Questions and Answers
What is the primary function of the Bridge ID?
What is the main purpose of BPDUs?
What is the state of all ports on bridges and switches after convergence?
What is the root port of a non-root bridge?
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What is the purpose of the designated port?
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What is the main difference between the original STP (802.1d) and RSTP (802.1w)?
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What is the term used in RSTP to describe the blocking state?
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What is the path cost in a spanning tree network?
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What is the function of a non-designated port?
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What is the purpose of a backup port?
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Study Notes
Reliability and Flow Control
- Reliability in transport ensures segments are delivered and acknowledged, with retransmission of unacknowledged segments and correct sequencing at the destination.
- It also provides congestion avoidance and control.
- Flow control avoids buffer overflow at the receiving host by managing data transmission.
Acknowledgment
- Positive acknowledgment requires the recipient to send an acknowledgment message to the sender upon receiving data.
- The sender keeps a record of each data packet sent and expects an acknowledgment.
TCP and UDP
- TCP is a reliable, connection-oriented protocol used by:
- FTP (File Transfer Protocol)
- HTTP (Hypertext Transfer Protocol)
- SMTP (Simple Mail Transfer Protocol)
- Telnet
- UDP is a connectionless protocol used by:
- TFTP (Trivial File Transfer Protocol)
- SNMP (Simple Network Management Protocol)
- DHCP (Dynamic Host Control Protocol)
- DNS (Domain Name System)
TCP and UDP Ports
- Both TCP and UDP use port numbers to pass information to upper layers.
- Well-known port numbers are below 1024, while dynamically assigned port numbers are above 1024.
- Registered port numbers are used for vendor-specific applications, mainly above 1024.
File Transfer Protocols
- FTP is a reliable, connection-oriented service that uses TCP to transfer files between FTP-supporting systems.
- TFTP is a connectionless service that uses UDP, used for transferring configuration files and Cisco IOS images on routers.
SNMP
- SNMP is an application layer protocol that facilitates the exchange of management information between network devices.
Access Control Lists (ACLs)
Types of Access Lists
- Standard ACL: access-list number 1-99, can block a network, host, or subnet, stops two-way communication, and is implemented closest to the destination.
- Extended ACL: access-list number 100-199, can block a network, host, subnet, and service, stops one-way communication, and is implemented closest to the source.
- Named ACL: uses names instead of numbers, allows editing, and has no number limitations.
Wild Card Mask
- Tells the router which addressing bits must match in the ACL statement.
- It's the inverse of the subnet mask, also called the inverse mask.
- A bit value of 0 indicates MUST MATCH, while a bit value of 1 indicates IGNORE.
Creation and Implementation of Access Lists
- Standard Named ACL:
ip access-list standard
andinterface
commands. - Extended Named ACL:
ip access-list extended
andinterface
commands. - Standard ACL:
access-list
command. - Extended ACL:
access-list
command with destination wildcard mask.
Verification of Access-List Configuration
-
show access-list
command displays all access lists and their parameters configured on the router.
Spanning Tree Protocol (STP)
- Bridge ID: determined by bridge priority and MAC address, used to keep track of all switches in the network.
- Non-root bridges: exchange BPDUs with all bridges and update STP topology database.
- Port Cost: determined by link bandwidth.
- Path Cost: sum of port costs to the root bridge.
- BPDU: data messages exchanged between switches containing information about ports, costs, priorities, and bridge ID.
- Convergence: all ports on bridges and switches have transitioned to either forwarding or blocking modes.
Bridge Port Roles
- Root Port: the port with the best path to the root bridge, placed in forwarding state.
- Designated Port: has the best cost to get to a network segment, placed in forwarding state.
- Non-designated Port: has the highest cost and is kept blocked.
- Forwarding Port: forwards frames, can be either a root port or a designated port.
- Blocked Port: only receives BPDU frames from other switches.
- Alternate Port: corresponds to the blocking state of 802.1d, used with RSTP (802.1w).
- Backup Port: connected on a LAN segment with another port on the same switch acting as the designated port.
Spanning-Tree Port States
- Disabled: non-operational state.
- Blocking: port does not forward frames, only listens to BPDUs.
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Description
This quiz covers the basics of reliability and flow control in computer networks, including ensuring segment delivery and retransmission, sequencing, and congestion avoidance.