McDATA StorageWorks 2/140 - Director Switch Planning Manual page 164

Implementing SAN Internetworking Solutions
4
iFCP Operation
McDATA Products in a SAN Environment - Planning Manual
4-22
There are three protocols competing to transmit storage-related I/O
traffic over long-distance transmission control protocol/Internet
protocol (TCP/IP) links:
• iSCSI is a TCP/IP-based protocol for establishing and managing
connections between IP-based storage devices, hosts, and clients.
iSCSI operates on top of TCP, moving block data (iSCSI packets)
over an IP Ethernet network. Refer to
information.
• iFCP is a gateway-to-gateway protocol that connects distributed
Fibre Channel SAN islands (or mSANs) through a TCP/IP
infrastructure. With iFCP, each connected fabric is maintained
separately from the others, while the IP network provides
connectivity, congestion control, error detection, and error
recovery.
• FCIP - Fibre Channel over IP (FCIP) is a TCP/IP-based protocol
for connecting geographically distributed Fibre Channel SANs.
FCIP requires installation of an edge device between a Fibre
Channel SAN and the IP network, and encapsulates Fibre
Channel frames into IP packets and fabric domains to IP
addresses. This process of encapsulating one information packet
inside another is called protocol tunneling. With FCIP, a single
SAN fabric is created by connecting multiple SAN islands
through IP network tunnels.
Typical SAN extension technologies build a single Fibre Channel
fabric between two remote locations. The resulting long-distance
(stretched E_Port) connection may be a direct, native Fibre Channel
link (through WDM equipment or dark fiber) or an FCIP link. Using
WDM equipment or repeaters, native Fibre Channel extension
supports metropolitan distances up to 75 miles (120 km). FCIP
supports greater distances by providing a tunneling protocol that
encapsulates Fibre Channel data and forwards it over a TCP/IP
network.
When two or more Fibre Channel fabrics are connected (through
direct connection, WDM, or FCIP), standard fabric building and
principal switch selection occurs. Whether two fabric switches are
separated by a few feet or by hundreds of miles, establishing
connectivity between E_Ports may trigger a disruptive or non-
disruptive build fabric event. In fact, a stretched E_Port is vulnerable
to disruptions caused by events at each site and to disruptions caused
by problems with the extended-distance TCP/IP link.
iSCSI Protocol for additional