UnderlyingSecurityIDSource (FIX tag 305)

StringFIX 4.4FIX 4.2FIX 5.0 SP2

UnderlyingSecurityIDSource (tag 305) is a String field defined in FIX 4.4, FIX 4.2 and FIX 5.0 SP2. It appears in 59 message types, always optionally. FIX 4.2 calls this field UnderlyingIDSource; the tag number is unchanged, so the two are the same field on the wire.

Also known as UnderlyingIDSource

FIX 4.2 calls tag 305 UnderlyingIDSource. It is the same field on the wire — only the name changed — so a message encoded by either side interoperates.

At a glance

Tag: 305
Name: UnderlyingSecurityIDSource
Datatype: String
Dialects: FIX 4.4, FIX 4.2 and FIX 5.0 SP2
Messages: 59

What the specification says

FIX 4.4

Underlying security’s SecurityIDSource. Valid values: see SecurityIDSource (22) field

FIX 4.2

Underlying security’s IDSource.

FIX 5.0 SP2

Identifies class or source of the UnderlyingSecurityID(309) value.

Descriptions are quoted from the FIX Orchestra sources under the Apache 2.0 licence.

A real message using tag 305

NewOrderSingle · FIX 4.4

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.4
9	BodyLength	165
35	MsgType	D	Order – Single
49	SenderCompID	BOARTEAM
56	TargetCompID	COUNTERPARTY
34	MsgSeqNum	2
52	SendingTime	20240101-12:00:00.000
11	ClOrdID	ORD-10042
711	NoUnderlyings2 entries	2	repeating group
311	UnderlyingSymbol	EXAMPLE
305	UnderlyingSecurityIDSource	EXAMPLE
311	UnderlyingSymbol	EXAMPLE
305	UnderlyingSecurityIDSource	EXAMPLE
54	Side	1	Buy
60	TransactTime	20240101-12:00:00.000
40	OrdType	1	Market
10	CheckSum	132

Edit and decode it yourself

Shown with | separators for readability. On the wire FIX uses SOH (0x01), an invisible control byte — and because BodyLength and CheckSum are computed over the actual bytes, the two forms have different checksums. Both are valid and both decode here.

Open in the full decoder →

Generated from the FIX 4.4 dictionary and verified at build time: it parses and validates with no issues. Open the decoder to try your own message.

Where tag 305 appears

Requiredness is a property of the message, not of the field: the same tag can be optional in one message and conditionally required in another.

