Label Values; Figure 2 Label Packet Placement - Nokia 7705 SAR-W Series Manual

MPLS and RSVP-TE
A stack can carry several labels, organized in a last in/first out order. The top of the
label stack appears first in the packet and the bottom of the stack appears last
(Figure
Figure 2
The label value at the top of the stack is looked up when a labeled packet is received.
A successful lookup reveals:
In addition, the lookup may reveal outgoing data link encapsulation and other
information needed to properly forward the packet.
An empty label stack can be thought of as an unlabeled packet. An empty label stack
has zero (0) depth. The label at the bottom of the stack is referred to as the Level 1
label. The label above it (if it exists) is the Level 2 label, and so on. The label at the
top of the stack is referred to as the Level m label.
3.2.2.1
The 7705 SAR uses RSVP-TE and LDP protocols for label forwarding, For packet-
based services such as VLL, the 7705 SAR uses T-LDP for signaling PW labels
between peer nodes.
Packets traveling along an LSP are identified by the packet label, which is the 20-bit,
unsigned integer (see
1 048 575. Label values 0 to 15 are reserved and are defined below:
24
2).
Label Packet Placement
Top Labe l
Layer 2 Header
• the next hop where the packet is to be forwarded
• the operation to be performed on the label stack before forwarding

Label Values

Label Edge and Label Switch
• A value of 0 represents the IPv4 Explicit NULL label. This label value is legal only
at the bottom of the label stack if the label stack is immediately followed by an
IPv4 header, in which case the packet forwarding is based on the IPv4 header.
If the IPv4 Explicit NULL label is not at the bottom of the label stack, then the
packet forwarding is based on the subsequent label.
Use subject to Terms available at: www.nokia.com
. . .
Bottom Label
© 2022 Nokia.
MPLS Guide
Data Packet
19691
Routers). The range is 0 through
3HE 18686 AAAB TQZZA