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ARP caches the mapping of IP IPv4 addresses to physical (i.e., MAC) addresses. NET_ARP_CFG_NBR_CACHE configures the number of ARP cache entries. Each cache entry requires approximately 18 bytes of RAM, plus five seven pointers, plus a hardware address and protocol address (10 bytes assuming Ethernet interfaces and IPv4 addresses).
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NDP is only used when the IPv6 stack is enabled.
NDP caches the mapping of IPv6 addresses to physical (i.e., MAC) addresses. NET_NDP_CFG_NBR_CACHE configures the number of NDP Neighbor cache entries. Each cache entry requires approximately 18 bytes of RAM, plus seven pointers, plus a hardware address and protocol address (22 bytes assuming Ethernet interfaces and IPv6 addresses).
NDP also caches recent IPv6 destination addresses by mapping next-hop address to final destination address. It allows the µC/TCP-IP stack not having to re-calculating the next-hop for each packet to send. NET_NDP_CFG_DEST_NBR configured the numver of NDP destination caches available for the TCPIP stack.
In IPv6, routers send router advertisement messages to inform hosts on different values like the IPv6 prefix considered on-link. Those on-link prefix are stored in a NDP prefix list. NET_NDP_CFG_PREFIX_NBR configured the the number of prefix entries available in the list.
IPv6 defines an algorithm to chose the adequate router on the network to transmit packet outside in case more than one IPv6 router is present. NET_NDP_CFG_ROUTER_NBR defines the number of router information that can be store by the µC/TCP-IP stack.
IPv4 Layer Configuration
IPv6 Layer Configuration
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