Link aggregation
Other umbrella terms used to describe the concept include trunking,[1] bundling,[2] bonding,[1] channeling[3] or teaming.
Multiple logical connections can be made, but many of the higher level protocols were not designed to fail over completely seamlessly.
OSI layer 2 (data link layer, e.g. Ethernet frame in LANs or multi-link PPP in WANs, Ethernet MAC address) aggregation typically occurs across switch ports, which can be either physical ports or virtual ones managed by an operating system.
[4] The group quickly agreed to include an automatic configuration feature which would add in redundancy as well.
The 802.3 maintenance task force report for the 9th revision project in November 2006 noted that certain 802.1 layers (such as 802.1X security) were positioned in the protocol stack below link aggregation which was defined as an 802.3 sublayer.
[6] To resolve this discrepancy, the 802.3ax (802.1AX) task force was formed,[7] resulting in the formal transfer of the protocol to the 802.1 group with the publication of IEEE 802.1AX-2008 on 3 November 2008.
Software-based implementations – such as the *BSD lagg package, Linux bonding driver, Solaris dladm aggr, etc.
They may be given as command-line arguments to the insmod or modprobe commands, but are usually specified in a Linux distribution-specific configuration file.
Link aggregation offers an inexpensive way to set up a high-capacity backbone network that transfers multiple times more data than any single port or device can deliver.
Common implementations use L2 or L3 hashes (i.e. based on the MAC or the IP addresses), ensuring that the same flow is always sent via the same physical link.
For this reason, an even load balancing and full utilization of all trunked links is almost never reached in real-life implementations.
For example, this allows a central file server to establish an aggregate 2-gigabit connection using two 1-gigabit NICs teamed together.
Note the data signaling rate will still be 1 Gbit/s, which can be misleading depending on methodologies used to test throughput after link aggregation is employed.
Previous Windows Server versions relied on manufacturer support of the feature within their device driver software.
HP has a teaming tool for HP-branded NICs which supports several modes of link aggregation including 802.3ad with LACP.
In addition, there is a basic layer-3 aggregation[22] that allows servers with multiple IP interfaces on the same network to perform load balancing, and for home users with more than one internet connection, to increase connection speed by sharing the load on all interfaces.
[24] Linux, FreeBSD, NetBSD, OpenBSD, macOS, OpenSolaris and commercial Unix distributions such as AIX implement Ethernet bonding at a higher level and, as long as the NIC is supported by the kernel, can deal with NICs from different manufacturers or using different drivers.
vSphere 5.1 (ESXi) supports both static LAGs and LACP natively with their virtual distributed switch.
[25] Microsoft's Hyper-V does not offer link aggregation support from the hypervisor level, but the above-mentioned methods for teaming under Windows apply to Hyper-V. With the modes balance-rr, balance-xor, broadcast and 802.3ad, all physical ports in the link aggregation group must reside on the same logical switch, which, in most common scenarios, will leave a single point of failure when the physical switch to which all links are connected goes offline.
But after failover (like all other modes), in some cases, active sessions may fail (due to ARP problems) and have to be restarted.
On Ethernet interfaces, channel bonding requires assistance from both the Ethernet switch and the host computer's operating system, which must stripe the delivery of frames across the network interfaces in the same manner that I/O is striped across disks in a RAID 0 array.
[citation needed] Under the DOCSIS 3.0 and 3.1 specifications for data over cable TV systems, multiple channels may be bonded.
DOCSIS 3.1 defines more complicated arrangements involving aggregation at the level of subcarriers and larger notional channels.
Other bonding methodologies reside at lower OSI layers, requiring coordination with telecommunications companies for implementation.
