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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 Packet Formats

TRILL Packet Formats

TRILL packets include TRILL control packets and TRILL data packets.

TRILL Control Packets

TRILL switches exchange control packets to communicate with each other. This section describes major TRILL control packets used on a TRILL network. TRILL uses IS-IS as the control plane protocol, uses PDUs to process control information, extends IS-IS PDUs.

TRILL PDUs use the same format as IS-IS PDUs, except that TRILL PDUs use extended IS-IS TLVs. For details on fields in a TRILL PDU, see "IS-IS Configuration" in the CloudEngine 8800, 7800, 6800, and 5800 Series switch Configuration Guide - IP Routing.

All PDUs used by TRILL can be classified into three types: Hello, LSP, and SNP. The first eight bytes are fixed in all TRILL PDUs, as shown in Figure 1-2.
Figure 1-2 TRILL PDU structure
The PDU fields are described as follows:
  • Intradomain Routing Protocol Discriminator: identifies a network-layer PDU.
  • Length Indicator: indicates the length of the fixed header.
  • ID Length: indicates the length of the intra-domain system ID.
  • PDU Type: indicates the PDU type.
  • Maximum Area Address: indicates the maximum number of area addresses allowed by TRILL. Currently, the TRILL area address can only be 00.
  • PDU Exclusive: varies depending on the PDU type and is described in the following PDU formats.
  • TLV: indicates the type/length/value, which varies depending on the PDU type.
TRILL Hello PDU Format

Hello PDUs are used to establish and maintain neighbor relationships. LAN Hello PDUs are used on broadcast networks and P2P Hello PDUs are used on non-broadcast networks. LAN Hello PDUs and P2P Hello PDU have different formats.

Figure 1-3 shows the LAN Hello PDU format.

Figure 1-3 LAN Hello PDU format

Figure 1-4 shows the P2P Hello PDU format.

Figure 1-4 P2P Hello PDU format

As shown in Figure 1-4, most fields in a P2P Hello PDU are the same as those in a LAN Hello PDU. The P2P Hello PDU does not have the priority and LAN ID fields, but has a local circuit ID field indicating the local link ID.


Link state PDUs (LSPs) are used to exchange link-state information. Figure 1-5 shows the LSP PDU format.

Figure 1-5 TRILL LSP PDU format

Sequence number PDUs (SNPs) describe the all or some of LSPs to synchronize and maintain all LSDBs. SNPs are classified into the following types:
  • Complete SNP (CSNP): carries summary of all LSPs in an LSDB, ensuring LSDB synchronization between neighboring switches. On a broadcast network, the DRB periodically sends CSNPs. The default interval for sending CSNPs is 10 seconds. On a point-to-point link, CSNPs are sent only when the neighbor relationship is established for the first time.

    Figure 1-6 shows the CSNP format.
    Figure 1-6 TRILL CSNP format

  • Partial SNP (PSNP): lists only the sequence numbers of recently received LSPs. A PSNP can acknowledge multiple LSPs at a time. If a device finds that its LSDB is not updated, it sends a PSNP to request a neighbor to send a new LSP.

    Figure 1-7 shows the PSNP format.
    Figure 1-7 TRILL PSNP format

TRILL Data Packets

Figure 1-8 shows the TRILL data packet format.
Figure 1-8 TRILL data packet format
A TRILL data packet is generated by adding a TRILL header and an outer Ethernet header to the original Ethernet packet. The fields in a TRILL header are described as follows:
  • Ethertype: fixed as TRILL.
  • V: version number, which is 0 currently. Each RB must check the version number when receiving a TRILL packet. If the version is incorrect, the RB discards the packet.
  • R: reserved for extension. This field is set to 0 on an ingress RB and ignored on transit and egress RBs.
  • M: multi-destination attribute. The value 0 indicates known unicast packets and the value 1 indicates multicast, broadcast, and unknown unicast packets.
  • Op-Length: length of the Options field. The value 0 indicates that the Options field is unavailable.
  • Hop-Count: used to prevent loops. When the Hop-Count field of a TRILL packet is set to 0, the RB discards the packet.
  • Egress RB Nickname: In a unicast packet, the field indicates the nickname of the egress RB. In a multicast packet, the field indicates the nickname of the multicast tree root used for forwarding.
  • Ingress RB Nickname: nickname of the ingress RB.
  • Options: This field is available only when the value of Op-Length is not 0.

For details on how TRILL data packets are forwarded on a TRILL network, see TRILL Forwarding Process.

Updated: 2019-05-08

Document ID: EDOC1100004349

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