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Brocade ISL with / without trunking

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Brocade ISL with / without trunking

If you have 2 fabrics (alle 4Gb/s Brocade Switchws with latest code), each with 2 Brocade san switches together with 2 isl links in eeach fabric, and servers with 2 hba's doing disk activity to an EVA4400 on all 4 paths in a Windows 2003 environment + some ESX 3.5 servers. There are no trunking licenses installed. All servers need to go through both switches on both fabrics to reach the EVA. Will the traffic only go through one isl pr. fabric, or is there any kind of load balancing between the isl's in the same fabric?
What would trunking give me?


Ivan Ferreira
Honored Contributor

Re: Brocade ISL with / without trunking

Please check this document, it has answers to your questions:

Por que hacerlo dificil si es posible hacerlo facil? - Why do it the hard way, when you can do it the easy way?

Re: Brocade ISL with / without trunking

HI Inex,

Without trunking Brocade doesnt have load balancing however it does support "load sharing" of equal cost ISL's.

You can run DLSSHOW to see if Dynamic Load Sharing is enabled.

And you can set this via the DLSSET.

To see routes of ISL's you can run the command urouteshow and ISLshow.

If both links are up at the same time you will see a load share and with DLS enabled you will see that while FSPF rules apply both ISL will share the links between Initiators and targets.
Sivakumar MJ._1
Respected Contributor

Re: Brocade ISL with / without trunking

Inter Switch Link (ISL) Trunking can dramatically improve the performance, manageability, and reliability. By aggregating up to four ISLs into a single logical 8 Gb/s trunk group, this feature supports efficient
high-speed communications throughout Storage Area Networks (SANs).

By optimizing available switch resources, ISL
Trunking decreases congestion. In addition, ISL Trunking reduces administrative workload since ISLs can be managed as a
single entity rather than individually. Moreover, ISL Trunking can significantly increase data availability: even if an individual
ISL failure occurs, I/O can continue at a reduced bandwidth as long as at least one ISL in the trunk group remains available.
Together, these capabilities give organizations a powerful and flexible tool to extract the greatest performance and value from
their SAN investments.

The ISL Trunking feature allows up to four Interswitch Links (ISLs) to merge logically into a single link. An ISL is a
connection between two switches through an Expansion Port (E_Port). When using ISL Trunking to aggregate bandwidth
of up to four ports, the speed of the ISLs between switches in a fabric is quadrupled.

For example, at 2 Gb/s speeds,
trunking delivers ISL throughput of up to 8 Gb per second. ISL Trunking supports high-bandwidth, large-scale SANs which
include core switches. The primary task of ISL Trunking is to route data and edge switches that aggregate connections to
servers and storage. ISL Trunking simplifies network design and reduces the cost of storage management by optimizing
bandwidth utilization and enabling load balancing of traffic at the frame-level.

The advantages of ISL Trunking is for example, it ensures optimal ISL bandwidth use across trunked links, while preserving in-order delivery.
ISL Trunking uses frame-level load balancing, as opposed to Fibre Channel Shortest Path First (FSPF), to achieve faster
fabric convergence, as well as higher availability in the fabric.
Routing without the ISL Trunking feature
Prior to the implementation of the ISL Trunking feature, device-level load sharing was done through Fibre Channel
networks that created ISLs and operated using the FSPF routing protocol. The FSPF routing protocol established and
communicated the shortest paths for data to be carried from source to destination. Although FSPF compliant switches
ensure fixed routing paths, and guarantee that all frames are delivered in order, congestion occurs if the aggregation of
the stream exceeds the capacity of one of the ISLs in the path. For example, four untrunked ISLs have a maximum
capacity of 2 Gb/s which provides for a maximum throughput of 8 Gb per second. Due to traffic that is not trunked, the
throughput of the four ISLs is:
2 Gb/s + 1.5 Gb/s +.5 Gb/s + 1 Gb/s, which gives a 5 Gb/s total.
This is because two 2 Gb/s data streams are competing for the same path.
Routing with the ISL Trunking feature
With ISL Trunking, four ISLs provide 8 Gb/s of total throughput. With the implementation of ISL Trunking, bandwidth is
shared across the trunked ISLs, permitting a total throughput of:
2 Gb/s + 1.5 Gb/s + 0.5 Gb/s + 1 Gb/s + 2 Gb/s, for a total 7 Gb/s in this case.
Because the trunk aggregates the four individual paths into one and preserves in-order deliver of frames, the total
throughput is increased compared to a non-trunked group of ISLs. ISL Trunking dynamically performs load balancing, at
the frame level, across a set of available links between two adjacent switches to establish a trunking group. Ports that
belong to a trunking group are called trunking ports. One port is used to assign traffic for the group, and is referred to as
the trunking master.
New Member

Re: Brocade ISL with / without trunking

Hi i've something similar, our customer have two sites connected by dwdm link based on nortel optera motr 10g cards with two DCx4 on each. Sites.
During this WE they added two new isl Links to the existent one, so now we have three isl link two E port on the same blade and one in other blade, but in one site the two switches did not create the trunking, if check in the routing tab under switch administrations i see two Lines for port 14 and one for port 15 but the 14 seems not be used.
Instead of on the other couple that on the routing tab i see the trunking and if i whant to check the performance if i choose the port 14 is not possibile i've to use the port 15 to monitor the trunking
And ideas? How to enable the trunking .