Understanding Linux Network Internals

Data Structures Featured in This Part of the Book

In the section "Main Data Structures" in Chapter 27, we had a brief overview of the main data structures used by the neighboring subsystem. This section presents a detailed description of each data structure's field.

Figure 29-4 shows the files that define each data structure. The ones with a lighter color are not part of the neighboring subsystem, but I referred to them in this part of the book.

Figure 29-4. Distribution of data structures in kernel files

neighbour Structure

Neighbors are represented by struct neighbour structures. The structure is complex and includes status fields, virtual functions to interface with L3 protocols, timers, and cached L2 headers.

Here is a field-by-field description:

struct neighbour *next

Each neighbour entry is inserted in a hash table. next links the structure to the other ones that collide and share the same bucket. Elements are always inserted at the head of the list (see the section "Creating a neighbour Entry," and Figure 27-2 in Chapter 27).

struct neigh_table *tbl

Pointer to the neigh_table structure that defines the protocol associated with this entry. If the neighbor is an IPv4 address, for instance, tbl points to arp_tbl.

struct neigh_parms *parms

Parameters used to tune the neighboring protocol behavior. When a neighbour structure is created, parms is initialized with the values of the default ...