Label Distribution And Control - HP FlexNetwork 10500 Series Configuration Manual

Establishing LSPs
LDP classifies FECs according to destination IP addresses in IP routing entries, creates FEC-label
mappings, and advertises the mappings to LDP peers through LDP sessions. After an LDP peer
receives an FEC-label mapping, it uses the received label and the label locally assigned to that FEC
to create an LFIB entry for that FEC. When all LSRs (from the Ingress to the Egress) establish an
LFIB entry for the FEC, an LSP is established exclusively for the FEC.
Figure 9 Dynamically establishing an LSP
Ingress
LSR A
LSR E

Label distribution and control

Label advertisement modes
LDP advertises label-FEC mappings in one of the following ways:
•
Downstream Unsolicited (DU) mode—Distributes FEC-label mappings to the upstream LSR,
without waiting for label requests. The device supports only the DU mode.
•
Downstream on Demand (DoD) mode—Sends a label request for an FEC to the downstream
LSR. After receiving the label request, the downstream LSR distributes the FEC-label mapping
for that FEC to the upstream LSR.
Figure 10 Label advertisement modes
DU mode
DoD mode
LSR B
LSR F
2) Unsolicitedly distributes a label
mapping for the FEC to the
upstream.
Ingress
1) Sends a label request for a
FEC to the downstream.
4) Distributes a label mapping for
the FEC to the upstream upon
receiving the request.
Egress
LSR C
LSR D
LSR G
LSR H
1) Unsolicitedly distributes a label
mapping for a FEC to the
upstream.
Transit
2) Sends a label request for the
FEC to the downstream.
3) Distributes a label mapping for
the FEC to the upstream upon
receiving the request.
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Label mapping
LSP
Egress