Time To Live.
See [TTL. Time To Live. The amount of time or number of hops a packet is allowed to exist in a network; it prevents packets that are looping from doing so forever.]

Physical layout of a network.

topology table.

A database of reachable destinations used by EIGRP for inserting destinations into the routing table and determining what alternate routes are available.

totally stubby area.

An OSPF area into which no summary routes (type 3 LSAs) or external routes (type 5 LSAs) are advertised.

transit path.

A link in the network over which traffic passes to other areas of the network; transit traffic is not destined to a network attached directly to either end of the path.

transport layer.

The layer in the OSI model that is ...

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