FA leverages LLDP to discover directly connected FA peers and to exchange information associated with FA amongst those peers. FA information is transmitted using company-specific proprietary organizational Type, Length, Value (TLV) fields within LLDP Protocol Data Units (PDU). The following section describes the TLVs for FA.
FA uses two TLVs:
FA Element TLV
FA Assignment TLV
The FA Element TLV is used by FA elements to advertise Fabric Attach capabilities. This data forms the basis for FA element discovery and is used in the initial handshake between the FA Server and a client or proxy device.
Field |
Description |
---|---|
TLV Type |
Indicates whether the discovered element is a client or a proxy device. |
OUI and Subtype |
The information in these fields is used in LLDP packet handling. |
HMAC-SHA Digest |
Data integrity and source validation is supported through the use of the HMAC-SHA256 message authentication. This field supports a digest exchange between the source and destination devices. Symmetric private keys are used for digest generation. The HMAC-SHA256 generated digest size is 32 octets. The HMAC-SHA256 digest is computed starting with the Element Type data, that is, it starts at zero-based byte 38 of the TLV. The digest is then placed in the HMAC-SHA256 Digest field in the TLV prior to transmission. Upon receipt, the digest is again computed and the resulting digest is compared against the received digest. If the received digest is the same as the newly computed digest, the TLV is considered valid and processing commences. If the comparison fails, the TLV is discarded and processing is terminated. Caution:
If FA communication occurs between non-secure systems, the HMAC-SHA256 Digest data must always be zero. If one system operates in secure mode and the other operates in non-secure mode, the FA Element TLV is discarded before it is processed by the system operating in secure mode. |
Element Type |
Indicates the supported element type. The primary element types are the FA Server, FA Proxy, and FA Client. An FA Server is an SPB capable device that accepts externally generated I-SID-to-VLAN assignments. An FA Proxy is a non-SPBM device that supports I-SID-to-VLAN assignment definitions and advertises these assignments for possible use by an FA Server. An FA Client, also a non-SPBM device, advertises I-SID-to-VLAN assignments to a directly connected FA Proxy or an FA Server. Both tagged and untagged FA Client connections are supported. The list of supported element types and their values are:
|
State |
Indicates the link tagging requirements in FA Client-sourced frames. This field also indicates the current provisioning mode. The Link VLAN Tagging bit (bit 1) has one of the following values:
The automatic provisioning mode bits (bits 2 and 3) always have the value 1 for SPB provisioning. The switch only supports the SPB provisioning mode. |
Mgmt VLAN |
When you configure a management VLAN on the FA Server, it is included in this field in FA Server or FA Proxy sourced frames, and is used to support management VLAN auto-configuration on the downstream proxy and client devices. |
System ID |
This field contains connection information that a TLV recipient can use to enforce connectivity restrictions. It contains the system MAC address (6 octets) for MLT configurations and the virtual BMAC address for vIST and SMLT configurations. It also contains information on the connection type such as MLT or SMLT. |
The FA Element TLV exists only once in an LLDP PDU and is included in all PDUs when the FA service is enabled.
The maximum length of the FA Element TLV is 56 bytes.
The FA I-SID-to-VLAN Assignment TLV is used by FA Clients to distribute I-SID-to-VLAN assignments that need to be supported by an FA Proxy or an FA Server.
Some fields are common to both the FA Element and FA Assignment TLVs. The following fields are specific only to the FA Assignment TLV.
TLV Field |
Description |
---|---|
HMAC-SHA Digest |
The HMAC-SHA256 digest is computed for the series 1 to 94 of I-SID-to-VLAN assignments, that is, the data for the digest computation starts at zero-based byte 38 of the TLV. The digest is then placed in the HMAC-SHA256 Digest field in the TLV prior to transmission. Upon receipt, the digest is again computed for the series 1 to 94 of I-SID-to-VLAN assignments in the received TLV and the resulting digest is compared against the received digest. If the received digest is the same as the newly computed digest, the TLV is considered valid and processing can commence. If the comparison fails, the TLV is discarded and processing is terminated. Caution:
If FA communication occurs between non-secure systems, the HMAC-SHA256 Digest data must always be zero. If one system operates in secure mode and the other operates in non-secure mode, the FA I-SID-toVLAN Assignment TLV is discarded before it is processed by the system operating in secure mode. |
Assignment status |
Indicates whether the FA Server accepted or rejected the I-SID-to-VLAN mapping request from a client or proxy device. |
VLAN |
Indicates the C-VID value advertised by the client or proxy device in the FA I-SID-to-VLAN mapping request. |
I-SID |
Indicates the I-SID that is advertised by a client or proxy device in the FA I-SID-to-VLAN mapping request. This I-SID is used to create a Switched UNI (ELAN) I-SID. Note:
This I-SID cannot be used by IPVPN, MVPN, SPBM dynamic multicast range, or Transparent Port UNI. |
The FA I-SID-to-VLAN Assignment TLV is included in an LLDP PDU only if the FA Server and proxy or client devices are directly connected to each other.
This TLV can exist only once in an LLDP PDU.
The size limit of this TLV is 511 bytes. This limits the maximum number of I-SID-to-VLAN assignments supported in an LLDP PDU to 94.
For an FA I-SID-to-VLAN Assignment TLV to be processed, the FA Element TLV must also be present in the LLDP PDU.