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LAG to combine multiple "slow" links
Please excuse my n00b question but would a LAG between a pair of PowerConnect 5424s be a suitable way to combine the bandwith from 3-4 comparatively slow links in order to allow a single machine/TCP connection to exceed the amount of bandwidth offered by one of these slow links on their own?
I've used LAGs in iSCSI SAN switches with success in the past and initially thought it would work for this application. I haven't found it explicitly mentioned, in terms dumb enough for me to understand, but from what I've read it seems to indicate that no individual device/TCP connection can exceed the amount of bandwidth offered by one of the LAG member ports. In other words, a group of devices can collectively take advantage of all of the LAG's available bandwidth but not a single device on switch A, connecting to a single device on switch B. Is this the case? Or is this just the way it typically plays out when all connections involved are 1 gigabit, full duplex?
Let's say you have a 4 port LAG group at 100 mbps, full duplex, could a single 1 gig device on switch A connect to a single 1 gig device on switch B at 400 mbps? Or would it be limited to 100 mbps?
If a LAG isn't the way to go about this what would be more appropriate? I don't really have the option of physical NIC teaming on the client devices. I can give more specific details about the scenario if anyone would like to hear that.
Thanks,
Jeff
DELL-Willy M
802 Posts
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November 26th, 2012 16:00
If I understand what you are stating correctly I do not think that is possible. You will need a team or a device that is lag compatible on the other end to take advantage of the LAG features. If you are setting a LAG up with 2 ports. You will have to connect 2 physical cables to the designated ports and then mirror the set up on the other end of the LAG.
Here is some information on Link Aggregation:
Up to eight Aggregated Links may be defined, each with up to eight member ports, to form a single Link
Aggregated Group (LAG). This enables:
• Fault tolerance protection from physical link disruption
• Higher bandwidth connections
• Improved bandwidth granularity
• High bandwidth server connectivity
LAG is composed of ports with the same speed, set to full-duplex operation..
Port Channel Mode
The Port Channel mode contains commands for configuring Link Aggregation Groups (LAG).
The following is an example of the Port Channel mode prompt:
Console (config)# interface port-channel 1
Console (config-if)#
Aggregating Ports
Port Aggregation optimizes port usage by linking a group of ports together to form a single Link
Aggregated Group (LAG). Port Aggregation multiplies the bandwidth between the devices, increases
port flexibility, and provides link redundancy. The device supports up to eight LAGs per system, and
eight ports per LAG per device.
Each LAG is composed of ports of the same speed, set to full-duplex operations. Ports in a LAG, can be of different media types (UTP/Fiber, or different fiber types), provided they operate at the same speed.
Aggregated Links can be assigned manually or automatically by enabling Link Aggregation Control
Protocol (LACP) on the relevant links. The device provides LAG Load Balancing based on both source
MAC addresses and destination MAC addresses.
Aggregated Links are treated by the system as a single logical port. Specifically, the Aggregated Link has similar port attributes to a non-aggregated port, including auto-negotiation, speed, Duplex setting, etc.
The device supports both static LAGs and Link Aggregation Control Protocol (LACP) LAGs. LACP
LAG negotiate Aggregated Port links with other LACP ports located on a different device. If the other
device ports are also LACP ports, the devices establish a LAG between them.
The following guidelines should be followed when adding ports to a LAG:
• There is no Layer 3 interface defined on the port.
• The port does not belong to any VLAN.
• The port does not belong to any other LAG.
• The port is not a mirrored port.
• The port's 802.1p priority is equal to LAGs 802.1p priority.
• QoS Trust is not disabled on the port.
• GVRP is not enabled.
Ports can be configured as LACP ports only if the ports are not part of a previously configured LAG.
The device uses a hash function to determine which frames are carried on which aggregated-link
member. The hash function statistically load-balances the aggregated link members. The device
considers an Aggregated Link as a single logical port.
Each Aggregated Link has an Aggregated Link Port Type, including Gigabit Ethernet ports. Ports can be added to an Aggregated Link only if they are the same port type. When ports are removed from an Aggregated Links, the ports revert to the original port settings. To open the Link Aggregation page,
click Switch→Link Aggregation in the tree view.
Hope this helps,