Control Word; Pw Redundancy - HP FlexNetwork 10500 Series Configuration Manual

configure flexible match criteria for the Ethernet service instance. For example, configure the
Ethernet service instance to match all packets, tagged packets, or untagged packets. The
default PW type for flexible mode is VLAN. Flexible mode can also implement the port and
VLAN modes through match criteria configuration.

Control word

The control word field is between the MPLS label stack and the Layer 2 data. It carries control
information for the Layer 2 frame, for example, the sequence number.
The control word feature has the following functions:
•
Avoids fragment disorder. In multipath forwarding, fragments received might be disordered. The
control word feature reorders the fragments according to the sequence number carried in the
control word field.
•
Identifies the original payload length for packets that include padding.
When the PW type is Ethernet or VLAN, the control word field is optional. You can configure whether
to carry the control word field in packets sent on the PW. If you enable the control word feature on
both PEs, packets transmitted on the PW carry the control word field. Otherwise, the packets do not
carry the control word field.

PW redundancy

PW redundancy provides redundant links between PEs so that the customer networks can
communicate when the path over one PW fails. As shown in
(one primary and one backup). The CEs communicate through the primary PW. When the primary
PW fails, PE 1 brings up the backup PW and forwards packets from CE 1 to CE 2 through the backup
PW. When CE 2 receives the packets, it updates its MAC address table, so that packets from CE 2 to
CE 1 also travel through the backup PW. Only static PWs and LDP PWs support PW redundancy.
Figure 86 PW redundancy
CE 1
The MPLS L2VPN determines whether the primary PW fails according to the LDP session status or
the BFD result. The backup PW is used when one of the following conditions exists:
•
The public tunnel of the primary PW is deleted, or BFD detects that the public tunnel has failed.
•
The primary PW is deleted because the LDP session between PEs goes down, or BFD detects
that the primary PW has failed.
•
A manual PW switchover is performed.
MPLS or IP backbone
PE 2
PE 1
PE 3
Figure
CE 2
327
86, PE 1 establishes two PWs