
4
Figure 4 Process of dynamic LSP establishment
Label distribution and management
An LSR informs its upstream LSRs of labels assigned to FECs through label advertisement. The
label advertisement modes include downstream unsolicited (DU) and downstream on demand (DoD).
The label distribution control modes include independent and ordered.
Label management specifies the mode for processing a received label binding that is not useful at
the moment. The processing mode, called "label retention mode," can be either liberal or
conservative.
Figure 5 Label advertisement modes
As shown in
, the label advertisement modes include the DU mode and the DoD mode.
•
In DU mode, an LSR assigns a label to a FEC and then distributes the FEC-label binding to its
upstream LSR without solicitation. The device supports only the DU mode.
•
In DoD mode, an LSR assigns a label to a FEC and distributes the FEC-label binding to its
upstream LSR only when it receives a label request from the upstream LSR.
To establish an LSP, an upstream LSR and its downstream LSR must use the same label
advertisement mode.
Label distribution control modes include the independent mode and the ordered mode.
LSR A
LSR B
LSR D
LSR C
LSR E
LSR F
LSR G
LSR H
Ingress
Egress
LSP
Label mapping
Egress
Transit
DU mode
DoD mode
2) Send a label request for the
FEC to the downstream.
3) Distribute a label mapping for
the FEC to the upstream upon
receiving the request.
Ingress
1) Unsolicitely distribute a label
mapping for a FEC to the upstream.
1) Send a label request for a FEC
to the downstream.
2) Unsolicitely distribute a label
mapping for the FEC to the
upstream.
4) Distribute a label mapping for
the FEC to the upstream upon
receiving the request.