Understanding communication between hosts on the same subnet

Hi All,

 

 

I'm trying to get my head around when to use an irule with snat between hosts on the same subnet.

 

 

For example:

 

 

I have three hosts:

 

 

A = 10.10.10.1/24 (node on F5 / inside vlan)

 

B = 10.10.10.2/24 (node on F5 / inside vlan)

 

C = 10.10.10.3/24 (machine on the outside / outside vlan)

 

 

C wants to talk with A and B directly.

 

 

1/ In this example, do I need to configure a FORWARDING_VIP for C to be able to talk to A and B:

 

 

Set up FORWARDING_VIP for network 10.10.10.0/24

 

(Forwarding IP / All Ports / All Protocols)

 

 

Apply iRule to FORWARDING_VIP to snat hosts on the outside on the same subnet.

 

when LB_SELECTED { if {[IP::addr "[IP::client_addr]/24" equals "[LB::server addr]/24"]} { snat automap } }

 

 

Set up SELF_IP = 10.10.10.4/24

 

Set Default Gateway of A and B set to SELF_IP

 

 

2/ OR because they are all on the same segment, they should be able to ARP for each other's mac address and communicate at layer 2 so no routing involved???

 

 

We've been using option 1 in production for hosts on the same subnet to communicate with each other but now I'm not sure why it's needed (although it's working fine).

 

 

I would think hosts on the outside should be able to arp for hosts on the inside at layer 2 w/o any routing - so is the iRule needed? Yeah and I'm confused.

 

 

Thanks.

 

 

Andy