US Robotics USR2410 Instrukcja Użytkownika Pobierz pdf (Strona 58)

Appe ndix A -

Click Elements

Classifier

This element, along with the IPClassifier, formed the basis of how packets flowed through the

click router. It classified all the input packets based on an offset, and a bit value. Each of these

patterns had an associated output. If a packet matches the bit value at the given offset, they were

sent out the corresponding output. A special pattern, ‘-‘, matched every packet, and could be used

as the last pattern in order to route all unmatched packets. This element formed a construct

similar to many programming languages switch/case statement.

IPClassifier

This element functioned in the same manner as the Classifier, except that it classified packets

based on their type, or the protocol they used. For example, it could distinguish echo-request

ICMP packets from ICMP error packets. It could also classify packets based on their destination

or source IP addresses.

ARPQuerier

This element was used to discover system MAC addresses using the ARP protocol. It contained a

table of MAC addresses associated with IP addresses. If a packet arrives on input 0, and there is

no mapping, an ARP request is sent out. When the ARP reply arrived on input 1, the table was

updated and the packet was sent out.

GetIPAddress

This element sets the destination IP address annotation.

CheckIPHeader

This element checks the integrity of the IP header of a packet. It also sets the destination IP

address annotation for that packet.

TTLChecker - Compound Element

This compound element was used to decrement the time to live (TTL) for a packet if it was being

forwarded to another router. Classifiers were used to decrement only the TTL for IP packets that

did not originated from the host router. All other packets were just sent to the output. The TTL is

decremented using the DecIPTTL element. If it had not expired, the checksum for the packet was

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US Robotics USR2410 Instrukcja Użytkownika Strona 58