CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

MISC Data Link Layer Notes
- Ethernet is an example of connectionless networks, which means that the destination end
systems are not contacted prior to communication, nor is there any mechanism for the sender to
know whether a frame has reached its intended destination.
- Every time a transparent bridge learns a MAC address, it would timestamp the entry.
When the bridge sees a frame from this MAC address, it refreshes the timestamp. If the bridge
does not hear from this source for a specific amount of time (aging timer), the bridge deletes the
entry from its bridging table. The default MAC address table aging timer is 5 minutes.
- Content-Addressable Memory (CAM) is a special type of computer memory that implements
the lookup-table function in a single clock cycle (single operation) using dedicated comparison
circuitry. CAMs are hardware-based search engines that are much faster than algorithmic
approaches for search-intensive applications. CAMs are especially popular in network devices,
which require high-speed table lookup for packet switching and forwarding.
- The default ARP table aging time is 4 hours (14400 seconds); while the default MAC address
table aging time is 5 minutes (300 seconds). Aging time is the period that an entry is being kept.
- The arp timeout {seconds} interface subcommand and mac-address-table aging-time
{seconds} global configuration command modify the ARP table aging timer and MAC address
table aging timer respectively.
- A balanced line is a transmission line that consists of 2 connectors of the same type which there
is no master-slave relationship – the DTE and DCE are treated as equals. Each station may
initialize, supervise, recovery from errors, and send frames at any time.
- A balun can be used to convert balanced signal to unbalanced signal.
- Alignment error is an error that occurs in Ethernet networks, where a received frame has extra
bits – a number that is not divisible by 8. Alignment errors are generally caused by collisions and
eventually frame damage.
- Bit-oriented protocols are data link layer protocols that transmit frames regardless of the frame
content. Byte-oriented protocols use a specific character from the user character set to mark the
boundaries of frames. As compared with byte-oriented protocols, bit-oriented protocols are more
efficient and support full-duplex operation. As a result, byte-oriented protocols have been
superceded or replaced by bit-oriented protocols.
- Broadcasts and IP networks are not limited to VLANs, even though it is very tempting to think so.
If 2 switches are connected with a crossover cable, with one configured with VLAN 10 on all
ports, and another configured with VLAN 20 on all ports; hosts that connected to the switches
are able to communicate as they as on the same IP network!
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Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com