HP 5920 Series Configuration Manual page 8

The outer Ethernet header enables traditional Ethernet switches to forward TRILL frames and
connect RBs.
Multidestination frame forwarding mechanism.
•
In a TRILL network, RBs perform the following tasks:
Compute a TRILL distribution tree for each VLAN based on the LSDB.
Guide the forwarding of multidestination frames in each VLAN by using its TRILL distribution
tree.
As shown in Figure
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
de-encapsulated 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 Layer 2 multicast frame forwarding flow
S1
VLAN 10
Inner D-MAC = Multi
Inner S-MAC = S1
Inner VLAN = 10
Payload
Ethernet frame
Multicast frame
TRILL selects distribution trees for forwarding multidestination frames based on the VLANs to which
the frames belong. Because the topologies of TRILL distribution trees are different, traffic can be
load shared. However, equal-cost links are not used for load sharing.
When N equal-cost links exist in the network, each TRILL distribution tree selects the link with the
largest pseudonode ID for forwarding packets. As shown in
between RB 1 and RB 3. Assume the link directly connecting RB 1 to RB 3 has the largest
pseudonode ID. Both the TRILL distribution tree rooted at RB 3 and the TRILL distribution tree rooted
3, when a multicast frame from VLAN 10 enters the TRILL network, RB 1, which
VLAN 200
TRILL network
RB 1
Outer D-MAC = All RBs
Outer S-MAC = RB 1
Outer VLAN = 200
Egress RB = RB 2
Ingress RB = RB 1
Inner D-MAC = Multi
Inner S-MAC = S1
Inner VLAN = 10
Payload
TRILL frame
Distribution tree
of VLAN 10
4
RB 4
RB 2
Outer D-MAC = All RBs
Outer S-MAC = RB 2
Outer VLAN = 200
Egress RB = RB 2
Ingress RB = RB 1
Inner D-MAC = Multi
Inner S-MAC = S1
Inner VLAN = 10
Payload
TRILL frame
Root bridge of
distribution tree
Figure
S2
RB 3
VLAN 10
Inner D-MAC = Multi
Inner S-MAC = S1
Inner VLAN = 10
Payload
Ethernet frame
Leaf of
distribution tree
4, two equal-cost links exist