Understanding Linux Network Internals

Interaction with Other Subsystems

The neighboring subsystem interacts with other subsystems, both by generating and by receiving notifications when specific events take place. Here are some of the other subsystems involved in these interactions:

Routing

The relationship between caching at this layer and header caching at the neighbor layer is described in the section "L2 Header Caching."

Traffic equalizer (TEQL)

TEQL is one of Traffic Control's queuing disciplines that can be configured through the IPROUTE2 package's tc command. This feature groups a set of links at the L3 layer and uses them in round-robin fashion when transmitting packets to a given destination. The impact on the neighboring protocol is that the resolution of a single IP address (the master address) may actually trigger the resolution of multiple slave IP addresses.

Because each link in the group has to resolve the L3-L2 address binding, the first round over the devices in the group will need that binding to be resolved when moving from one slave to another.

IPsec

IPsec defines a series of transformations that need to be applied to a packet before it can be transmitted—notably encryption. Because of this, if the effects of IPsec were added to Figure 27-1, it would show multiple dst_entry structures in a linked list, and only the last one would have a pointer to a neighbour structure (see Figure 33-5 in Chapter 33).

Netfilter (iptables)

Netfilter hooks are placed at various points affecting the ingress, egress, ...