US Robotics USR2410 Manuel d'utilisateur télécharger pdf (Page 31)

Chapter 5 -

Packet Routing: Click Modular Router

The Click Modular Router was responsible for defining how each mesh router would route

packets throughout the system. Packets are sent from Click to the network driver, a

communication device connected to the host router, or the Linux kernel of the host system its self.

Designed to be flexible and configurable, Click uses a number of routing elements each

performing a different operation on a packet. Packets flow through these elements, eventually

reaching their output destination.

Section one of this chapter will discuss the important Click elements used in the project’s router

configuration files. The implementation of the DSDV Routing Protocol and the relevant click

elements used in its configuration are presented in section two. The packet flow through the

complete routing system implementing both Click and DSDV elements is shown in section 3.

5.1

Click Elements

The following section will discuss four configurable Click elements used in the project’s router

configuration files. The processing preformed by these elements is described in the following

sections. Most elements did not require specific configuration. For a description of the other

elements included in the configuration files, see Appendix A.

5.1.1

IPRewriter

This element was used to perform NAT on TCP and UDP packets. This section describes the

address translation scheme used by the IPRewriter. Then, the addressing patterns used in the

network are described. The reverse flow case is shown, and then finally the inputs and outputs of

the element are described.

The element created a mapping based on a packet flow identifier. This was a set containing the

source address, source port, destination address, destination port and protocol of the packet. The

packet flows were mapped based on patterns to change source IP address and source port of the

packet requiring network address translation. The IPRewriter elements implemented in the

configurations used in the mesh network had the same format for each pattern. They changed the

source IP address to be that of the host router, and assigned the flow a source port on that router

in the range of 50000-65535. The destination IP address and port were left unchanged. A special

pattern named ‘pass’ was also used; it did not modify any parameters of the flow identifier. The

IPRewriter element kept track of the packet flows for packets that were input. If no previous

mapping existed, a new one was created. If a previous mapping existed, the packet’s addresses

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US Robotics USR2410 Manuel d'utilisateur Page 31