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MPLS — Label Switching

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Plain IP packet (pre-MPLS)Layer 3 · NetworkIPv4

Src

192.168.1.10

Dst

192.168.2.20

Plain IP packet (pre-MPLS)Layer 3 · NetworkIPv4

Src

192.168.1.10

Dst

192.168.2.20

MPLS: labels instead of IP lookups

MPLS (Multiprotocol Label Switching) was designed when IP longest-prefix-match lookups were too slow for high-speed backbone links. Labels are short fixed-length integers — lookup is a hash table O(1) operation, not a trie walk.

Today, hardware can do IP lookups at line rate, but MPLS remains essential for traffic engineering and VPN services (L3VPN, pseudowires).

Plain IP packet (pre-MPLS)TCP

Packet structure

Payload

L3

Layer details (click to expand)

3

NetworkIPv4

▼

Packets in motion — click to inspect:

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