Hi Piotr,
I hope this is of some use to you. Here is my input...
First of all by default VIP has ARP unchecked so no ARP replies and not possible to connect from client - why it's default setting?
ICMP should be enabled by default and ARP is disabled. ICMP requires ARP so ARP is enabled regardless of whether the option is checked. I came across this is in the past and I am sure there is a good explanation for it on askF5. Can you ping the VIP IP and if not, maybe worth taking a tcpdump to see what is happening at arp and icmp level.
In what scenario this VS can be reached?
The VIP is reachable if the routing is in place whether you are connecting directly or via a route you defined. Remember the BIG-IP also needs to be able to reach the source host...
Second I tried to access VS using 10.128.80.40 (network) and 10.128.80.47 (broadcast) and still can connect to http server behind LTM. Is that by design? I was pretty sure that net and broadcast IPs would be excluded from host ip range?
Not sure how you have your VIP and self's configured.
Alex