I'm currently using the HP Procurve 2824 24-port Gigabit Ethernet switch to for a backside network for synchronizing file systems between the nodes in the group. Each host has 4 Gigabit NIC's and the goal is to bond two of the Gigabit NIC's together to create a 2 Gbps link from any host to any other host but what I'm finding is that the bonded links are only capable of 1 Gbps from any host to any other host. Is it possible to
create a multi-Gigabit link between two hosts (without having to upgrade
to 10G) using a switch that "uses the
SA/DA (Source Address/Destination Address) method of distributing
traffic across the trunked links"?
The problem, at least as far as I can tell, comes down to the
limitation of ARP resolution (in the host) and mac-address tables (in
the switch):
When configured to use IEEE 802.3ad (LACP),
the kernel driver assigns the same MAC address to all of the hosts'
interfaces. In this scenario, when Host A sends traffic to Host B, the
kernel uses Host B's shared MAC address as the DA. When the packet
arrives at the switch, the switch creates a hash based on the SA/DA
pair, consults the mac-address table for the DA, and and assigns the
flow (i.e., traffic from Host A to Host B) to one of the interfaces
connected to Host B. Thus packets from Host A to Host B will only leave
the switch through one interface - the interface determined by the SA/DA hash.
This has the effect of limiting the throughput from Host A to Host B to
the speed of the one interface determined by the hashing method. However, if the flow (from Host A to Host B's shared MAC
address) were to be distributed across the different interfaces in a
round-robin
fashion (as the
packets were leaving the switch) the throughput between the hosts would
equal the aggregate of
the links (IIUC).
Is this a limitation of the the Procurve's implementation of LACP? Do other switches use different methods of distributing traffic across the trunked links? Is there another method of aggregating the links between the two hosts (e.g., multipathing)?
TIA,
Eric Pretorious
Truckee, CA
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