Message	MsgType	FIX 4.4	FIX 4.2	FIX 5.0 SP2	Where in the message
Advertisement	7	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
AllocationInstruction	J	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
AllocationInstructionAlert	BM	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
AllocationReport	AS	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
AssignmentReport	AW	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CollateralAssignment	AY	Optional	—	Optional	inside UndInstrmtCollGrp › UnderlyingInstrument
CollateralInquiry	BB	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CollateralInquiryAck	BG	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CollateralReport	BA	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CollateralRequest	AX	Optional	—	Optional	inside UndInstrmtCollGrp › UnderlyingInstrument
CollateralResponse	AZ	Optional	—	Optional	inside UndInstrmtCollGrp › UnderlyingInstrument
Confirmation	AK	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
ContraryIntentionReport	BO	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CrossOrderCancelReplaceRequest	t	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
CrossOrderCancelRequest	u	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
DerivativeSecurityList	AA	Optional	—	Optional	inside the UnderlyingInstrument component
DerivativeSecurityListRequest	z	Optional	—	Optional	inside the UnderlyingInstrument component
DerivativeSecurityListUpdateReport	BR	—	—	Optional	inside the UnderlyingInstrument component
DontKnowTrade	Q	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
Email	C	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
ExecutionAcknowledgement	BN	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
ExecutionReport	8	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
IOI	6	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
ListStrikePrice	m	Optional	—	Optional	inside UndInstrmtStrkPxGrp › UnderlyingInstrument
MarketDataIncrementalRefresh	X	Optional	—	Optional	inside MDIncGrp › UndInstrmtGrp › UnderlyingInstrument
MarketDataRequest	V	Optional	—	Optional	inside InstrmtMDReqGrp › UndInstrmtGrp › UnderlyingInstrument
MarketDataSnapshotFullRefresh	W	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
MassQuote	i	Optional	Optional	Optional	inside QuotSetGrp › UnderlyingInstrument
MassQuoteAcknowledgement	b	Optional	Optional	Optional	inside QuotSetAckGrp › UnderlyingInstrument
MultilegOrderCancelReplace	AC	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
NewOrderCross	s	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
NewOrderList	E	Optional	—	Optional	inside ListOrdGrp › UndInstrmtGrp › UnderlyingInstrument
NewOrderMultileg	AB	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
NewOrderSingle	D	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
News	B	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
OrderCancelReplaceRequest	G	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
OrderCancelRequest	F	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
OrderMassActionReport	BZ	—	—	Optional	inside the UnderlyingInstrument component
OrderMassActionRequest	CA	—	—	Optional	inside the UnderlyingInstrument component
OrderMassCancelReport	r	Optional	—	Optional	inside the UnderlyingInstrument component
OrderMassCancelRequest	q	Optional	—	Optional	inside the UnderlyingInstrument component
OrderMassStatusRequest	AF	Optional	—	Optional	inside the UnderlyingInstrument component
OrderStatusRequest	H	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
PositionMaintenanceReport	AM	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
PositionMaintenanceRequest	AL	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
PositionReport	AP	Optional	—	Optional	inside PosUndInstrmtGrp › UnderlyingInstrument
Quote	S	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
QuoteCancel	Z	Optional	—	Optional	inside QuotCxlEntriesGrp › UndInstrmtGrp › UnderlyingInstrument
QuoteRequest	R	Optional	—	Optional	inside QuotReqGrp › UndInstrmtGrp › UnderlyingInstrument
QuoteRequestReject	AG	Optional	—	Optional	inside QuotReqRjctGrp › UndInstrmtGrp › UnderlyingInstrument
QuoteResponse	AJ	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
QuoteStatusReport	AI	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
QuoteStatusRequest	a	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
RFQRequest	AH	Optional	—	Optional	inside RFQReqGrp › UndInstrmtGrp › UnderlyingInstrument
RequestForPositions	AN	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
RequestForPositionsAck	AO	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityDefinition	d	Optional	Optional	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityDefinitionRequest	c	Optional	Optional	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityDefinitionUpdateReport	BP	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityList	y	Optional	—	Optional	inside SecListGrp › UndInstrmtGrp › UnderlyingInstrument
SecurityListRequest	x	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityListUpdateReport	BK	—	—	Optional	inside SecLstUpdRelSymGrp › UndInstrmtGrp › UnderlyingInstrument
SecurityStatus	f	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
SecurityStatusRequest	e	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
TradeCaptureReport	AE	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
TradeCaptureReportAck	AR	—	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
TradeCaptureReportRequest	AD	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument
TradeCaptureReportRequestAck	AQ	Optional	—	Optional	inside UndInstrmtGrp › UnderlyingInstrument

Wire format

Free-form text. Any byte except the SOH separator is legal, so values are not trimmed or case-folded on the wire. @boarteam/fix keeps the value as a string; format rules are checked by validate(), which reports validate/invalid-value rather than throwing.

Read tag 305 in TypeScript

decode.tsts

import { createFixEngine } from "@boarteam/fix";import { dictionary } from "@boarteam/fix-dict-fix44";const fix = createFixEngine(dictionary);const { message, issues } = fix.parse(raw);const field = message.fields[305];field?.name;   // "UnderlyingSecurityIDSource"field?.raw;    // the verbatim wire stringfield?.value;  // coerced to a string

Decode this in your own code

The same engine that produced the decoded example above is an Apache-2.0 npm package with zero runtime dependencies. It runs in Node and in the browser, and parse() returns problems as data instead of throwing.

npm i @boarteam/fix @boarteam/fix-dict-fix44

Try the decoder Source on GitHub