Diagnostic Terms

Before diagnosing your device, become familiar with the terms defined in Table 144.

Table 144: Diagnostic Terms

Term	Definition
Don't Fragment (DF) bit	Bit in the IP header that instructs routers not to fragment a packet. You might set this bit if the destination host cannot reassemble the packet or if you want to test the path maximum transmission unit (MTU) for a destination host.
routing instance	Collection of routing tables, interfaces, and routing protocol interfaces. The set of interfaces belongs to the routing tables, and the routing protocol parameters control the information in the routing tables.
loose source routing	Option in the IP header used to route a packet based on information supplied by the source. A gateway or host must route the packet using the routers specified by this information, but the packet can use other routers along the way.
strict source routing	Option in the IP header used to route a packet based on information supplied by the source. A gateway or host must route the packet exactly as specified by this information.
time to live (TTL)	Value (octet) in the IP header that is (usually) decremented by 1 for each hop the packet passes through. If the field reaches zero, the packet is discarded and a corresponding error message is sent to the source of the packet.
type of service (TOS)	Value (octet) in the IP header that defines the service the source host requests, such as the packet's priority and the preferred delay, throughput, and reliability.