H3C Technologies H3C S6300 Series Switches - Manual (Page 12)

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Figure 4 Multicast ECMP
TRILL distribution trees support Equal Cost Multiple Path (ECMP), also known as multicast ECMP. When
multicast ECMP is enabled, TRILL assigns equal-cost links to different TRILL distributions trees. This
improves the load sharing performance.
When N equal-cost links exist in the network, each TRILL distribution tree selects an equal-cost link for
forwarding packets through J mod N in root bridge priority order. J is the priority sequence number of a
TRILL distribution tree and starts from 0.
As shown in
Figure 4 :
• The link directly connecting RB 1 to RB 3 is assigned to the TRILL distribution tree rooted at RB 3.
• The link RB 1-RB 2-RB 3 is assigned to the TRILL distribution tree rooted at RB 4.
TRILL distribution trees support fast root switching. When an RB detects that the root of a distribution tree
is unreachable, the RB deletes the LSP of the root from its LSDB. This triggers recalculation of all
distribution trees in the TRILL network. Multicast, broadcast, and unknown unicast traffic is switched to
new distribution trees.
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
• RFC 1195, Use of OSI IS-IS for Routing in TCP/IP and Dual Environments
Configuration restrictions and guidelines
When you configure TRILL, follow these restrictions and guidelines:
• Configuration in Layer 2 Ethernet interface view takes effect on only the current port. Configuration
in Layer 2 aggregate interface view takes effect on the current interface and its member ports.
Configuration on a member port of an aggregate interface takes effect after the member port
leaves the aggregation group.
• To connect a spanning tree network to a TRILL network, make sure the following requirements are
met:
{
The spanning tree protocol is disabled on the TRILL network.
{
An edge port connects the spanning tree network to the TRILL network, and BPDU guard is
enabled on the edge port. This allows the port to transit to the forwarding state before DRB
election is finished and prevents multiple DRBs from being elected.
RB 1 RB 2
RB 3
RB 4
Cos
t =
3
Cost = 1