H3C Technologies H3C S12500-X Series Switches - Manual (Page 10)

4
Multi-destination frame forwarding mechanism
In a TRILL network, RBs do the following:
• Compute a TRILL distribution tree for each VLAN according to the LSDB.
• Use the TRILL distribution tree to guide the forwarding of multi-destination frames, which include
multicast, broadcast, and unknown unicast frames in the VLAN.
As shown in Figure 3 , when a multicast frame from VLAN 10 enters the TRILL network, RB 1, which is an
ingress RB, encapsulates the multicast frame into a TRILL frame. In the frame, the egress RB is RB 2, the
root bridge of the TRILL distribution tree for VLAN 10. When the frame arrives at the root bridge, it is
distributed throughout the TRILL distribution tree. Then, the TRILL frame is decapsulated by RB 3 and sent
to the destination station S2. Because the network segment where RB 4 resides does not have a receiver
of this frame, RB 4 drops the frame.
Figure 3 Multicast frame forwarding flow
Protocols and standards
• RFC 6325: Routing Bridges (RBridges): Base Protocol Specification
• RFC 6326: Transparent Interconnection of Lots of Links (TRILL) Use of IS-IS
• RFC 6327: Routing Bridges (RBridges): Adjacency
VLAN 10 VLAN 10
S1 S2
VLAN 200
TRILL network
RB 1
Ethernet frame
Payload
Inner VLAN = 10
Inner S-MAC = S1
Inner D-MAC = Multi
TRILL frame
Ingress RB = RB 1
Outer VLAN = 200
Egress RB = RB 2
Outer S-MAC = RB 1
Outer D-MAC = All RBs
Payload
Inner VLAN = 10
Inner S-MAC = S1
Inner D-MAC = Multi
TRILL frame
Ingress RB = RB 1
Outer VLAN = 200
Egress RB = RB 2
Outer S-MAC = RB 2
Outer D-MAC = All RBs
Payload
Inner VLAN = 10
Inner S-MAC = S1
Inner D-MAC = Multi
RB 4
RB 3
Ethernet frame
Payload
Inner VLAN = 10
Inner S-MAC = S1
Inner D-MAC = Multi
RB 2
Multicast frame
Distribution tree
of VLAN 10 Root bridge of
distribution tree Leaf of
distribution tree