3com S7906E 설치 설명서

1-4

Figure 1-2 MAC learning and flooding on PEs

MAC A IP 1.1.1.2

PW 3

PW 1

PW 2

MAC B IP 1.1.1.3

PE 1

PE 2

PE 3

ARP broadcast

ARP response

VPN 1

Vlan 10, port 1

VPN 1

PW 1

VSI

MAC

Port

PE 1

VPN 1

PW 3

VSI

MAC

Port

PE 3

VPN 1

VSI

MAC

Vlan 10, port 1

PW 1

Port

PE 2

2) MAC address reclaim

Dynamic address learning must support refreshing and relearning. The VPLS draft defines a dynamic

address learning method that uses the address reclaim message, which carries MAC TLV. Upon

receiving such a message, a device removes MAC addresses or relearns them according to the

specified parameters in the TLV. If NULL is specified, the device removes all MAC addresses of the VSI

except for those learned from the PW that received the address reclaim message.

The address reclaim message is very useful when the network topology changes and it is required to

remove the learned MAC addresses quickly. There are two types of address reclaim messages: those

with MAC address lists and those without MAC address lists.

After a backup link becomes active and a message with the instruction of relearning MAC entries

arrives, a PE updates the corresponding MAC entries in the FIB table of the VPLS instance and sends

the message to other PEs that are directly connected through LDP sessions. If the message contains a

null MAC address TLV list, these PEs remove all MAC addresses from the specified VSI, except for

those learned from the PW that sent the message.

3) MAC address aging

Remote MAC addresses learned by a PE that are related to VC labels but no more in use need to be

aged out by an aging mechanism. The aging mechanism used here is the aging timer corresponding to

the MAC address. When receiving a packet whose source MAC address has an aging timer started, the

PE resets the aging timer.

VPLS loop avoidance

In general, Layer 2 networks use the Spanning Tree Protocol (STP) to avoid loops. This is not

applicable for VPLS networks because the users cannot sense the service provider network. Therefore,

enabling STP in the private networks means nothing to the service provider network. In VPLS, full mesh

and split horizon forwarding are used to avoid use of STP at the private network side.

Two methods for VPLS loop avoidance are supported: