On Carrier Gbit Ethernet - ETH1

First, make sure your VAR-SOM-AM43 device supports ETH1. Please follow the instructions below:
1) Build the correct DTB that supports ETH1 port and replace it on the SD-Card:

make -j6 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- var-som-am43-eth1.dtb
sudo cp arch/arm/boot/dts/var-som-am43-eth1.dtb /media/rootfs/boot/var-som-am43.dtb
sync
sudo umount /media/boot/
sudo umount /media/rootfs
sudo umount /media/user

2) Then, activate the ETH1 device and acquire IP for testing. On Target:

$ ifconfig eth0 down
$ ifconfig eth1 up
$ udhcpc -i eth1
$ ifconfig 
$ iperf -s -u

On Host:

$ iperf -c 192.168.1.82 -u -b450M

VAR-SOM-AM43 GBIT Ethernet

On Carrier Gbit Ethernet - ETH1