Synology DS920+ and Cisco CBS350 link aggregation

For home use, link aggregation does not have many benefits. With my current network topology (2 VLANs), it would probably make more sense to connect one link to VLAN 10 and second link to VLAN 20, as this is simpler approach and for most time will serve the same purpose – Traffic from backups or heavy traffic transfer in server VLAN should not cause issues in VLAN 20, where home clients are.

However setting up link aggregation, does allow me to play around with it and offers more flexibility in future if I need it – NAS has only one IP and I let network appliances handle how to get there. It also gives me some redundancy, if one link fails the file transfer should still complete.

Cisco CBS 350 configuration

I will be using interface 15 and 16 for this. They are currently set up as vlan 10 access ports. At this stage, Synology NAS is connected to a different port.

First I remove the vlan 10 from individual interfaces

conf t 
interface GigabitEthernet15
no switchport access vlan
interface GigabitEthernet16
no switchport access vlan

Now I will set up load balancing. I did not find concrete proof on the Internet which load balancing would be better: src-dst-mac or src-dest-mac-ip, as „it depends” but src-dst-mac is usually the worst. In that case I decied to go with src-dest-mac-ip first and change it in future if there is an issue.

conf t 
port-channel load-balance src-dst-mac-ip
no negotiation
interface range GigabitEthernet15-16
no negotiation

and

channel-group 1 mode auto
interface port-channel 1 
flowcontrol on
descritpion LAG_NAS

Then I set it as access ports

switchport access vlan 10

The result is configuration as below.

Now it’s time for LACP configuration. I decided to set it in fast configuration, as it enables faster detection of faults. It will send LACP PDU every second, which won’t be an issue in my environment (and probably most other environments).

configure
interface range GigabitEthernet15-16
lacp port-priority 1 
lacp timeout short
exit

The switch should be ready. For more step by step you can also check cisco docs, from which most of the steps were take from. Link is here.

Synology DS920+ configuration

At this moment only one Ethernet port is used. After the configuration is done I will plug both into port 15 and 16 on my switch.

First I started with backing up my current config. This can be found in Control Panel -> Updates & Restore -> Manual Export

After config files were exported it’s time to bond the Ethernet ports.

In Control Panel -> Network -> Network Interface click Create -> Create New Bond

Since Cisco CBS 350 supports link aggregation I chose the second option.

Next the Ipv4 section

I decided to go with DHCP option, as I try to move away from static IPs. I had DHCP set up before. After setting up bonding, the IP address stayed the same.

I left „set as default gateway and MTU value unset.

As for Enabling VLAN (802.1Q) option, I’ve looked extensively on the Internet on the advantages of configuring VLANs on Synology with connecting via SSH and editing config files and using trunk port on switch. However I am not sure what advantages there are over connecting the NAS to access port and letting the switch and Firewall handle the VLAN traffic.

With InterVlan routing done on Cisco CBS350 for my LAN networks, devices in both Vlan 10 and 20 can access NAS.

I can also confirm that LACP is working and removing 1 ethernet cable from NAS does not stop the file transfer.

The total transfer also increased, so it seems to be working as expected.

I connected to the switch and saved config with command:

wr

Thanks for reading.