IT Certification

Operation of the label are: label distribution, label mapping, clear labels, label distribution, label to maintain, as label converting and label the merger

1.1 label binding and mapping: The forward equivalence class labels f and l for binding, is done by the downstream lsr decision, and the upper reaches of the binding notice to the lsr. Map divided into two categories: one is the router at the entrance to the label map, a map of the region is mpls. In the first mapping, the router is the entrance into the business stream, the separation of multiple fec, then tag and its binding; lsr another input is mapped to a series of fec label, and then under the map the packet transmitted along the channel.
1.2 Assignment Tags: mpls label switching is the nature of network layer routing and data link layer to bind the label and label binding information in label switching forwarding between routers, the process is also known as label assignment. Common label assignment has a topology-based business-driven control; b based on the volume of requests for control of the business-driven; c data-driven business.

The first one is the label assignment corresponds to the normal routing protocols to deal with control of the business, when dealing with lsr or ospf routing bgp update, on the one hand, to modify their entries published, on the one hand, the distribution of these entries corresponding to the label. As long as there is a routing, network label on the completed assignment in advance, so that when there is no label forward the establishment of latency.

The second is the tag assignment request based on the control of the normal volume of business to deal with the corresponding, corresponding to the agreement he is rsvp, when lsr when dealing with rsvp, on the one hand, to modify their entries published, on the one hand, the distribution of labels for these entries . This program requires pre-application request for the use of labeling and flow specifications in order to obtain labels, it is also in accordance with pre-existing routing label to complete the assignment, there is no label to establish latency.

The third is a data-driven business. Lsr data flow to reach the “trigger” label assignment and label distribution. In this scenario, label assignment and distribution of overhead traffic is a function of direct proportion, there is value associated with the labeling delay, if you want a particular label assigned to specific network resources to support a particular network program on the need to use data-driven approach.

Compared with the data-driven, control of the business-driven label assignment has several advantages: 1) label assignment and distribution of information therefore corresponds to the control of the network will not lead to large expenses, 2) prior to arrival in the data and the establishment of label assignment distribution, are not labeled the establishment of latency,
Lsr label refers to the recovery of the label will be useless for recycling in order to re-assignment. Generally speaking, when the assignment of a label is no longer the establishment of the conditions, on their recovery.

1.3 Packaging and Labeling of coding labels
1.3.1 the use of dedicated hardware and software mpls forwarding label division at the data link layer and network layer of the middle layer of “pads” package pads to the network layer, but independent of the network layer protocol, so can be packaged in any of the network layer packet, in this way become a “general mpls package.”

Any type of network layer packet

Any type of network layer packet Mpls gasket

Any type of network layer packet data link layer Mpls header gasket

1.3.2 Based on atm switch mpls label package, atm switch using input port and input vci / vpi as cross-connect table to find the index, exterior access from the cross-connect output ports and output vci / vpi, in order to complete the exchange. If the adoption of appropriate ways of encoding one or more tags Add vci / vpi region can be modified for atm switch atm-lsr. There are three ways to say that the label incorporated into the cell in: 1) SVC coding. With vci / vpi domain of the label in the Top-encoded, the lsp as svp, will be seen as ldp signaling protocols atm, but can not atm-lsr label stack to stack operations push and shells; 2) SVP coding. VPI domain used for encoding of the Top-label, if there is a second label layer stack labels, VCI used on the second level domain encoded tags, such a program than before the advantages of a program is to support the exchange of atm’s vp. 3) svp multi-point code. VPI domain with the same label on the Top-encoded, using the domain part of VCI on the second tier label encoded with VCI domain specified in other parts of the entrance to lsp logo. Such programs can support multi-point-to-point atm switch the vp.

1.4 Label Distribution
In the use of labels before lsr between the two labels must be on understanding the use of consensus, this process is called label distribution, or can be understood as a lsr a lsr to notice it’s on the label and a binding fec series of the sum of the process.
1.4.1 Label Distribution manner. According to label the different distribution of the main body can be divided into upstream and downstream label distribution label distribution, currently used by downstream label distribution, it can be divided into two types: 1) downstream-on-demand distribution; 2) the distribution of the lower reaches of the initiative. The former is a kind of upstream LSR for a FEC label to the downstream LSR to the distribution of applications, the latter is the downstream LSR to the upstream LSR label bound to inform the relevant information, regardless of whether the upstream LSR to apply to him. Distribution of these two labels can be found in the same network, but any case, the downstream LSR must be adopted prior to the label distribution agreement. In fact, the distribution of the process of labeling is to establish some kind of FEC LSP LSP process. Label Distribution Control Mode, there are two: an independent label control mode and in an orderly pattern of the label control.

1.4.2 Label Distribution channels. LSR label distribution peers, can be used mpls specialized ldp agreement provided for the distribution, you can carry the label in the other routing protocols on the transfer, the former referred to as explicit label distribution, the distribution of the latter into a label implied.
Explicit Label Distribution 1.4.2.1. Show label distribution mode, the label distribution protocol in the topology-driven and business-driven approach to work under two types of trigger, label distribution protocol ldp to determine two issues: 1) two ldp between peers who provided the label forwarding ; 2) the establishment of LSP label should be the path forward point from which to start. Answer the second question first, you can export from the entrance to the establishment of the path can also be exported to the entrance of the establishment of the path. The first question can be from the downstream label distribution, but also by the upstream label allocation, if the downstream LSR, label distribution, it works in this way the LSR of the label for the exchange of index table, if carried out by the upstream LSR label distribution, it works in this way the LSR for the exchange of the label to find the results table.

1.5 label removal
Clear labeling for two reasons: 1) mpls label space is limited, so the label must be removed after use for recycling, the other for the use of the information carrier, 2) due to changes in network topology resulting in the disappearance of the reasons for the existence of labels, that is, the routing tag corresponding to non-existent or ineffective. There are clear mechanisms for the following labels: 1) the use of time to clear the way labels; 2) the use of peer mpls activation mechanism to maintain a clear label.

1.6 tags to keep
If the LSR a separate body from the three pairs, such as b, c, d received a tag on the same destination, but only in accordance with routing protocols to send the label c to be effective, a label for the other two on how to handle it If a continued preservation of these two labels, then once when b or d to the final destination to become effective when the next hop, a direct use of these labels, do not have to re-apply, in this way to maintain a free model, if a discarded out of these two labels, then when b or d to reach the final destination to become effective when the next hop, but also re-issued to the b or d labeling applications to maintain this way as a conservative mode. To maintain the conservative mode, labels can save space, while preserving the label forwarding table is also relatively small, save resources, it is general and the lower reaches of the way on-demand label distribution with the work mode for the freedom to maintain a relatively strong ability to adapt to the routing, but increase the system burden, general and downstream label distribution with independent work.