SAN Switching Overview
This chapter provides an overview of SAN switching for Cisco NX-OS devices. This chapter includes the following sections:
The Fibre Channel domain (fcdomain) feature performs principal switch selection, domain ID distribution, FC ID allocation, and fabric reconfiguration functions as described in the FC-SW-2 standards. The domains are configured per VSAN . If you do not configure a domain ID, the local switch uses a random ID.
Trunking, also known as VSAN trunking, enables interconnect ports to transmit and receive frames in more than one VSAN over the same physical link. Trunking is supported on E ports and F ports.
Virtual SANs (VSANs) partition a single physical SAN into multiple VSANs. VSANs allow the Cisco NX-OS software to logically divide a large physical fabric into separate, isolated environments to improve Fibre Channel SAN scalability, availability, manageability, and network security.
Each VSAN is a logically and functionally separate SAN with its own set of Fibre Channel fabric services. This partitioning of fabric services greatly reduces network instability by containing fabric reconfiguration and error conditions within an individual VSAN. The strict traffic segregation provided by VSANs can ensure that the control and data traffic of a specified VSAN are confined within the VSAN's own domain, which increases SAN security. VSANs can reduce costs by facilitating consolidation of isolated SAN islands into a common infrastructure without compromising availability.
You can create administrator roles that are limited in scope to certain VSANs. For example, you can set up a network administrator role to allow configuration of all platform-specific capabilities and other roles to allow configuration and management only within specific VSANs. This approach improves the manageability of large SANs and reduces disruptions due to human error by isolating the effect of a user action to a specific VSAN whose membership can be assigned based on switch ports or the worldwide name (WWN) of attached devices.
The Cisco SAN switches also implement trunking for VSANs. Trunking allows Inter-Switch Links (ISLs) to carry traffic for multiple VSANs on the same physical link.
Zoning provides access control for devices within a SAN. The Cisco NX-OS software supports the following types of zoning:
N port zoning-Defines zone members based on the end-device (host and storage) port.
Fibre Channel identifier (FC-ID)
Fx port zoning-Defines zone members based on the switch port.
WWN plus the interface index, or domain ID plus the interface index
Domain ID and port number (for Brocade interoperability)
iSCSI zoning-Defines zone members based on the host zone.
LUN zoning-When combined with N port zoning, logical unit number (LUN) zoning helps ensure that LUNs are accessible only by specific hosts, providing a single point of control for managing heterogeneous storage-subsystem access.
Read-only zones-An attribute can be set to restrict I/O operations in any zone type to SCSI read-only commands. This feature is useful for sharing volumes across servers for backup, data warehousing, and so on.
Broadcast zones-An attribute can be set for any zone type to restrict broadcast frames to members of the specific zone.
To provide strict network security, zoning is always enforced per frame using access control lists (ACLs) that are applied at the ingress switch. All zoning polices are enforced in the hardware, and none of them cause performance degradation. Enhanced zoning session-management capabilities further enhance security by allowing only one user at a time to modify zones.
Device Alias Services
The software supports Device Alias Services (device alias) on per VSAN and fabric wide. Device alias distribution allows you to move host bus adapters (HBAs) between VSANs without manually reentering alias names.
Fibre Channel Routing
Fabric Shortest Path First (FSPF) is the protocol used by Fibre Channel fabrics. FSPF is enabled by default on all Fibre Channel switches. You do not need to configure any FSPF services except in configurations that require special consideration. FSPF automatically calculates the best path between any two switches in a fabric. Specifically, FSPF is used to perform these functions:
Dynamically compute routes throughout a fabric by establishing the shortest and quickest path between any two switches.
Select an alternative path if a failure occurs on a given path. FSPF supports multiple paths and automatically computes an alternative path around a failed link. FSPF provides a preferred route when two equal paths are available.
Advanced Fibre Channel Features
You can configure Fibre Channel protocol-related timer values for distributed services, error detection, and resource allocation.
You must uniquely associate the WWN to a single switch. The principal switch selection and the allocation of domain IDs rely on the WWN. .
Fibre Channel standards require that you allocate a unique FC ID to an N port that is attached to an F port in any switch.
FC-SP and DHCHAP
The Fibre Channel Security Protocol (FC-SP) provides switch-to-switch and hosts-to-switch authentication to overcome security challenges for enterprise-wide fabrics. The Diffie-Hellman Challenge Handshake Authentication Protocol (DHCHAP) is an FC-SP protocol that provides authentication between Cisco SAN switches and other devices. DHCHAP consists of the CHAP protocol combined with the Diffie-Hellman exchange.
With FC-SP, switches, storage devices, and hosts can prove their identity through a reliable and manageable authentication mechanism. With FC-SP, Fibre Channel traffic can be secured per frame to prevent snooping and hijacking even over untrusted links. A consistent set of policies and management actions are propagated through the fabric to provide a uniform level of security across the entire fabric.
Fabric binding ensures Inter-Switch Links (ISLs) are enabled only between specified switches in the fabric binding configuration, which prevents unauthorized switches from joining the fabric or disrupting the current fabric operations. This feature uses the Exchange Fabric Membership Data (EEMD) protocol to ensure that the list of authorized switches is identical in all of the switches in a fabric.
Fabric Configuration Servers
The Fabric Configuration Server (FCS) provides discovery of topology attributes and maintains a repository of configuration information of fabric elements. A management application is usually connected to the FCS on the switch through an N port. Multiple VSANs constitute a fabric, where one instance of the FCS is present per VSAN.