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Forum Discussion
Issues with LACP with VLANs
Hi all,
Network newbie here. I am having some trouble with VLAN's combined with LACP. The setup I have at the moment are purely for educating my self. It consists of:
One Netgear GS724Tv4
One PFsense router virtualized in Proxmox. The LAN interface of router is a separate NIC where all ports are in the same bond, which is configured for LACP. This bond have a dedicated bridge which is assigned as LAN interface for the router. This NIC is connected to port 1-4 on the switch, which is configured as "lag1"
One Synology rack station with a SSD. The LAN interface is configured to use all four ports in LACP. It is connected to ports 5-8 on the switch which is configured as "lag2"
I am using two computers to test the bandwidth of the system, just by simply copying a large file from each computer to the NAS. These are either connected to ports 19 and 20, or 21 and 22 depending on which VLAN I want to use.
When connecting the computers to the same VLAN as the NAS everything seems to work just fine:
Port 19 and 20 are receiving ~2050000 packets each. Lag2, the LACP of the NAS, is transmitting ~4100000 packets. These packages are distributed between port 6 and 8. This means that the LACP to the NAS is working, right?
But when moving the computers to another VLAN the trouble begins:
Port 21 and 22 are receiving ~2050000 packets each. These are transmitted to the router on lag1 and it seems like it decided to use port 2 and 3 for the task.
The router is routing the packages from the VLAN with the computers to the VLAN with the NAS. The switch is receiving the packages on lag1 again, but this time on port 1 and 3.
So far so good? It seems like the LACP between the switch and the router is working good to?
The switch is transmitting the packages on lag2 to the NAS, but why does it only use port 8 now!?
The consequence is obvious when looking at the speeds of the file transfer...
What am I missing?
1 Reply
What am I missing?
LACP is designed so each data flow only runs over one port of the LAG. The traffic for that flow is not split over multiple ports. This approach prevents buffer overruns on the final destination link (which is presumed not to be a LAG).
You have two data flows, so there is a 50-50 chance they will be transmitted on the same port.
In general, LACP does a reasonable job of load balancing when there is traffic from a lot of devices running over the LAG. But as you are finding, the load balancing doesn't perform well if you only have a couple of data flows.
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