Network Protocols and Port Numbers

Port Numbers

• Well-known port numbers are those below 1024.
• Dynamically assigned port numbers are above 1024.
• Registered port numbers are mainly above 1024, designated for vendor-specific applications.

Domain Name Service (DNS)

• Translates domain names into IP addresses.
• There are over 200 top-level domains on the internet.

FTP and TFTP

• FTP (File Transfer Protocol) is a connection-oriented service using TCP, ensuring reliable file transfers.
• TFTP (Trivial File Transfer Protocol) is connectionless and uses UDP, commonly used on routers for transferring configuration files.
• TFTP is designed to be small and easy to implement.

SNMP

• Simple Network Management Protocol, facilitates management information exchange between network devices.

TELNET

• Client software for logging into remote internet hosts running telnet server applications.
• Allows execution of commands from the command line interface.

Access Control Lists (ACLs)

• A Layer 3 security measure controlling traffic between routers, referred to as Packet Filtering Firewalls.
• Types of ACLs:
  • Standard ACL
  • Extended ACL
  • Named ACL

Standard Access List

• Number range is 1-99.
• Capable of blocking network, host, and subnet traffic.
• Stops two-way communication and blocks all services.
• Implemented closest to the destination.

Configuration Commands for Access Lists

• Create a standard named access list:
  • Router(config)# ip access-list standard
• Implement a standard named access list:
  • Router(config)#interface
  • Router(config-if)#ip access-group

Extended Access List

• Create an extended named access list:
  • Router(config)# ip access-list extended <destination wildcard mask>
• Implementation follows similar commands as standard lists.

Bridge Basics

• Bridge ID combines bridge priority and MAC address to track all switches in the network.
• Non-root bridges exchange BPDUs with all other bridges to maintain STP topology.

Port Costs and Convergence

• Link cost determined by bandwidth.
• Path cost is the cumulative cost to the root bridge.
• BPDUs contain information about ports, costs, and priorities.
• Convergence occurs when ports transition to forwarding or blocking states. Original STP (802.1d) takes 50 seconds to transition from blocking to forwarding.

Bridge Port Roles

• Root Port: Best path to the root bridge; all non-root bridges must have this.
• Designated Port: Lowest cost to access a specific network segment.
• Non-designated Port: Highest cost, kept in a blocked state.
• Forwarding Port: Capable of forwarding frames.
• Blocked Port: Receives only BPDUs.
• Alternate and Backup Ports: Related to blocking states in STP and RSTP, respectively.

Spanning-Tree Port States

• Disabled: Non-operational state.
• Blocking: Does not forward frames; only listens to BPDUs.

Dynamic ARP Inspection (DAI)

• Works with DHCP snooping to protect against ARP poisoning by rejecting invalid ARP packets.
• Maintains a binding database of valid (MAC address, IP address) pairs.

Identity-based Networking

• Integrates several components to provide users with network services.
• IEEE 802.1x standard can be employed for identity-based networking in wired and wireless hosts.

External Authentication Options

• RADIUS: Combines authentication and authorization; follows a three-stage authentication process.
• TACACS+: Cisco's proprietary security server using TCP for authentication.

Voice and Video Traffic

• Voice Traffic:

  • Sensitive to delays/drops; uses UDP and has no retransmission for lost packets.
  • Flows evenly and requires low bandwidth per call.

• Video Traffic:

  • Also sensitive to delays/drops with no retransmission.
  • Characteristics include burstiness and higher bandwidth demands for better quality.

Traffic Management Algorithms

• FIFO (First In First Out): Processes traffic in the order received without prioritization.
• WFQ (Weighted Fair Queuing): Prioritizes interactive traffic for quicker response times and shares bandwidth among high-volume flows fairly.

Quality of Service (QoS) Technologies

• Enhance network services for edge applications using mechanisms such as Best Effort and Integrated Services.