312
To establish BGP PWs, BGP advertises label block information in an extended BGP update to
PEs in the same VPN. Each PE uses the received label block information to calculate outgoing
labels and uses its own label block to calculate incoming labels. After two PEs complete label
calculation, a BGP PW is established between them. BGP PWs have the following features:
Simplified configuration
—There is no need to manually specify peer PEs. A PE
automatically find peer PEs after receiving label block information from the peer PEs.
Reduced workload
—Label block advertisement enables assigning labels for multiple PWs
at one time.
To establish a CCC PW, manually specify the incoming and outgoing labels for the CCC PW on
the PEs, and create two static LSPs in opposite directions on P devices between PEs. CCC
employs only one level of label to transfer packets. The static LSPs on the P devices transfer
data only for the CCC PW. They cannot be used by other connections or MPLS L3VPN.
3.
Set up an AC between a PE and a CE:
Set up an AC by configuring a link layer connection between a PE and a CE.
An AC is an Ethernet service instance on a Layer 2 Ethernet interface or Layer 2 aggregate
interface. The interface forwards incoming packets that match the Ethernet service instance to
the bound PW.
4.
Bind the AC to the PW:
Bind the Ethernet service instance to the PW, so the PE forwards packets between the AC and
the PW.
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
, PE 1 establishes two PWs
(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 83 PW redundancy
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.
CE 1
PE 3
PE 1
PE 2
CE 2
MPLS or IP backbone
Primary
PW
Backup PW
