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Rikeri53pehi
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CSS610-8G-2S+IN LACP LAG to Synology NAS not working

Sat Feb 27, 2021 2:17 pm

Greetings,

I’m a home user with a simplistic network. I’m trying to set up a 2-port/1Gbit LACP LAG between a CSS610-8G-2S+IN and a Synology DS620slim NAS. When attempting to transfer a 10 GB file from the NAS to two different computers at the same time, only one port is ever utilised on the switch, thus capping my speed at 1 Gbps.
However, if I set the Synology NAS to use Adaptive Load Balancing, I am able to utilise both ports, thus giving me a transfer rate of 2 Gbps.

What could be the reason for LACP not utilising both ports on my switch/NAS?

This is my simple network:

EdgeRouterX: (192.168.1.1)
Synology NAS: (192.168.1.3)
Mac Mini A: (192.168.1.4)
Mac Mini B: (192.168.1.5)
CSS610-8G-2S+IN: (192.168.1.50)

I’m not using VLANs and my devices have all statically assigned IP’s on the same subnet.

The switch is running the latest release candidate: 2.13rc25

In SwOS I have set the LAG mode to “active” for ports 7 and 8 and in the “Trunk” column I can see a number “1" and the “Partner” column shows two identical MAC addresses when I enable LACP on the NAS.

In Synology DSM, the “Network Status” shows “2000 Mbps, Full duplex, MTU 1500".

On the surface, everything appears correct, so what am I missing or have a misunderstood how LACP works? For now I will just have to stick with “Adaptive Load Balancing" which seems to give me the full transfer speed.

Thank you
 
bradfa
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Re: CSS610-8G-2S+IN LACP LAG to Synology NAS not working

Fri Mar 05, 2021 4:02 pm

Can you try the older 2.13rc12 firmware instead? Search the forum to find the box.com download links. There's a few found issues already with the 2.13rc25 firmware which have been resolved for me by going back to the 2.13rc12 firmware.
 
Rikeri53pehi
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Re: CSS610-8G-2S+IN LACP LAG to Synology NAS not working

Mon Mar 08, 2021 11:59 pm

Thank you.
I've tested 2.13rc12 for a couple days now, but there is still no difference in speed. Whatever I do, only one port is ever utilised.
I'll continue to wait for the time being until we have an update to rc25...
 
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mkx
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Re: CSS610-8G-2S+IN LACP LAG to Synology NAS not working

Tue Mar 09, 2021 9:14 am

It seems that SwOS only supports LACP load balancing based on Layer2 and Layer3 hashing. Which means that single client (same MAC and IP address) will always use single connection towards NAS even if running multiple simultaneous transfers (which may differ on L4 - TCP port number).
While statistically L2 / L3 hash will evenly spread (large number of) clients over all available links, with only two clients statistically there's 50% chance both clients will be using same link (either using link1 - client1 has 50% chance of using it, client 2 has 50% chance of using it, there's 25% chance both will be using link1 ... ditto for link2, hence 50% chance both clients will use either link1 or link2 at the same time).
What you can do is to change IP of one of clients (change last octet by 1) and see if this helps. I don't know how particular hashing algorithm works in SwOS, but chances are that changing IP address by 1 will make SwOS select different link for that client.

BTW, it's always transmitting party which selects which particular link will be used for every single ethernet frame. The other party will simply receive it regardless the link selection algorithm in use. Hence both peers can use different algorithms (e.g. one layer-2, the other layer-3-and-4) and LACP bond will still work, although differently in each direction.
BTW2: hash policy layer-2 and layer2-and-3 are only different when one of hosts (client, server) has multiple IP addresses. In normal networks this is only true when clients are behind the router in which case there will be plenty of client IP addresses (L3) in use but always router's MAC address (L2). If both clients and server are members of same IP subnet, then both mentioned hash policies are behaving exactly the same.

There are other strategies of using individual links in LACP, ROS has "transmit-hash-policy=layer-3-and-4" which helps spreading parallel connections between same client and server ... and this in turn helps spread load over all available links more evenly (but if using two connections in parallel, either single client with two connections or two clients with single connection each, there's still 50% chance both will be using same link).

In short: there's no way single connection using both links and there's always chance multiple connections using same link.
 
Rikeri53pehi
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Re: CSS610-8G-2S+IN LACP LAG to Synology NAS not working

Tue Mar 09, 2021 2:20 pm

Thank you very much for this in-depth answer. It all makes much more sense to me now.

I wanted to try your suggestion of "changing the last octet" for one of my client devices.
As I already mentioned in my first post, the last octets on my two devices already have different IPs':

Mac Mini A: (192.168.1.4)
Mac Mini B: (192.168.1.5)

Is that what you meant by "changing the last octet" or did you mean that I should try putting them on different subnets? I.e. 192.168.1.4, 192.168.2.5?

In any case, I get now that by having only two devices that concurrently try to fetch large files off a NAS, there is always a 50% chance that both devices will still use the same port.
I guess I would need to expand my empire to 5+ devices to really see if it works. :)
 
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mkx
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Re: CSS610-8G-2S+IN LACP LAG to Synology NAS not working

Tue Mar 09, 2021 11:48 pm

What I meant was to change e.g. 192.168.1.5 to 192.168.1.6 and see if it uses same link. But then:
... I get now that by having only two devices that concurrently try to fetch large files off a NAS ...
Since in this case SAN is the transmitting party (files being sent by SAN towards PCs), transmit hash policy setting on switch doesn't matter, it's SAN who decides which link to use. You probably should study SAN's documentation to see if its transmit policy is explained and how does it work...
 
Rikeri53pehi
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Re: CSS610-8G-2S+IN LACP LAG to Synology NAS not working

Wed Mar 10, 2021 4:56 pm

Thanks for the tip! I never realised that was the case.
I will do some investigation on the Synology side to see if I can find some information about their transmit policy.
 
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mkx
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Re: CSS610-8G-2S+IN LACP LAG to Synology NAS not working

Thu Mar 11, 2021 12:08 am

I googled a bit and stumbled across this document. It doesn't go into much detail, but in short it says not to use "Adaptive Load Balancing" if you have a switch that knows what link bonding is. I guess the safest choice would be to use 802.3ad bonding.

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