address resolution.
An SNMPv2 entity acting in an agent role must never prime its NBP cache; it should perform NBP lookups only when sending a trap, not when generating responses.
BER serialization must use only the definite form for length encoding; use of the indefinite form is prohibited. Using more than the minimum number of length octets in the definite-long form is permissible.
BER serialization must use the primitive encoding form for all simple ASN.1 types (INTEGER, OCTET STRING, OBJECT IDENTIFIER, BIT STRING); the constructed form must be used only for structured types (SEQUENCE or IMPLICIT SEQUENCE).
NBP type names for DDP agents must be 'SNMP Agent' and for notification sinks must be 'SNMP Trap Handler'; these names must be stored in stable storage and should not change more often than a typical TCP/IP node's IP address.
The maximum message size for the IPX mapping must be at least 546 octets; larger values are encouraged.
The maximum message size for the OSI mapping must be at least 484 octets; larger values are encouraged.
The maximum message size listed in partyTable for the UDP mapping must be at least 484 octets; implementation of larger values is encouraged.
When serializing a BIT STRING, all named-bits must be transferred regardless of their truth-value; if the number of named-bits is not an integral multiple of eight, zero-valued padding bits must be appended to reach the next octet boundary.
When setting partySecretsAuthPrivate for rfc1157noAuth, the exclusive-OR semantics specified in RFC 1447 still apply.
SNMPv2 over DDP uses DDP protocol type 8, agent socket number 8, and notification-sink socket number 9. Agents must register NBP type 'SNMP Agent'; notification sinks must register NBP type 'SNMP Trap Handler'.
SNMPv2 over IPX serializes each message onto a single IPX datagram using IPX packet type 4 (Packet Exchange). Agents should listen on IPX socket 36879 (0x900F); notification sinks on socket 36880 (0x9010).
SNMPv2 over OSI (CLTS) serializes each message onto a single TSDU. Agents using CL-mode service should listen on transport selector 'snmp-l'; notification sinks on 'snmpt-l'. For CO-mode, selectors are 'snmp-o' and 'snmpt-o' respectively.
SNMPv2 over UDP serializes each message onto a single UDP datagram using BER (Section 8). Agents should listen on UDP port 161; notification sinks should listen on UDP port 162.
The rfc1157Domain transport domain identifies proxy destinations for community-based SNMPv1 (RFC 1157). When partyTDomain is rfc1157Domain, partyTAddress must be 6 octets (4-octet IP address + 2-octet UDP port, network-byte order) and partyAuthProtocol must be rfc1157noAuth.
The rfc1157noAuth authentication protocol is used for SNMPv1 proxy. When active, partyAuthPublic, partyAuthClock, and partyAuthLifetime are irrelevant; partySecretsAuthPrivate is used as the SNMPv1 community string and must be at least one octet long (no maximum specified).
This document defines the SNMPv2-TM MIB module, assigning OIDs under snmpDomains for five transport domains: snmpUDPDomain ({snmpDomains 1}), snmpCLNSDomain ({snmpDomains 2}), snmpCONSDomain ({snmpDomains 3}), snmpDDPDomain ({snmpDomains 4}), and snmpIPXDomain ({snmpDomains 5}). It also assigns rfc1157Proxy ({snmpProxys 1}) with sub-OIDs rfc1157Domain and rfc1157noAuth.
Security issues are explicitly not discussed in this memo; the document defers all security considerations to other SNMPv2 framework documents.
SnmpIPXAddress is a fixed 12-octet OCTET STRING: octets 1–4 hold the network number, 5–10 hold the physical address, and 11–12 hold the socket number, all in network-byte order.
SnmpNBPAddress is a variable-length OCTET STRING (SIZE 3..99) encoding an NBP name with three length-prefixed fields: object (up to 32 octets), type (up to 32 octets), and zone (up to 32 octets); strings are case-insensitive and may contain any octet except 0xFF.
SnmpOSIAddress is a variable-length OCTET STRING (SIZE 1 or 4..85): octet 1 holds the NSAP length n (0 or 3–20), octets 2 through n+1 hold the NSAP in concrete binary, and remaining octets hold the TSEL (up to 64 octets).
SnmpUDPAddress is a 6-octet OCTET STRING: octets 1–4 carry the IP address in network-byte order, octets 5–6 carry the UDP port in network-byte order.