Badkey Corner | Port Trunking. QNAP

Saturday 27th, February 2010

Port Trunking. QNAP02/27/2010 08:31 PM

A number of NAS models come with Dual-LAN ports which allow "Port Trunking" options whereby two network interfaces function as one to increase bandwidth beyond the limits of any single interface, while at the same time offering redundancy and load balancing for higher availability. Below is a list of supported port trunking modes. Note that some trunking and redundancy options require a switch that also supports these features. Please note that incompatible mode settings may cause the network interface to hang or affect overall network performance.

Field Description
Balance-rr (Round-Robin) Round-Robin mode is good for general purpose load balancing between the adapters. This mode transmits packets in sequential order from the first available slave through the last. Balance-rr provides load balancing and fault tolerance.

Active Backup (Fail Over) Active Backup uses just one adapter. It switches to the second adapter if the first adapter fails. Only one slave in the bond is active. The bond’s MAC address is only visible externally on one port (network adapter) to avoid confusing the switch. Active Backup mode provides fault tolerance.

Balance XOR Balance XOR balances traffic by splitting up outgoing packets between the adapters, using the same one for each specific destination when possible. It transmits based on the selected transmit hash policy. The default policy is a simple slave count operating on Layer 2 where the source MAC address is coupled with destination MAC address. Alternate transmit policies maybe selected via the xmit_hash_policy option. Balance XOR mode provides load balancing and fault tolerance.
Broadcast Broadcast sends traffic on both interfaces. Balanced XOR mode provides fault tolerance.

IEEE 802.3ad (Dynamic Link Aggregation)
Dynamic Link Aggregation uses a complex algorithm to aggregate adapters by speed and duplex settings. It utilizes all slaves in the active aggregator according to the 802.3ad specification. Dynamic Link Aggregation mode provides load balancing and fault tolerance but requires a switch that supports IEEE 802.3ad with LACP mode properly configured.

Balance-tlb (Adaptive Transmit Load Balancing)
Balance-tlb uses channel bonding that does not require any special switch support. The outgoing traffic is distributed according to the current load on each slave (computed relative to the speed). Incoming traffic is received by the current slave. If the receiving slave fails, the other slave takes over the MAC address of the failed receiving slave. Balance-tlb mode provides load balancing and fault tolerance.

Balance-alb (Adaptive Load Balancing)
Balance-alb is similar to balance-tlb but also attempts attempts to redistribute incoming (receive load balancing) for IPV4 traffic. This setup does not require any special switch support or configuration. The receive load balancing is achieved by ARP negotiation sent by the local system on their way out and overwrites the source hardware address with the unique hardware address of one of the slaves in the bond such that different peers use different hardware address for the server. Balance-rlb mode provides load balancing and fault tolerance.

Network bonding : Part II ( modes of bonding )
The steps for creating network boding in Linux is available in http://unixfoo.blogspot.com/search/label/networking. RHEL bonding supports 7 possible "modes" for bonded interfaces. These modes determine the way in which traffic sent out of the bonded interface is actually dispersed over the real interfaces. Modes 0, 1, and 2 are by far the most commonly used among them.

Mode 0 (balance-rr)
This mode transmits packets in a sequential order from the first available slave through the last. If two real interfaces are slaves in the bond and two packets arrive destined out of the bonded interface the first will be transmitted on the first slave and the second frame will be transmitted on the second slave. The third packet will be sent on the first and so on. This provides load balancing and fault tolerance.

Mode 1 (active-backup)
This mode places one of the interfaces into a backup state and will only make it active if the link is lost by the active interface. Only one slave in the bond is active at an instance of time. A different slave becomes active only when the active slave fails. This mode provides fault tolerance.

Mode 2 (balance-xor)
Transmits based on XOR formula. (Source MAC address is XOR'd with destination MAC address) modula slave count. This selects the same slave for each destination MAC address and provides load balancing and fault tolerance.

Mode 3 (broadcast)
This mode transmits everything on all slave interfaces. This mode is least used (only for specific purpose) and provides only fault tolerance.

Mode 4 (802.3ad)
This mode is known as Dynamic Link Aggregation mode. It creates aggregation groups that share the same speed and duplex settings. This mode requires a switch that supports IEEE 802.3ad Dynamic link.

Mode 5 (balance-tlb)
This is called as Adaptive transmit load balancing. The outgoing traffic is distributed according to the current load and queue on each slave interface. Incoming traffic is received by the current slave.

Mode 6 (balance-alb)
This is Adaptive load balancing mode. This includes balance-tlb + receive load balancing (rlb) for IPV4 traffic. The receive load balancing is achieved by ARP negotiation. The bonding driver intercepts the ARP Replies sent by the server on their way out and overwrites the src hw address with the unique hw address of one of the slaves in the bond such that different clients use different hw addresses for the server.

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