Bpdu Tunneling Implementation - H3C SR8800 Configuration Manual

BPDU Tunneling implementation

NOTE:
The term
•
STP calculates the topology of a network by transmitting BPDUs among bridges in the network. For
•
details, see the chapter "Configuring the spanning tree."
To avoid loops in your network, you can enable STP on your routers. When the topology changes at one
side of the customer network, the routers at this side of the customer network send BPDUs to routers on the
other side of the customer network, thus ensuring consistent spanning tree calculation in the entire
customer network. However, because BPDUs are Layer 2 multicast frames, all STP-enabled routers, both
in the customer network and in the service provider network, can receive and process these BPDUs. In this
case, neither the service provider network nor the customer network can correctly calculate its
independent spanning tree.
To allow each network to calculate an independent spanning tree with STP, BPDU tunneling was
introduced.
BPDU tunneling delivers the following benefits:
BPDUs can be transparently transmitted. BPDUs of the same customer network can be broadcast in
•
a specific VLAN across the service provider network, so that the geographically dispersed networks
of the same customer can implement consistent spanning tree calculation across the service
provider network.
BPDUs of different customer networks can be confined within different VLANs for transmission on
•
the service provider network. Thus, each customer network can perform independent spanning tree
calculation.
Figure 37 BPDU tunneling implementation
As shown in
represents two different parts of a customer network: User A network 1 and User A network 2. Enabling
the BPDU tunneling function on the edge routers (PE 1 and PE 2) in the service provider network allows
BPDUs of the customer network to be transparently transmitted in the service provider network, thus
ensuring consistent spanning tree calculation of User A network, without affecting the spanning tree
calculation of the service provider network.
Assume a BPDU is sent from User A network 1 to User A network 2:
At the ingress of the service provider network, PE 1 changes the destination MAC address of the
1.
BPDU from 0x0180-C200-0000 to a special multicast MAC address, 0x010F-E200-0003 (the
STP
in this document is in a broad sense. It includes STP, RSTP, and MSTP.
Figure 37, the upper part is the service provider network (ISP network), and the lower part
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