| CIDR | Subnet Mask | Host Bits | Hosts |
|---|---|---|---|
| /32 | 255.255.255.255 | 0 | 1 (Host) |
| /31 | 255.255.255.254 | 1 | 0 (P2P) |
| /30 | 255.255.255.252 | 2 | 2 |
| /29 | 255.255.255.248 | 3 | 6 |
| /28 | 255.255.255.240 | 4 | 14 |
| /27 | 255.255.255.224 | 5 | 30 |
| /26 | 255.255.255.192 | 6 | 62 |
| /25 | 255.255.255.128 | 7 | 126 |
| /24 | 255.255.255.0 | 8 | 254 |
| /23 | 255.255.254.0 | 9 | 510 |
| /22 | 255.255.252.0 | 10 | 1,022 |
| /21 | 255.255.248.0 | 11 | 2,046 |
| /20 | 255.255.240.0 | 12 | 4,094 |
| /19 | 255.255.224.0 | 13 | 8,190 |
| /18 | 255.255.192.0 | 14 | 16,382 |
| /17 | 255.255.128.0 | 15 | 32,766 |
| /16 | 255.255.0.0 | 16 | 65,534 |
| /15 | 255.254.0.0 | 17 | 131,070 |
| /14 | 255.252.0.0 | 18 | 262,142 |
| /13 | 255.248.0.0 | 19 | 524,286 |
| /12 | 255.240.0.0 | 20 | 1,048,574 |
| /11 | 255.224.0.0 | 21 | 2,097,150 |
| /10 | 255.192.0.0 | 22 | 4,194,302 |
| /9 | 255.128.0.0 | 23 | 8,388,606 |
| /8 | 255.0.0.0 | 24 | 16,777,214 |
| Identifier | Protocol | Header Type | CCNA 200-301 Exam Context |
|---|---|---|---|
| Protocol 1 | ICMP | IP Protocol (L3) | Internet Control Message Protocol (Ping / Traceroute) |
| Protocol 6 | TCP | IP Protocol (L3) | Transmission Control Protocol (Reliable, Connection-Oriented) |
| Protocol 17 | UDP | IP Protocol (L3) | User Datagram Protocol (Unreliable, Connectionless) |
| Protocol 47 | GRE | IP Protocol (L3) | Generic Routing Encapsulation (Site-to-Site VPN Tunnels) |
| Protocol 50 | IPsec ESP | IP Protocol (L3) | Encapsulating Security Payload (IPsec Data Encryption & Auth) |
| Protocol 51 | IPsec AH | IP Protocol (L3) | Authentication Header (IPsec Data Integrity & Auth) |
| Protocol 58 | ICMPv6 | IPv6 Next Header | IPv6 Neighbor Discovery (NDP), Router Solicit/Advert (RS/RA) |
| Protocol 88 | EIGRP | IP Protocol (L3) | Enhanced Interior Gateway Routing Protocol (Cisco) |
| Protocol 89 | OSPF | IP Protocol (L3) | Open Shortest Path First (OSPFv2 & OSPFv3) |
| Port 20, 21 | FTP | TCP Port (L4) | File Transfer Protocol (Data: 20, Control: 21) |
| Port 22 | SSH | TCP Port (L4) | Secure Shell (Encrypted Remote CLI Access) |
| Port 23 | Telnet | TCP Port (L4) | Unencrypted Remote CLI Access (Plaintext) |
| Port 25 | SMTP | TCP Port (L4) | Simple Mail Transfer Protocol (Email Sending) |
| Port 49 | TACACS+ | TCP Port (L4) | Cisco AAA Architecture (Encrypts Entire Packet Payload) |
| Port 53 | DNS | TCP / UDP Port (L4) | Domain Name System (UDP Queries, TCP Zone Transfers) |
| Port 67, 68 | DHCP | UDP Port (L4) | Dynamic Host Config Protocol (Server: 67, Client: 68) |
| Port 69 | TFTP | UDP Port (L4) | Trivial File Transfer Protocol (Unreliable, No Auth) |
| Port 80 | HTTP | TCP Port (L4) | Hypertext Transfer Protocol (Unencrypted Web) |
| Port 123 | NTP | UDP Port (L4) | Network Time Protocol (Clock Sync across Network) |
| Port 161, 162 | SNMP | UDP Port (L4) | Simple Network Mgmt (Agent Poll: 161, Traps: 162) |
