The MPLS header is of 32 bits. It contains the following information:-
1. Label: The label field is of 20 bits.
2. Experimental(Exp):The three bits are reserved as experimental bits. They are used for Quality of Service(QoS).
3. Bottom of Stack(BoS): A network packet can have more than one MPLS labels which are stacked one over another. To ensure which MPLS label is at the bottom of stack we have a BoS field which is of 1 bit.
4. Time to Live(TTL): The last 8 bits are used for Time to Live(TTL).
For the MPLS domain to forward traffic, a label stack is required. Specifically, two labels are required for traffic to be successfully forwarded through the MPLS domain. The first label that is attached to the packet is a VPN label, and the second label that is attached is the LDP label.
Multiprotocol Label Switching (MPLS) is a protocol for speeding up and shaping network traffic flows. MPLS allows most packets to be forwarded at Layer 2 (the switching level) rather than having to be passed up to Layer 3 (the routing level). Each packet gets labeled on entry into the service provider's network by the ingress router. All the subsequent routing switches perform packet forwarding based only on those labels - they never look as far as the IP header. Finally, the egress router removes the label(s) and forwards the original IP packet toward its final destination.
The Dynamic Multipoint VPN (DMVPN) feature allows users to better scale large and small IPSec VPNs by combining generic routing encapsulation (GRE) tunnels, IPSec encryption, and Next Hop Resolution Protocol (NHRP) to provide users with easy configuration through crypto profiles, which override the requirement for defining static crypto maps, and dynamic discovery of tunnel endpoints.
DMVPN (Dynamic Multipoint VPN) is a routing technique that can be used to build a VPN network with multiple sites without having to statically configure all devices. It's a "hub and spoke" network where the spokes will be able to communicate with each other directly without having to go through the hub. Encryption is supported through IPsec which makes DMVPN a popular choice for connecting different sites using regular Internet connections.