Odd NFS client behaviour

Alex Atkin UK · August 19, 2019

I have two interfaces on my NAS, 192.168.1.253 which is on the LAN and 192.168.192.253 which is directly connected to my desktop.
My desktop has 192.168.1.1 assigned by DHCP on a 2.5Gbit NIC and 192.168.192.1 static IP on its on-board gigabit connected to the NAS.

I was originally going to use NFS multipathing to combine both links but there is so little documentation on it, I couldn't figure out how to do it.
So as an alternative I decided to try mounting one of my shares on the Gigabit link instead of the LAN.

Server: /etc/exports

/home/alexatkin            192.168.1.1(rw,no_subtree_check)
/home/newsbin              192.168.1.1(rw,no_subtree_check,all_squash,anonuid=1002,anongid=100)  192.168.192.1(rw,no_subtree_check,all_squash,anonuid=1002,anongid=100)

Client: /etc/fstab

server:/home/alexatkin           /home/alexatkin/Server/Documents nfs4 noatime,bg,tcp,actimeo=1800 0 0
192.168.192.253:/home/newsbin    /home/alexatkin/Server/Newsbin nfs4 noatime,bg,tcp,actimeo=1800 0 0

But NFS for some bizarre reason is mounting the second entry like this:

server:/home/newsbin on /home/alexatkin/Server/Newsbin type nfs4 (rw,noatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,acregmin=1800,acregmax=1800,acdirmin=1800,acdirmax=1800,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.1.1,local_lock=none,addr=192.168.1.253)

Even if NFS has realised its the same NFS server, why would it ignore my explicit instruction to mount by a specific IP address? That IP address is not in DNS, it does not resolve to server.

What's even more puzzling is the client routing table shows:

Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         Router.lan      0.0.0.0         UG    101    0        0 enp1s0f2u1
192.168.1.0     0.0.0.0         255.255.255.0   U     101    0        0 enp1s0f2u1
192.168.122.0   0.0.0.0         255.255.255.0   U     0      0        0 virbr0
192.168.192.0   0.0.0.0         255.255.255.0   U     100    0        0 enp0s31f6

So surely it should prioritise 192.168.192.253 anyway if it knows there are multiple paths to the server?
If I run iperf3 or ping to 192.168.192.253, it goes over the correct interface. Why is NFS behaving differently?

I could probably remove the export for that share over the LAN as its not needed, but I really want to know why NFS is behaving like this as I may wish to do it with other shares which ARE shared to the whole LAN.

Worth noting is I did used to mount this share using the server:path but both client and server has been rebooted since then so it shouldn't be remembering that session.