US Robotics USR2410 Manual de usuario descargar pdf (Pagina 41)

remotely to the router and wanted to connect to another router. The elements included are shown

in Figure 5-7.

Figure 5-7: Directed Graph of Router Input Processing and Packet Classification Block

The packets from the router were first classified as either ARP request packets, or data. If they

were an ARP request, a reply was sent back to the router itself. This was done since the DSDV

protocol was used to determine the destination of the packet, not the ARP protocol. This is

explained in further detail in the next section.

If the packets were data packets, the Ethernet header was stripped. The IP header was then

checked for integrity. If there was an error, the packet was dropped. If not, the destination IP

address annotation was set for the packet, and it was sent to the ip_demux IPClassifier.

5.3.4.5.

Router Output Processing

This simple block processed packets that were destined for the host router. The elements

included in this block are shown in Figure 5-8.

Figure 5-8: Directed Graph of Router Output Processing Block

In the previous section packets classified as ARP requests were sent to the ARPResponder

element. This element creates a response to the request using a fake MAC address, so that the

Linux kernel would think it had located the machine it was looking for. It would then send out the

packets to that machine, so the packets would be sent out with an Ethernet header containing the

fake address. This header would be stripped in the Router Input Processing and Packet

Classification step.

The EtherEncap element encapsulated the incoming packets in an Ethernet header, using a fake

MAC address. This did no harm, since the packets were then sent to the Linux kernel, where this

Ethernet header was stripped.

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US Robotics USR2410 Manual de usuario Pagina 41