Protocols and standards, Mpls configuration task list – H3C Technologies H3C S6800 Series Switches User Manual
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c.
Forwards the labeled packet out of the outgoing interface VLAN-interface 30 to the next hop
LSR Router D.
3.
When receiving the labeled packet, Router D (the egress) processes the packet as follows:
a.
Identifies the LFIB entry that has an incoming label of 50.
b.
Removes the label from the packet.
c.
Forwards the packet out of the outgoing interface VLAN-interface 40 to the next hop LSR Router
E.
If the LFIB entry records no outgoing interface or next hop information, Router D does the following:
d.
Identifies the FIB entry by the IP header.
e.
Forwards the packet according to the FIB entry.
PHP
An egress node must perform two forwarding table lookups to forward a packet:
•
Two LFIB lookups (if the packet has more than one label).
•
One LFIB lookup and one FIB lookup (if the packet has only one label).
The penultimate hop popping (PHP) feature can pop the label at the penultimate node, so the egress
node only performs one table lookup.
A PHP-capable egress node sends the penultimate node an implicit null label of 3. This label never
appears in the label stack of packets. If an incoming packet matches an LFIB entry comprising the implicit
null label, the penultimate node pops the top label of the packet and forwards the packet to the egress
LSR. The egress LSR directly forwards the packet.
Sometimes, the egress node must use the TC field in the label to perform QoS. To keep the TC information,
you can configure the egress node to send the penultimate node an explicit null label of 0. If an incoming
packet matches an LFIB entry comprising the explicit null label, the penultimate hop replaces the value of
the top label with value 0, and forwards the packet to the egress node. The egress node gets the TC
information, pops the label of the packet, and forwards the packet.
Protocols and standards
•
RFC 3031, Multiprotocol Label Switching Architecture
•
RFC 3032, MPLS Label Stack Encoding
•
RFC 5462, Multiprotocol Label Switching (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field
MPLS configuration task list
Tasks at a glance
(Optional.)
(Optional.)
Specifying the label type advertised by the egress
(Optional.)