Make synergy work between qemu host and guest

I have a working configuration of a Gentoo as a host and a Windows 10 as a guest using QEMU/KVM with GPU passthrough. I also passthrough my keyboard and mouse, and have a secondary keyboard in a different USB port, which is used by the host. I have installed Synergy on both operating systems, but even thought they share the same IP, I can't get them to see each other with "localhost". I have read that I should rather use bridges, or tun-tap devices, but I can't really understand what they do and would like a bit of help setting them up. Finally, here is my qemu startup script: #!/bin/bash rm /tmp/my_vars.fd cp /usr/share/edk2.git/ovmf-x64/OVMF_VARS-pure-efi.fd /tmp/my_vars.fd export QEMU_AUDIO_DRV=pa QEMU_PA_SAMPLES=8192 QEMU_PA_SERVER=127.0.0.1 qemu-system-x86_64 \ -enable-kvm \ -m 6144 \ -smp cores=4,threads=1 \ -soundhw hda \ -usb -device usb-host,hostbus=1,hostaddr=3 \ -usb -device usb-host,hostbus=1,hostaddr=4 \ -device vfio-pci,host=01:00.0,multifunction=on \ -device vfio-pci,host=01:00.1 \ -drive if=pflash,format=raw,readonly,file=/usr/share/edk2.git/ovmf-x64/OVMF_CODE-pure-efi.fd -device virtio-scsi-pci,id=scsi \ -drive file=/dev/sda5,id=disk,format=raw,if=none -device scsi-hd,drive=disk