networking-essentials

# Networking Essentials ## Purpose Provide foundational networking knowledge required for penetration testing including OSI model concepts, TCP/IP addressing, subnetting, cable standards, and Cisco device configuration. Enable understanding of network infrastructure for effective security assessments. ## Inputs/Prerequisites - Basic computer literacy - Access to network devices or simulator (Packet Tracer, GNS3) - Understanding of binary and hexadecimal notation - Network topology information for target environment ## Outputs/Deliverables - Properly configured network infrastructure - Subnetting calculations and IP schemes - VLAN segmentation plans - Router and switch configurations - Network documentation for assessments ## Core Workflow ### 1. Understand Network Types **Network Categories:** - **LAN (Local Area Network)**: Single location, high speed - **WAN (Wide Area Network)**: Multiple locations, geographic dispersion - **Internet**: Global interconnection of networks **LAN Architectures:** - **Client/Server**: Centralized resources and management - **Peer-to-Peer**: Decentralized, each device shares resources ### 2. Master Cable Standards **UTP Cable Categories:** | Category | Speed | Use Case | |----------|-------|----------| | CAT 3 | 10 Mbps | Ethernet | | CAT 5 | 100 Mbps | Fast Ethernet | | CAT 5e | 1 Gbps | Gigabit Ethernet | | CAT 6 | 1 Gbps | Multi-Gigabit | **Cable Wiring Standards:** **Straight-Through (T568A to T568A):** - Use: PC to Switch, Router to Switch - Pin 1-8 same on both ends **Crossover (T568A to T568B):** - Use: PC to PC, Switch to Switch, Router to Router - Transmit/Receive pairs swapped **T568A Pinout:** 1. Green/White (TX+) 2. Green (TX-) 3. Orange/White (RX+) 4. Blue 5. Blue/White 6. Orange (RX-) 7. Brown/White 8. Brown ### 3. Apply OSI Model **Seven Layers (Top to Bottom):** | Layer | Name | Function | Protocols/Devices | |-------|------|----------|-------------------| | 7 | Application | User interface | HTTP, FTP, SMTP | | 6 | Presentation | Data formatting | SSL, JPEG, ASCII | | 5 | Session | Connection management | NetBIOS, RPC | | 4 | Transport | End-to-end delivery | TCP, UDP | | 3 | Network | Routing and addressing | IP, ICMP, Routers | | 2 | Data Link | Frame transmission | Ethernet, Switches | | 1 | Physical | Bit transmission | Cables, Hubs | **Remember:** "All People Seem To Need Data Processing" ### 4. Configure TCP/IP Addressing **IP Address Classes:** | Class | Range | Default Mask | Networks | |-------|-------|--------------|----------| | A | 1-126 | 255.0.0.0 | Large organizations | | B | 128-191 | 255.255.0.0 | Medium organizations | | C | 192-223 | 255.255.255.0 | Small organizations | **Private IP Ranges:** - Class A: 10.0.0.0 - 10.255.255.255 - Class B: 172.16.0.0 - 172.31.255.255 - Class C: 192.168.0.0 - 192.168.255.255 **Subnetting Calculation:** ``` Network: 192.168.1.0/26 Subnet Mask: 255.255.255.192 Subnets: 2^2 = 4 subnets Hosts per subnet: 2^6 - 2 = 62 hosts Subnet 1: 192.168.1.0 - 192.168.1.63 Subnet 2: 192.168.1.64 - 192.168.1.127 Subnet 3: 192.168.1.128 - 192.168.1.191 Subnet 4: 192.168.1.192 - 192.168.1.255 ``` ### 5. Configure Cisco Routers **Basic Router Commands:** ``` ! Enter privileged mode Router> enable Router# ! Enter configuration mode Router# configure terminal Router(config)# ! Set hostname Router(config)# hostname R1 ! Configure interface Router(config)# interface FastEthernet 0/0 Router(config-if)# ip address 192.168.1.1 255.255.255.0 Router(config-if)# no shutdown ! Save configuration Router# copy running-config startup-config ! Show commands Router# show ip interface brief Router# show running-config Router# show ip route ``` **Configure Static Routing:** ``` Router(config)# ip route 10.0.0.0 255.0.0.0 192.168.1.2 Router(config)# ip route 0.0.0.0 0.0.0.0 192.168.1.1 ! Default route ``` **Configure RIP Routing:** ``` Router(config)# router