Brocade Fabric OS FCIP Administrator's Guide v7.1.0 (53-1002748-01, March 2013)

Fabric OS FCIP Administrator’s Guide 35

53-1002748-01

Memory use limitations for large-device tunnel configurations

• The Neighbor Discovery ICMPv6 Solicitations and Advertisements are transmitted to the Layer

2 Ethernet multicast MAC address derived from the IPv6 source address (RFC 2464).

• ICMPv6 message types in RFC 4443 and ICMPv6 message types used for Neighbor Discovery

are supported.

• Path MTU Discovery (RFC 1981) is not supported on this implementation, requiring static

configuration of MTU size. The maximum MTU supported is 1500 bytes (including the 40-byte

fixed IPv6 header), the same as for IPv4. The minimum MTU allowed is 1280 bytes (including

the 40-byte fixed IPv6 header). Any network used for IPv6 FCIP circuits must support an MTU of

1280 bytes or larger. IPv6 fragmentation is not supported. The Layer 4 protocol ensures that

the PDU is less than the MTU (including headers).

• The IPv6 addressing currently cannot be used when implementing IPsec.

IPv6 with embedded IPv4 addresses

Only IPv4-compatible IPv6 addresses are supported. Only the low-order 32 bits of the address can

be used as an IPv4 address (high-order 96 bits must be all zeros). This allows IPv6 addresses to be

used on an IPv4 routing infrastructure that supports IPv6 tunneling over the network. Both

endpoints of the circuit must be configured with IPv4-compatible IPv6 addresses. IPv4-to-IPv6

connections are not supported. IPv4-mapped IPv6 addresses are not supported, because they are

intended for nodes that support IPv4 only when mapped to an IPv6 node.

Memory use limitations for large-device tunnel configurations

The FCIP data processing layer on the Brocade 7800 switch and each FX8-24 blade data processor

(DP) has access to reserved memory used for control block structure allocations. The FX8-24 blade

contains two DPs. One DP handles VE_Ports 22-31, while the other DP handles VE_Ports 12-31.

Each DP on the FX8-24 blade has a DRAM pool size of approximately 268 Megabytes, whereas the

7800 has a single DRAM pool of approximately 200 Megabytes. Use the following command to

display current consumption of the FCIP tunnel DP complex control block memory pool.

portshow xtun <slot/>vePort -dram2

FCIP tunnel processing will create more control blocks when any type of emulation feature is

enabled, such as FCP or FICON. In those cases, be sure to not include too many “devices’ in the

FCIP tunnel configuration. If too many devices are present or activated at one time, emulation

operations can be negatively impacted. Note that a configuration that works without emulation,

such as Fastwrite, Open Systems Tape Pipelining (OSTP), or FICON emulation, may not work when

emulation features are enabled.

Control blocks created during FCP traffic flow

For FCP traffic flows, FCIP tunnel processing creates control block structures based upon the

SID/DID pairs used between initiators and devices. If either Fastwrite or OSTP (read or write) is

enabled, additional structures and control blocks are created for each LUN on a SID/DID pair basis.

FCP protocol processing in an emulated tunnel configuration will create multiple control blocks for

each LUN if there are multiple SID/DID pairs that can be used to access those LUNs. Each FCP

identified SID/DID flow will be recorded in a structure called an ITN (initiator, target, nexus). Each

specific LUN on a SID/DID flow will have an ITL (initiator, target, LUN) control block created for the

flow. FCIP FCP emulation processing also creates a structure for each outstanding FC exchange

called a turbo write block (TWB).