link aggregation

[VJ]

Hello,

In which scenarios do you benefit from "link aggregation" on a switch?
Obviously, in this situation, where both devices are connected with a dual link:

computer == switch == computer

But what about this one (one device connected with an aggregated link, two other devices connected with a single link)?

computer == switch -- computer
                  '-- computer

Thanks!

Jörg

[Evildead666]

It should only go as fast as the slowest part of the setup.
The switch will be GBe, so 1GBps should be the fastest you can go, single or dual link network.
Dual link could mean that one is used for upstream, and one for downstream, or for fall-back purposes when one link goes down for some reason.

I don't think you can sustain a 2GBps link through a 1GBps switch, even using two ports, since it is a 'switch' ie it will route packets as fast as it can go, but you can't add the port speeds up.

[VJ]

And if you have a switch that supports aggregation (802.1ad, LACP, e.g. D-Link DGS 1210 series: ftp://ftp.dlink.eu/datasheets/DGS-1210-16.pdf )?

The documentation I found seems to say that you can increase bandwith between things (e.g. the first scenario, it will not be double, but it will be close) but to me it was unclear if you also benefit from an increased bandwith in the second scenario I drew (both computers receiving full speed rather than 50% of the bandwith).

http://en.wikipedia.org/wiki/Link_aggregation

http://www.intel.com/support/network/sb/cs-009747.htm

[VJ]

I think I found the answer in this paper:

http://legacyweb.triumf.ca/canarie/amsterdam-test/References/wp-lag-e.pdf

Load sharing
MAC Client traffic may be distributed across multiple links.

Backwards compatibility with aggregation-unaware devices
Links that cannot take part in Link Aggregation - either because of their inherent capabilities,
management configuration, or the capabilities of the devices to which they attach
– operate as normal, individual IEEE 802.3 links.

So this seems to tell me that there also is a benefit in the second scenario... Can anyone confirm?

Thanks!

[VJ]

Slightly off topic: the difference in MTBF in the different D-Link 1210 models is startling: from 200000 hours for the 10 port model, to 800000 hours for the 16 port model, and then 410000 and 320000 for the other two models... Weird... (ok, the 10 port model has PoE, what the others don't have, so that might explain this one; but the other three...)

[VJ]

My system administrator confirmed that if the switch supports link aggregation, you will benefit in the scenario where 2 computer connected via a single link communicate simultaneously to one that is connecting using 2 teamed links.

As there was I a good price on it, I went and ordered the DGS-1210-16.
I have about 14 ports in the apartment, and there are some left on the router as well (16 on switch +4 on router - 2 to connect both = 18 available ports). So there even is room to add a NAS next to the switch. And in the unlikely event I use ALL the ports; I can always add a second small switch.

The order has been placed, but now I just come to realize it is not on the D-Link IPv6 list. But I'm not sure this is a problem: the only items there are mainly routers and some very high end switches... And I think my windows can communicate using IPv6 through my 8 year old linksys router...

[Jammrock]

Your NICs have to support it and you need "teaming" software to set it up on the server, too. Cisco has a new tech called Virtual Port Connection (VPC). It allows you to have a teamed/aggregate connection across two separate switches for true port redundancy. Only available on the Nexus line afaik.

[VJ]

Most NAS with 2 ports support teaming, and most mainboards that have two nics of the same vendor (2x intel, 2x realtek, ...) also usually support it. So it makes sense to have a switch that supports it (in its web interface you should indicate which ports are teamed): I intend to stream full hd video, and this will allow me for sure to stream to multiple sources.

[dZeus]

what kind of full HD video.... raw format? because full HD video like bluray is peanuts for a single gigabit lan link. Max bitrate is 40 Mbps, and gigabit ethernet should easily do at least 10 to 20 times that.

[VJ]

I know, but if the switch is the only component preventing teaming, and I found a good deal on a switch that supports it, why not go for it? More network bandwidth is always welcome.

[dZeus]

why not throw in some RAID0 too for extra bandwidth while you're at it?

[Jammrock]

why not throw in some RAID0 too for extra bandwidth while you're at it?

RAID 0 with SSDs or you'll never saturate a teamed Gbps pair.

[VJ]

Haha... guys... I needed a switch, have devices that support teaming, and found a nice deal on a switch that supports it. Tell me you would not go for it?

Just: how would it go with IPv6?
I know I have pinged computers via IPv6 over my old router/switch, so will it work? Or will some tunneling (6to4) would have to be done?

[Jammrock]

I honestly don't know. I guess it depends on the teaming software and how you set it up.