rip Router(config-router)# version 2 Router(config-router)# network 192.168.1.0 Router(config-router)# network 10.0.0.0 ``` ### 6. Configure Cisco Switches **Basic Switch Commands:** ``` ! Configure management VLAN Switch(config)# interface vlan 1 Switch(config-if)# ip address 192.168.1.10 255.255.255.0 Switch(config-if)# no shutdown ! Configure port Switch(config)# interface FastEthernet 0/1 Switch(config-if)# switchport mode access Switch(config-if)# switchport access vlan 10 ``` **VLAN Configuration:** ``` ! Create VLAN Switch(config)# vlan 10 Switch(config-vlan)# name SALES Switch(config-vlan)# exit ! Assign port to VLAN Switch(config)# interface range fa0/1-10 Switch(config-if-range)# switchport access vlan 10 ! Configure trunk port Switch(config)# interface GigabitEthernet 0/1 Switch(config-if)# switchport mode trunk Switch(config-if)# switchport trunk allowed vlan 10,20,30 ``` **Inter-VLAN Routing (Router-on-a-Stick):** ``` Router(config)# interface FastEthernet 0/0.10 Router(config-subif)# encapsulation dot1Q 10 Router(config-subif)# ip address 192.168.10.1 255.255.255.0 Router(config)# interface FastEthernet 0/0.20 Router(config-subif)# encapsulation dot1Q 20 Router(config-subif)# ip address 192.168.20.1 255.255.255.0 ``` ### 7. Configure Access Lists **Standard ACL (Filter by Source IP):** ``` ! Deny specific host Router(config)# access-list 10 deny host 192.168.1.100 Router(config)# access-list 10 permit any ! Apply to interface Router(config)# interface FastEthernet 0/0 Router(config-if)# ip access-group 10 in ``` **Extended ACL (Filter by Source, Destination, Port):** ``` ! Block Telnet from specific network Router(config)# access-list 100 deny tcp 192.168.1.0 0.0.0.255 any eq 23 Router(config)# access-list 100 permit ip any any ! Apply to interface Router(config-if)# ip access-group 100 in ``` ### 8. Configure NAT **Static NAT:** ``` Router(config)# ip nat inside source static 192.168.1.10 203.0.113.10 Router(config)# interface FastEthernet 0/0 Router(config-if)# ip nat inside Router(config)# interface Serial 0/0 Router(config-if)# ip nat outside ``` **Dynamic NAT with PAT:** ``` Router(config)# access-list 1 permit 192.168.1.0 0.0.0.255 Router(config)# ip nat pool MYPOOL 203.0.113.1 203.0.113.1 netmask 255.255.255.0 Router(config)# ip nat inside source list 1 pool MYPOOL overload ``` ## Quick Reference ### Common Subnet Masks | CIDR | Mask | Hosts | |------|------|-------| | /24 | 255.255.255.0 | 254 | | /25 | 255.255.255.128 | 126 | | /26 | 255.255.255.192 | 62 | | /27 | 255.255.255.224 | 30 | | /28 | 255.255.255.240 | 14 | | /29 | 255.255.255.248 | 6 | | /30 | 255.255.255.252 | 2 | ### Essential Show Commands ``` show ip interface brief show running-config show ip route show vlan brief show interfaces trunk show access-lists show ip nat translations ``` ## Constraints - VLAN hopping attacks possible without proper trunk security - Weak ACLs can be bypassed - NAT can complicate penetration testing - Routing protocols can be exploited if not secured - Switch CAM tables can be flooded ## Examples ### Example 1: Basic Network Scan Understanding ```bash # Scan reveals network structure nmap -sn 192.168.1.0/24 # Identify VLANs through ARP arp-scan -l # Discover routing traceroute 10.0.0.1 ``` ### Example 2: VLAN Enumeration ```bash # Check for VLAN hopping vulnerability yersinia -G # DTP attack (if trunk misconfigured) yersinia dtp -attack 1 ``` ## Troubleshooting | Issue | Solution | |-------|----------| | No connectivity | Verify cable type (straight vs crossover) | | Cannot reach gateway | Check IP configuration and subnet mask | | VLAN isolation | Verify trunk configuration and allowed VLANs | | Routing not working | Check ip routing enabled and routes configured | | ACL blocking traffic | Review access-list and interface application | | NAT not translating | Verify inside/outside interface designation |