1. Straight-through cable (39-40): connects the wire at pin 1 on one end of the cable to pin 1 at the other end of the cable; the wire at pin 2 needs to connect to pin 2 on the other end of the cable; pin 3 on one end connects to pin 3 on the other; and so on. (To create a straight-through cable, both ends of the cable use the same TIA pinout standard on each end of the cable.) Crossover cable: a cable that swaps the wire pairs inside the cable
2. Collision domain (43): the set of devices whose frames could collide; switches increase the size and number of collision domains
3. IPv4 Header Fields (98)
Version: Version of the IP protocol. Most networks use version 4 today. TTL: Time to live. A value used to prevent routing loops.
Header Checksum: A value used to store an FCS value, whose purpose is to determine if any bit errors occurred in the IP header. Source IP address: The 32-bit IP address of the sender of the packet. Destination IP address: The 32-bit IP address of the intended recipient of the packet.
4. Passive-interface (342): stops the sending of RIP updates on the interface
5. Classless and Classful Routing (454): For a routing protocol to support VLSM, the routing protocol must advertise not only the subnet number but also the subnet mask when advertising routes. Additionally, a routing protocol must include subnet masks in its routing updates to support manual route summarization.
6. Overlapping VLSM Subnets (455): The subnets chosen to be used in any IP internetwork design must not overlap their address ranges. With a single subnet mask in a network, the overlaps are somewhat obvious; however, with VLSM, the overlapping subnets might not be as obvious. When multiple subnets overlap, a router’s routing table entries overlap. As a result, routing becomes unpredictable, and some hosts can be reached from only particular parts of the internetwork. In short, a design that uses overlapping subnets is considered to be an incorrect design, and should not be used.
7. Manual Route Summarization (461): Route summarization reduces the size of routing tables while maintaining routes to all the destinations in the network. As a result, routing performance can be improved and memory can be saved inside each router. Summarization also improves convergence time, because the router that summarizes the route no longer has to announce any changes to the status of the individual subnets. The term manual refers to the fact that manual route summarization only occurs when an engineer configures one or more commands. Summary routes, which replace multiple routes, must be configured by a network engineer.
8. ICMP Unreachable Codes (479)
Network unreachable: There is no match in a routing table for the packet’s destination. Host unreachable: The packet can be routed to a router connected to the destination subnet, but the host is not responding. Can’t fragment: The packet has the Don’t Fragment bit set, and a router must fragment to forward the packet. Protocol unreachable: The packet is delivered to the destination host, but the transport layer protocol is not running on that host. Port unreachable: The packet is delivered to the destination host, but the destination port has not been opened by an application.
9. The ICMP Time Exceeded Message (481): The ICMP Time Exceeded message notifies a host when a packet it sent has been discarded because it was “out of time.” Packets are not actually timed, but to prevent them from being forwarded forever when there is a routing loop, each IP header uses a Time to Live (TTL) field. Routers decrement the TTL by 1 every time they forward a packet; if a router decrements the TTL to 0, it throws away the packet.
10. Open Shortest Path First (OSPF) (506): the most popular link-state IP routing protocol
11. Dijkstra Shortest Path First (SPF) algorithm (507): The SPF algorithm can be compared to how humans think when taking a trip using a road map. Anyone can buy the...
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