HP 800 User Manual page 432

System Administration
Working with Ranges
NOTE:
15-24
When using Extreme switches running ExtremeWare or ExtremeXOS prior
to release 11.6, DHCP relay IP addresses to enforce will NOT work when the
quarantine subnet is a subset of the production network. This is because
Extreme switches forward the packets from the IP address closest to NAC
800 and not the IP address of the interface closest to the endpoint, so all the
DHCPRelay packets will appear to come from a production network IP
address.
For example, the following scenario will not work:
NAC 800 IP: 10.241.88.20
Production Network: 10.241.90.0/24
Quarantine Network: 10.241.90.160/27 (161-189 for range)
Gateway IP: 10.241.90.190
Non-Quarantine Networks: 10.241.90.0/25, 10.241.90.128/27, 10.241.90.192/26