FCoE – Considerations for Deploying FCoE

Converged Enhanced Ethernet

  • Lossless Ethernet must be FoE aware
  • FIP snooping

Encapsulation

  • Maximum size frame is 2240 bytes
  • Mini-jumbo frame support is required
  • Not an issue for direct connect environments today
  • 802.1q tag carried CoS information

Data Center Bridging Capability eXchange Protocol (DCBX)

  • Extension of the link layer discovery protocol (LLDP)
  • Allows for exchange of priority map values for both FCoE and the FCoE initialization protocol (FIP)
  • Enables lossless behavior

FIP – FCoE Initialization Protocol

  • Bridges the gap between the expectations of FC and the reality of FCoE
  • Allows initiators and targets to know who to login with
  • One-to-many relationship is built in
  • LKA (link keep alive) and FIP CVL (clear virtual links) allows for logout from fabric should the logical link be lost
  • Implicit security (man-in-the-middle is difficult) provided that FIP snooping and dynamic ACLs are implemented
  • However, FCoE with FIP is more complex and more open for mis-configuration issues
  • Allows enode to:
    • Perform VLAN and FCF discovery
    • Ensure that the layer 2 network is capable of supporting mini-jumbo frames
    • Fabric login
    • LKA protocol
  • FIP VLAN request
    • Multi-cast
    • Allow the enode (CNA) to discover which VLANs FCoE services are being provided
    • All FIP requests and responses use a pre-defined set of TLV (type, length, value) data structures.
  • FIP VLAN notification
    • Unicast
    • Both FCFs response
  • FIP Solitication
    • Multicast
    • Allows the enode to discover which FCFs (fibre channel forwarders) are available for login
    • 802.1q tag and max FCoE size field tag
  • FIP Advertisement
    • Unicast
    • Note the priority, name id (fabric WWN), and max FCoE size
    • Max FCoE size is a field padded to the proper size (2158 bytes in length)
    • Dynamic ACL updated via FIP snooping
  • FIP FLOGI
    • Unicast
    • The FCF with the lower priority is sent the FLOGI

Priority Flow Control (PFC)

  • Necessary since FC requires lossless environment
  • Without PFC, normal periodic SAN congesntion will cause frames to drop
  • Uses 8 transmissions lines with independent transmit queues and receive buffers
  • Maximum distance is today is 50 meters. Not a hard limit. It’s a function of the high water mark of the buffer and ?? (missed that detail)

Use cases

  • Already have investment in FC or are building a new DC
  • Already have a LAN that supports 10 GE to core
  • FCFs today are anywhere between 2.5:1 – 5:1 oversubscribed (assumes FCoE switch is fully pop’ed with CNAs, will be solved when FCoE functionality is integrated into director class switches)

Physical Connectivity

  • Twinax (copper) and short range optical (fibre)
    • Twinax is much cheaper then fibre solutions (1/10 the cost)
    • Twinax uses less power

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