MPLS label mode/distribution behavior/retention mode/Label Space

MPLS label mode/distribution behavior/retention mode/Label Space
LDP uses the independent distribution mode, Active distribution, and free-reserve mode. the tag space is platform-based, that is, each platform distributes a tag (instead of an interface-based) for the prefix. These configurations are fixed working modes and cannot be modified in LDP. --- Allocation mode: the prerequisite for binding a Label to a route prefix locally in Label Allocation. butler independent Control mode: Idenpendent Control here, there is A network, connected to R3, is R3 direct connection. r3 will assign a pop to A because it is A direct connection. when R2 learns A through IGP, it will assign A non-empty tag 201 to A without any order. It does not mean that it must wait until R3 has been assigned the tag, and R2 will be allocated after receiving it. They all work independently. If a pharmaceutical company has an IGP route, tags will be assigned to it. the same is true for R1, where 101 labels are assigned to the network learned by IGP. summary: as long as the route prefix learned locally through IGP, a label is assigned to each route prefix, and a POP label is assigned to the local route. Note, the POP tag must be a local direct connection, and no empty tag will be assigned for non-direct connections. when tags are assigned, there is no sequence and no logic relationship. As long as there is an IGP route locally, there is no label for direct connection, and non-direct connection routes are allocated with normal working labels. Ordered Control mode: Odered Control mode. In this mode, the upstream router must be assigned a label to the local router to assign a label to the IGP route. There is an order in it. That is to say, the next hop router with the route prefix must advertise the tag ing message corresponding to the prefix to the local machine to assign tags to the prefix. All actions are ordered. r3 first assigns a pop empty tag to network. then R3 is assigned to R2. After receiving the label assigned by the upstream router, R2 allocates 201 to network. netwotrk A will be assigned A 101 tag only after R1 receives it. -- Distribution mode: Label Distribution-Downstream active mode: Downstream Unsolicited (LDP uses Downstream active mode by default) meaning: the generated tag ing message is automatically advertised to all LDP neighbors. that is to say, as long as the local router generates a label, no matter whether you are upstream or downstream, I will take the initiative to distribute the label to you. as shown in the figure, R2 assigns A 201 tag for the IGP route Prefix A, and then R2 distributes tags for all LDP neighbors. -listener-Downstream on-Demand mode: Downstream on Demand mode meaning: only when a neighbor requests a tag ing message with a specified prefix to the local device will the local device advertise the tag ing message to the neighbor. we can see that R1 is the downstream router and the request tag is n. Etwork A sends to R2, R2 sends to R3 (request), R3 responds to the label of R2 network A, then R2 will respond to the request of R1 label. all labels are distributed as needed. -- Retention mode: Label Retention mode: whether the local database retains all tag ing messages received from neighbors. -Free mode: Liberal Retention (LDP mode) Any LDP neighbor gives me a local tag, which must exist in the local tag database. if there are two next-hop IGP routes that can reach the peer end, no matter whether it is Server Load balancer or not, as long as it is the label assigned to me by the LDP neighbor, I will save it to the local tag database. advantage: with the backup label, the master FEC can be quickly switched to the slave label for data forwarding if it is down. disadvantage: occupying more tag space. -Keep-conservative mode: Liberal Retention only stores the tag ing message of the route prefix advertised by the next hop neighbor of the Optimal Route locally. it means that you are my next hop, give me the tag, and save it. If you are not my next hop in the core route table, I will lose the label you gave me. Here, A directly connected network (network A. R2 and R4) after R3 will distribute the label information to R1. However, R1 will query the IGP core route table, who is the best next hop. In the figure, R2 is the next hop. Therefore, R1 stores the labels distributed by R2, And the labels distributed by R4 are discarded. advantage: saves tag space. disadvantage: after the main line is down, there is no backup label as a backup. -- Label Space: Label Space. Each time you view show mpls ldp neighbor, you can see a number next to the ldp id. always 0. this is the tag space. label space: Label space ----- whether all the labels advertised locally are meaningful to the local (Interface) or globally. ◆ platform-based: Per-Platfrom, frame mode, that is, the Local ldp id is followed by 0. explanation: that is to say, R2 assigns A label to the network A prefix, And it will distribute the label to all neighbors. all the neighbors receive the same tag. ◆ Interface-based: Per-Interface, used in cell source mode. then you can stay on the concept. R2 assigns A tag to the prefix of network A and 201 to R1. assigns 202 to R4. assigns tags Based on interfaces. The "tag behavior" CELL protocol of the source protocol uses the following: the tag allocation mode is the ordered control mode, the tag distribution mode is the downstream on-demand mode, and the tag retention mode is the conservative mode, only the labels distributed by the optimal IGP path are saved. For other packet loss tags, the tag space is based on the Interface (Per-Interface)