Configuring a device for proxy ARP

Red Hat Enterprise Linux 9.2 LPAR mode z/VM guest

You can configure a device for proxy ARP if the layer2 option is not enabled. If you enabled the layer2 option, you can configure for proxy ARP as you would in a distributed server environment.

Before you begin

Configure only qeth group devices that are set up as routers for proxy ARP.

About this task

The qeth device driver maintains a list of IP addresses for which a qeth group device handles ARP and issues gratuitous ARP packets. For more information about proxy ARP, see 
https://www.cisco.com/c/en/us/support/docs/ip/dynamic-address-allocation-resolution/13718-5.html

Use the qethconf command to display this list or to change the list by adding and removing IP addresses.

Be aware of the information in Confirming that an IP address has been set under layer 3 when you work with proxy ARP.

Example

Figure 1 shows an environment where proxy ARP is used.
Figure 1. Example of proxy ARP usage
This graphic is described in the text that follows.

G1, G2, and G3 are instances of Linux® on z/VM® (connected, for example, through a guest LAN to a Linux router R), reached from GW (or the outside world) through R. R is the ARP proxy for G1, G2, and G3. That is, R agrees to take care of packets that are destined for G1, G2, and G3. The advantage of using proxy ARP is that GW does not need to know that G1, G2, and G3 are behind a router.

To receive packets for 1.2.3.4, so that it can forward them to G1 1.2.3.4, R would add 1.2.3.4 to its list of IP addresses for proxy ARP for the interface that connects it to the OSA adapter. 
# qethconf parp add 1.2.3.4 encf500
qethconf: Added 1.2.3.4 to /sys/class/net/encf500/device/rxip/add4.
qethconf: Use "qethconf parp list" to check for the result
After issuing similar commands for the IP addresses 1.2.3.5 and 1.2.3.6 the proxy ARP configuration of R would be: 
# qethconf parp list
parp add 1.2.3.4 encf500
parp add 1.2.3.5 encf500
parp add 1.2.3.6 encf500