---
title: Logon
seo:
  title: Logon | FIX Session
  description: "FIX session Logon reference: field layout, repeating groups,
    supported values, and message-specific behavior."
sidebar:
  label: Logon
---
`MsgType(35)=Logon(A)`

Direction: **Both directions**.

Establish the FIX session and its application protocol version.

## Field Layout

See [FIX Message Layouts](/reference/fix-message-layouts) for field ordering and presence rules.

| Field | Type | Presence | Behavior |
| --- | --- | --- | --- |
| `EncryptMethod(98)` | [`INT`](/reference/fix-data-types#int) | Required |  |
| `HeartBtInt(108)` | [`INT`](/reference/fix-data-types#int) | Required | <span style="overflow-wrap:anywhere">Heartbeat interval in seconds. Must be at least 30 seconds. A Logon(A) request with a shorter interval is answered with Logout(5), and the connection is closed.</span> |
| `ResetSeqNumFlag(141)` | [`BOOLEAN`](/reference/fix-data-types#boolean) | Optional |  |
| `DefaultApplVerID(1137)` | [`STRING`](/reference/fix-data-types#string) | Required |  |