Peace be upon those who follow guidance,

I found it simple to share internet between fedora 29 and windows vista via LAN by using the following:

1. Run nm-connection-editor
2. Add new connection
3. In IPv4 setting set method to Shared with other devices
4. MAC address set to stable

if you have a router or switch you can use straight cable and connect these two machines, if you do not have either then you can use cross cable to connect .

do the following on the Linux box on using which you are connected to Internet

Flush all the present rules

iptables -F

iptables -t nat -F

iptables -t mangle -F

Delete any rules you have

iptables -X

iptables -t nat -X

iptables -t mangle -X

service iptables save

service iptables restart

enable packet forwarding

echo "1" > /proc/sys/net/ipv4/ip_forward

to make this change permanent you can copy the above line in /etc/rc.d/rc.local

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

service iptables save

service iptables restart

now try to browse using the xp laptop , be sure they are in same subnet and routing tables is pointing to the linux box.