Label Distribution
Using Labels in Existing IP Routing Protocols
Implementing in DV routing protocols is very easy because each router's known prefixes come from its own routing table. The router only needs to bind the label to a prefix.
In the LS routing protocol, each router generates a link state update and transmits the update to all routers in the same area without modification. The problem is that if MPLS is to work properly, each router needs to distribute labels for each IGP prefix - even if a prefix does not originate from the router, which violates the working mode of the LS routing protocol and
uses independent label distribution. Protocol
Run an independent and dedicated protocol for label distribution—the advantage is that it does not affect the work of the routing protocol.
Distribution mode
Prerequisites for binding a label to a route prefix locally
Independent control mode
as long as the route is learned locally through IGP Prefix, a label will be assigned to this route prefix
(locally, a POP label will also be assigned to a directly connected route). In
orderly control mode
, the route prefix is learned locally through IGP, but the next hop router of the route prefix must be assigned to the prefix. The corresponding label mapping message is advertised to the local, and the local will assign the label to the prefix
Distribution mode
Downstream active mode DoD
will actively advertise the generated label mapping message to all LDP neighbors
. Downstream on-demand mode UD
Only when neighbor requests the local label mapping message for a certain prefix, the local will advertise the label mapping message to the neighbor
for reservation Mode
Free mode LLR
locally saves all label mapping information received from neighbors in the database
Conservative mode CLR
locally only saves the label mapping information of the route prefix advertised by the next hop neighbor of the optimal route
Label space is
based on the platform
locally advertised The label mapping information is globally meaningful, and the same label advertised from different interfaces corresponds to the same label
based on the interface