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Configuration Guide - DCN and Server Management

CloudEngine 8800, 7800, 6800, and 5800 V200R003C00

This document describes the configurations of Trill, FCoE, DCB, and NLB Server Cluster Association.
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TRILL Forwarding Process

TRILL Forwarding Process

On a TRILL network, RBs send Hello packets to each other to establish neighbor relationships and send LSPs to synchronize LSDBs. After that, all RBs on a network have the same LSDB. Based on LSDB information, each RB then uses the SPF algorithm to calculate the shortest paths, outbound interfaces, and next hops to other RBs on the entire network. The RB uses the advised nickname information in the LSDB to generate a nickname forwarding table.

When user packets reach a TRILL network, they are forwarded in different processes based on the destination MAC addresses:

Process of Forwarding Known Unicast Traffic

Figure 1-13 illustrates how the known unicast traffic sent from server A to server C is forwarded.
Figure 1-13 Process of forwarding known unicast traffic
  1. The ingress RB (RB1) receives a Layer 2 packet from server A, and searches the Layer 2 forwarding table for the egress RB nickname matching the destination MAC address of the packet. After finding the egress RB nickname, RB1 looks up the unicast forwarding table to find the outbound interface L5 and next hop RB5 to the destination RB. RB1 then encapsulates the Layer 2 packet into a TRILL data packet and forwards the packet to the next hop through the outbound interface.
  2. When transit RB (RB5) receives the TRILL data packet, it obtains the egress RB nickname from the TRILL header and searches the unicast forwarding table for the egress RB nickname. Finding that the destination RB is RB6, RB5 forwards the TRILL data packet to RB6 through outbound interface L6.
  3. The egress RB (RB6) receives the TRILL data packet, and finds that the egress RB nickname in the TRILL header is its own nickname. Then RB6 decapsulates the TRILL packet to obtain the original Layer 2 data packet, and forwards the Layer 2 data packet through the matching outbound interface according to the destination MAC address of the packet.

Process of Forwarding Multicast, Broadcast, and Unknown Unicast Traffic

On a TRILL network, an RB calculates a distribution tree for each VLAN based on the LSDB to guide the forwarding of multicast, broadcast, and unknown unicast packets. Multicast packets are used as an example to describe the forwarding process, as shown in Figure 1-14.
Figure 1-14 Process of forwarding multicast traffic
  1. The ingress RB (RB1) receives a Layer 2 packet from server A, and finds that the destination MAC address is a multicast MAC address. RB1 selects the multicast distribution tree for the VLAN to which the packet belongs and encapsulates the Layer 2 packet in to a TRILL data packet. In the TRILL header, the M bit is set to 1, identifying a multicast packet. RB1 then looks up the multicast forwarding table according to the root RB nickname to find the outbound interface list, and forwards the TRILL packet to the outbound interface.
  2. The transit RB (RB4) receives the TRILL data packet, and checks the TRILL header. As the M bit in the TRILL header is 1, RB4 looks up the multicast forwarding table according to the egress RB nickname in the TRILL header, and forwards the multicast packet to the outbound interfaces in the matching forwarding entry.
  3. The root RB (RB3) receives the TRILL data packet, and distributes the packet to all the outbound interfaces.
  4. The egress RB (RB6) decapsulates the TRILL data packet to obtain the original Layer 2 data packet and forwards the packet through the matching outbound interface.
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Updated: 2019-05-08

Document ID: EDOC1100004349

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