vtp

package

v0.783.0 Latest Latest Go to latest Published: Jun 29, 2026 License: AGPL-3.0 Imports: 4 Imported by: 0

Details

Valid go.mod file
Redistributable license
Tagged version
Stable version
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Repository

github.com/xunholy/promptzero

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Documentation ¶

Overview ¶

Package vtp decodes Cisco's VLAN Trunking Protocol — the L2 protocol that synchronises the VLAN database across the switches of a VTP domain. VTP is a notorious switch-security hazard: a VTP server (or a rogue host that can reach a trunk) advertising a **higher configuration-revision number** overwrites the VLAN database of every switch in the domain — injecting a Subset advertisement with a high revision and an empty/forged VLAN list deletes or rewrites all VLANs domain-wide (a classic L2 denial-of-service). Decoding a captured VTP frame surfaces the domain name, the message type, and the all- important configuration revision — the reconnaissance a switch- security audit needs. It joins the project's switch / L2 decoders (internal/cdp, lldp, stp, lacp, vlan, macsec, dtp).

Wrap-vs-native judgement ¶

Native. A VTP PDU is a fixed header (version, code, a per-code
octet, a domain-name length + 32-octet domain name) followed by a
per-code body, carried in an LLC/SNAP frame (OUI 0x00000C, PID
0x2003). Decoding is byte-field extraction + a short record walk —
a dependency is not justified. stdlib only, no new go.mod dep.

Verifiable / no confidently-wrong output ¶

The header and the Summary / Subset bodies — including the VLAN
information records (id, name, status, type, MTU) of a Subset
advertisement — are decoded and were verified field-for-field
against scapy's VTP layer. The MD5 digest is surfaced as hex and
NOT verified (it is computed over the VLAN database + the VTP
password, which is not on the wire). Advertisement-Request and
Join messages carry little beyond the domain, so they are named
with the header decoded and the body left raw.

Index ¶

type Result
- func Decode(input string) (*Result, error)
type VLANInfo

Constants ¶

This section is empty.

Variables ¶

This section is empty.

Functions ¶

This section is empty.

Types ¶

type Result ¶

type Result struct {
	Version    int    `json:"version"`
	Code       int    `json:"code"`
	CodeName   string `json:"code_name"`
	DomainName string `json:"domain_name"`

	// Summary / Subset advertisement fields.
	Followers       *int   `json:"followers,omitempty"`        // Summary
	SequenceNumber  *int   `json:"sequence_number,omitempty"`  // Subset
	ConfigRevision  *int64 `json:"config_revision,omitempty"`  // the attack-critical field
	UpdaterIdentity string `json:"updater_identity,omitempty"` // Summary (IPv4)
	UpdateTimestamp string `json:"update_timestamp,omitempty"` // Summary (YYMMDDHHMMSS)
	MD5Hex          string `json:"md5_digest_hex,omitempty"`   // Summary (not verified)

	VLANs []VLANInfo `json:"vlans,omitempty"` // Subset advertisement

	PayloadHex string   `json:"payload_hex,omitempty"`
	Notes      []string `json:"notes,omitempty"`
}

Result is the decoded view of a VTP PDU.

func Decode ¶

func Decode(input string) (*Result, error)

Decode parses a VTP PDU. The input is hex (whitespace / ':' / '-' / '_' separators and a '0x' prefix tolerated). It may be the PDU itself, or any frame containing the LLC/SNAP VTP signature (OUI 0x00000C, PID 0x2003).

type VLANInfo ¶

type VLANInfo struct {
	VLANID     int    `json:"vlan_id"`
	Name       string `json:"name"`
	Status     int    `json:"status"`
	StatusName string `json:"status_name"`
	Type       int    `json:"type"`
	TypeName   string `json:"type_name"`
	MTU        int    `json:"mtu"`
}

VLANInfo is one VLAN record from a Subset advertisement.

Source Files ¶

View all Source files

decode.go

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