Dell Brocade G620 Brocade 8.0.1 Fabric OS Administratiors Guide - Page 109

Fibre Channel NAT, Inter-switch links

Page 109 highlights

Routing Traffic Destination ID (DID). When an ISL is attached or removed from a switch, FSPF updates the route tables to reflect the addition or deletion of the new routes. As each host transmits a frame to the switch, the switch reads the SID and DID in the frame header. If the domain ID of the destination address is the same as the switch (intra-switch communications), the frame buffer is copied to the destination port and a credit R_RDY message is sent to the host. The switch only needs to read word zero and word one of the Fibre Channel frame to perform what is known as cut-through routing. A frame may begin to emerge from the output port before it has been entirely received by the input port. The entire frame does not need to be buffered in the switch. If the destination domain ID is different from the source domain ID, then the switch consults the FSPF route table to identify which local E_Port provides Fabric Shortest Path First (FSPF) to the remote domain. Fibre Channel NAT Within an edge fabric or across a backbone fabric, the standard Fibre Channel FSPF protocol determines how frames are routed from the source Fibre Channel (FC) device to the destination FC device. The source or destination device can be a proxy device. Fibre Channel fabrics require that all ports be identified by a unique port identifier (PID). In a single fabric, FC protocol guarantees that domain IDs are unique, and so a PID formed by a domain ID and area ID is unique within a fabric. However, the domain IDs and PIDs in one fabric may be duplicated within another fabric, just as IP addresses that are unique to one private network are likely to be duplicated within another private network. In an IP network, a network router can maintain network address translation (NAT) tables to replace private network addresses with public addresses when a packet is routed out of the private network, and to replace public addresses with private addresses when a packet is routed from the public network to the private network. The Fibre Channel routing equivalent to this IP-NAT is Fibre Channel network address translation (FC-NAT). Using FC-NAT, the proxy devices in a fabric can have PIDs that are different from the real devices they represent, allowing the proxy devices to have appropriate PIDs for the address space of their corresponding fabric. Inter-switch links An inter-switch link (ISL) is a link between two switches, E_Port-to-E_Port. The ports of the two switches automatically come online as E_Ports once the login process finishes successfully. For more information on the login process, refer to Understanding Fibre Channel Services on page 25. You can expand your fabric by connecting new switches to existing switches. Figure 6 shows a new switch being added into an existing fabric. The thick red line is the newly formed ISL. Brocade Fabric OS Administration Guide, 8.0.1 53-1004111-02 109

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Destination ID (DID). When an ISL is attached or removed from a switch, FSPF updates the route tables to reflect the addition or deletion
of the new routes.
As each host transmits a frame to the switch, the switch reads the SID and DID in the frame header. If the domain ID of the destination
address is the same as the switch (intra-switch communications), the frame buffer is copied to the destination port and a credit R_RDY
message is sent to the host. The switch only needs to read word zero and word one of the Fibre Channel frame to perform what is
known as
cut-through routing
. A frame may begin to emerge from the output port before it has been entirely received by the input port.
The entire frame does not need to be buffered in the switch.
If the destination domain ID is different from the source domain ID, then the switch consults the FSPF route table to identify which local
E_Port provides Fabric Shortest Path First (FSPF) to the remote domain.
Fibre Channel NAT
Within an edge fabric or across a backbone fabric, the standard Fibre Channel FSPF protocol determines how frames are routed from
the source Fibre Channel (FC) device to the destination FC device. The source or destination device can be a proxy device.
Fibre Channel fabrics require that all ports be identified by a unique port identifier (PID). In a single fabric, FC protocol guarantees that
domain IDs are unique, and so a PID formed by a domain ID and area ID is unique within a fabric. However, the domain IDs and PIDs in
one fabric may be duplicated within another fabric, just as IP addresses that are unique to one private network are likely to be duplicated
within another private network.
In an IP network, a network router can maintain network address translation (NAT) tables to replace private network addresses with public
addresses when a packet is routed out of the private network, and to replace public addresses with private addresses when a packet is
routed from the public network to the private network. The Fibre Channel routing equivalent to this IP-NAT is Fibre Channel network
address translation (FC-NAT). Using FC-NAT, the proxy devices in a fabric can have PIDs that are different from the real devices they
represent, allowing the proxy devices to have appropriate PIDs for the address space of their corresponding fabric.
Inter-switch links
An inter-switch link (ISL) is a link between two switches, E_Port-to-E_Port. The ports of the two switches automatically come online as
E_Ports once the login process finishes successfully. For more information on the login process, refer to
Understanding Fibre Channel
Services
on page 25.
You can expand your fabric by connecting new switches to existing switches.
Figure 6
shows a new switch being added into an existing
fabric. The thick red line is the newly formed ISL.
Routing Traffic
Brocade Fabric OS Administration Guide, 8.0.1
53-1004111-02
109