MPLS, LDP, and RSVP

MPLS provides labelled forwarding for provider-style labs and VPNv4 scenarios. The engine covers label push, swap, pop, LDP-distributed labels, and BGP/MPLS VPN route projection.

Support level

Area	Level	Notes
MPLS dataplane	Supported	Label stack handling with push, swap, pop, and penultimate-hop popping.
LDP	Supported	Neighbour state and label mappings for IGP reachability.
LDP discovery	Supported	Link multicast Hello to 224.0.0.2 with TTL 1 plus active/passive session role.
VPN labels	Supported	VPNv4 routes carry label/RD/RT metadata.
LDP graceful restart	Supported	Stale binding mark/clear/purge behaviour during forwarding-holding window.
LDP TCP-MD5 password	Behaviour model	Symmetric password forms a session; asymmetric or mismatched password drops the session.
RSVP	Behaviour model	Handler surface exists; full RSVP-TE is not a support claim.
Provider cloud	Behaviour model	Black-box MPLS cloud can connect customer/provider-edge scenarios.

Standards coverage

Standard	Coverage	Notes
RFC 3031	Behaviour model	MPLS label stack forwarding.
RFC 3032 section 2.1.1	Supported	IPv4 explicit-null label 0 and implicit-null label 3 behaviour.
RFC 5036	Behaviour model	LDP neighbour and label mapping concepts.
RFC 3478	Behaviour model	LDP graceful restart stale-binding handling.
RFC 2385	Behaviour model	TCP-MD5-style LDP password match; no real TCP segment MAC.
RFC 4364	Behaviour model	BGP/MPLS IP VPN route separation.
RFC 3209	Minimal	RSVP-TE is not deeply implemented today.

Feature matrix

Feature	Status	Notes
MPLS interface enable	Supported	Marks interfaces for labelled forwarding.
Label push/swap/pop	Supported	Dataplane operations are represented.
PHP	Supported	Penultimate-hop pop behaviour.
LDP router ID	Supported	Identifies LDP speaker.
LDP neighbours	Supported	Discovered from enabled links.
Label bindings	Supported	Labels are allocated for routed FECs.
Multicast Hello	Supported	Link discovery uses 224.0.0.2 with TTL 1; MPLS-disabled interfaces drop it.
Active/passive TCP role	Supported	Passive LSR waits for Init; active LSR initiates.
Implicit null	Supported	Egress prefixes advertise label 3 by default.
Explicit null	Supported	Egress prefixes can advertise label 0 when configured.
LDP graceful restart	Supported	Peer bindings can be marked stale, cleared after recovery, or purged.
LDP neighbour password	Behaviour model	Passwords must match on both sides.
LDP notification	Behaviour model	Fatal notifications tear down the peer; non-fatal notifications are logged.
VPNv4 import/export	Supported	Driven by BGP route targets.
RSVP-TE tunnels	Not modelled	RSVP handler is not a full TE control plane.

Vendor command matrix

Command	IOS-style	Junos-style	VyOS-style	Notes
mpls ip	Supported	Partial	Partial	Interface MPLS enable.
mpls ldp router-id Loopback0 force	Supported	Partial	Partial	LDP identity.
mpls ldp explicit-null	Supported	Supported	Partial	Advertises IPv4 explicit-null label 0 for egress prefixes.
mpls ldp graceful-restart	Supported	Supported	Supported	Cisco, Junos, and VyOS config surfaces round-trip.
mpls ldp neighbor 2.2.2.2 password SECRET	Supported	Partial	Partial	TCP-MD5-style behaviour model.
show mpls forwarding-table	Supported	Partial	Partial	Label forwarding table.
show mpls ldp neighbor	Supported	Partial	Partial	LDP neighbour state.
show ldp neighbor	n/a	Supported	Partial	Junos operational show.
show ldp database	n/a	Supported	Partial	Junos operational show.
show ldp bindings	n/a	Supported	Partial	Junos operational show.
show bgp vpnv4 unicast all	Supported	Partial	Partial	VPNv4 routes.

Behaviour notes

MPLS forwarding is packet-oriented enough to test labelled reachability, while LDP remains a deterministic control-plane model. VPNv4 uses route distinguishers to keep overlapping customer prefixes separate and route targets to decide which VRFs import them.

LDP explicit-null is modelled at the label-binding boundary. Without explicit-null, an egress prefix advertises implicit-null label 3; with explicit-null, the same egress prefix advertises IPv4 explicit-null label 0.

LDP passwords model TCP-MD5 reachability semantics. If one side has a password and the other does not, or the values differ, the session does not form and the drop is observable in debug/syslog state.

Examples

Canonical example

configure terminal
interface GigabitEthernet0/0
 mpls ip
mpls ldp router-id Loopback0 force
end
show mpls ldp neighbor
show mpls forwarding-table

Vendor styles

IOS-style

mpls ip
mpls ldp router-id Loopback0 force
mpls ldp graceful-restart
mpls ldp explicit-null
interface GigabitEthernet0/0
 mpls ip

Junos-style

set protocols mpls interface ge-0/0/0.0
set protocols ldp interface ge-0/0/0.0
set protocols ldp transport-address 1.1.1.1
set protocols ldp graceful-restart
set protocols ldp explicit-null

VyOS-style

set protocols mpls interface eth0
set protocols ldp interface eth0
set protocols ldp discovery transport-ipv4-address 1.1.1.1
set protocols mpls ldp parameters graceful-restart

Known limits

RSVP-TE signalling, FRR bypass tunnels, real TCP-MD5 packet authentication, LDP ordered-vs-independent control nuance, and vendor-specific label allocation quirks are not fully modelled.