Users Guide

The logical FCF must be projected only if there is at least one operationally up FC uplink; this FC uplink must have successfully
completed the initial login with upstream switch at the time of timer expiry. This behavior achieves better load balancing during
boot-up and bulk configuration.
Even though all the uplinks are projected as one FCF, when a request for session establishment is received, the system finds
the optimally loaded FC uplink. The load balancing algorithm makes use of the link's session count and the link speed as factors
for session re-balancing. Session count of the uplink is the count of both Fabric login sessions (FLOGI) and Fabric discovery
sessions (FDISC) in that uplink. Link speed will be the speed of the FC uplinks. End devices do not have control over the link
chosen for session establishment. This behavior ensures better load balancing across the available uplinks. After the session is
established, the FCoE/FC data traffic is re-directed to the appropriate port to which the login request was associated.
Now the logical FCF takes care of the FIP functionality in the VLAN configured for the fabric. With this implementation, all
control frames originating from the logical FCF use a system generated MAC address instead of the port's MAC address. This
system generated MAC address of logical FCF is same for all the fabrics configured in the gateway switch; because, every FCF
is uniquely identified by the end device using VLAN-MAC address pair and the VLAN used is unique for every fabric. As a result,
the same MAC address is used for all the fabrics.
The control frames such as FCF Discovery Advertisement and Login Request or Response from logical FCF(s) in a gateway
switch have the gateway switch's world wide name(WWN) instead of upstream switch's WWN as Fabric name inside Fabric
descriptor. As a result, while forwarding the control traffic from upstream, it is the responsibility of the gateway switch to
modify the fabric descriptor in those frames with the logical FCF's fabric name.
When an uplink interface in the gateway switch becomes operationally down, all the sessions associated with that uplink are
terminated by sending a session termination request(CVL/FLOGO) to the corresponding end devices. When the end devices
requests for re-establishment of those sessions, those devices are allocated to the next optimal (least loaded) link available in
the fabric.
The manual load re-balance done using a management interface command has no impact and it continues to do load re-
balancing across the upstream ports(instead of FCFs) available in the gateway switch. You must mention the fabric id while
triggering and can monitor the load re-balancing in the gateway switch using the corresponding management interface display
commands such as show npg uplink-interface.
NOTE:
This feature is currently supported in S4148U and MX9116n platforms as NPG mode is supported only in platforms
where Fibre Channel ports are available.
Restrictions and Limitations
Connecting uplinks of the same fabric in a Gateway switch to two different SAN networks is an invalid configuration. If you
connect the same fabric in a gateway to two different SAN networks, the following scenarios may occur:
● There is no conflict in FC address assignment between the fabrics - This scenario leads to reduced visibility. End devices can
only talk to the other end devices connected to the same fabric.
● There is conflict in FC address assignment. The following scenarios may further occur:
○ If the conflict occurs for the FC uplink interface's initial login, the corresponding FC session is closed. Initial login is
retried till an unique address within NPG fabric context is assigned with a longer retry time out period(10 seconds). Untill
login succeeds, this interface will not be a part of the logical FCF.
○ If the conflict occurs for a forwarded login request (FLOGI/FDISC), the older session with the same FC-ID survives and
the newer session is teared down or rejected. This behavior is notified to the user through logs visible to the customer.
The reason for the error is set and the duplicate FC Id counter variable is incremented.
Usecase 1 - NPG fabric is connected to an FCF switch through
multiple links
Consider a topology where the gateway switch is connected to an upstream switch through multiple links.
The gateway switch is an OS10 switch operating in NPG mode and with two FC upstream interfaces (fc 1/1/1 and fc 1/1/2)
having a speed of 16G.
Two FCoE end points(CNAs) are attached to ports eth 1/1/54 and eth 1/1/55 and they carry FCoE traffic. FC end points
(HBAs) are attached to ports fc 1/1/9 and fc 1/1/10 and they carry pure FC traffic.
Both FCoE traffic and FC traffic is balanced across the FC upstream interfaces (fc 1/1/1 and fc 1/1/2) available in the NPG
switch.
Following configurations are to be done in the NPG switch:
NPG Device Configuration
Fibre Channel
485