Basic Structure of tag Distribution Protocol LDP

In the introduction of MPLS, we should understand that it is a collection of multi-protocol combinations. One of them is the Label Distribution Protocol LDP, which is very important in MPLS technology and also a subject protocol. Now let's take a look at this agreement.

Label Distribution Protocol (LDP) is a major protocol in the MPLS system. In an MPLS network, two labels exchange router LSR) must be used between them or the labels that forward traffic through them to reach an agreement.

LDP defines a set of programs and messages. One LSR can notify another LSR of the tag bundle it has formed. Through the direct ing between the network layer routing information and the data link layer switching path, LSR can use the LDP protocol to establish the label switching path through the network.

Two label exchange routers (LSR) that use LDP to exchange label ing information are used as LDP peer nodes, and there is a LDP Label Distribution Protocol session between them. In a single session, each peer node can obtain other tag ing. In other words, this protocol is bidirectional.

Tag Distribution Protocol Structure

2 bytes	2 bytes
Version	PDU Length
LDP Identifier 6 bytes)
LDP Messages

Version-Protocol Version number. The current value is 1.

PDU Length-total PDU Length, excluding the version and PDU Length fields.

LDP Identifier-this field uniquely identifies the space where the LSR is sent by the PDU request. The starting 4 Octet encodes the IP address allocated to the LSR. The last 2 Octet indicates the tag space in the LSR.

LDP Messages-all

LDP Label Distribution Protocol information is in the following format:

U	Message Type	Message Length
Message ID
Parameters

U-U is an unknown bit.

Message type-information type. Information types include Notification, Hello, Initialization, Keep Alive, Address, Address Withdraw, Label Request, Label Withdraw, Label Release, and Unknown Message names.

Message Length-Information ID, command parameters, and optional parameters are eight characters long ).

Message ID-32-bit value, providing information recognition.

Parameters-Parameters include TLV. There are both command parameters and optional parameters. Some information does not have command parameters, and some information does not have optional parameters.

TLV format:

U	F	Type	Length
Value
TLV Format

U-U is an unknown TLV bit.

F-unknown TLV bit for forwarding.

Type-encode the Value field conversion.

Length-specifies that the Value field is eight characters long ).

Value: an eight-bit length string. The encoding length specified by the Type field.