RFC 4861 describes the use of the (R) or ‟Router” flag in NA messages as follows:
a node capable of routing IPv6 packets must reply to NS messages with NA messages where the R flag is set (R=1)
hosts must reply with NA messages where R=0
The use of the R flag in NA messages impacts how the hosts select their default gateways when sending packets ‟off-link”. Therefore, it is important that the proxy-ND function on the 7210 SAS meet one of the following criteria:
provide the appropriate R flag information in proxy-ND NA replies
flood the received NA messages if it cannot provide the appropriate R flag when replying
Because of the use of the R flag, the procedure for learning proxy-ND entries and replying to NS messages differs from the procedures for proxy-ARP in IPv4: the router or host flag is added to each entry, and that determines the flag to use when responding to a NS.