VPLS allows remote sites to share an Ethernet broadcast domain by connecting sites through pseudo-wires (PW) tunnels over a packet switching network (PSN). Since VPLS encapsulation adds additional overhead, each interface in the LSP should be able to transmit a large enough packet.
When the MPLS label is attached to the packet, it increases the packet length by 32 bits (4 bytes). These 32 bits are broken down as follows:
MikroTik RouterOS implements Label Distribution Protocol (RFC 3036, RFC 5036, and RFC 7552) for IPv4 and IPv6 address families. LDP is a protocol that performs the set of procedures and exchanges messages by which Label Switched Routers (LSRs) establish Label Switched Paths (LSPs) through a network by mapping network-layer routing information directly to data-link layer switched paths.
MPLS stands for MultiProtocol Label Switching. Instead of using IP routing, MPLS bases the packet forwarding decision (outgoing interface and next-hop router) on labels attached to a packet, rather than on fields in the IP header (such as destination address) and the routing table. This approach speeds up the forwarding process because the next-hop lookup is simpler than routing lookup (finding the longest matching prefix).