Separation of L2/L3-specific Neighbor Data

• Linux has unified data structure for neighbors for various L2/L3 such as:

• L2: Ethernet, Firewire, ATM, …
• L3: IPv4, IPv6, DECnet, …

• In addition to basic state/mapping between L2/L3, it can hold additional data specific to L2 or L3.

• Because the only users (ATM and DECnet) are exclusive (DECnet over ATM is not possible), the code assumes that L2/L3 specific data are not used at the same time.

• Problems

• SEND (Securing Neighbour Discovery) may want to have IPv6-specific data (timestamp, key etc.)
• Firewire or other L2 may want to have L2-specific data
• Even without these, we always calculated size of entry size when allocating new NCE.