| Port 179 | BGP | TCP Port (L4) | Border Gateway Protocol (Path-Vector Exterior Routing) |
| Port 443 | HTTPS | TCP Port (L4) | HTTP Secure (Encrypted Web Traffic via TLS/SSL) |
| Port 514 | Syslog | UDP Port (L4) | System Logging (Default Remote Log Server Port) |
| Port 1812, 1813 | RADIUS | UDP Port (L4) | Open AAA Standard (Auth/Authz: 1812, Accounting: 1813) |
| Route Source / Protocol | AD Value | Default Status & Context |
|---|---|---|
| Connected Interface | 0 | Highest possible trustworthiness |
| Static Route | 1 | Default static route preference |
| EIGRP Summary Route | 5 | Auto or manual summary route to Null0 |
| External BGP (eBGP) | 20 | Routes learned from external Autonomous System |
| Internal EIGRP | 90 | Normal EIGRP routes within same AS |
| OSPF | 110 | Open Shortest Path First (Inter-area, Intra-area, External) |
| IS-IS | 115 | Intermediate System to Intermediate System |
| RIP | 120 | Routing Information Protocol (v1 / v2) |
| External EIGRP | 170 | Redistributed routes into EIGRP |
| Internal BGP (iBGP) | 200 | Routes learned via BGP within same AS |
| DHCP Default Route | 254 | Default route assigned via DHCP client |
| Unusable / Untrusted | 255 | Route will not be installed in Routing Table (RIB) |
| Prefix / Address | Address Type | Description & Scope |
|---|---|---|
| ::/128 | Unspecified | Used as source address before host receives IP assignment |
| ::1/128 | Loopback | Local host loopback testing (equivalent to 127.0.0.1) |
| 2000::/3 | Global Unicast (GUA) | Globally routable public IPv6 range (2000:: to 3FFF::) |
| fe80::/10 | Link-Local | Auto-configured on every IPv6 interface (Non-routable) |
| fc00::/7 (fd00::/8) | Unique Local (ULA) | Private IPv6 addressing (equivalent to RFC 1918 IPv4) |
| ff00::/8 | Multicast Range | All IPv6 multicast destination addresses |
| ff02::1 | Multicast | All IPv6 Nodes on local link (Replaces IPv4 Broadcast) |
| ff02::2 | Multicast | All IPv6 Routers on local link |
| ff02::5 | Multicast | All OSPFv3 Routers |
| ff02::6 | Multicast | OSPFv3 Designated Routers (DR / BDR) |
| ff02::9 | Multicast | All RIPng Routers |
| ff02::a | Multicast | All EIGRPv6 Routers |
| ff02::1:ff00:0/104 | Solicited-Node | Used for ARP replacement (NDP Neighbor Solicitation) |
| Component / Header | Category | Contents & Details |
|---|---|---|
| RAM | Volatile Memory | Running-config, ARP cache, Routing table (RIB), MAC table, Buffers |
| NVRAM | Non-Volatile Memory | Startup-config file, Configuration register setting |
| Flash Memory | Non-Volatile Memory | Cisco IOS operating system image (.bin file), vlan.dat file |
| ROM | Non-Volatile Memory | POST (Power-On Self Test), Bootstrap program, ROMmon recovery mode |
| 0x2102 | Config Register | Normal default boot process (Loads IOS from Flash, startup-config from NVRAM) |
| 0x2142 | Config Register | Bypasses NVRAM startup-config on boot (Used for Password Recovery!) |
| EtherType 0x0800 | Ethernet Frame | IPv4 Data Packet Payload |
| EtherType 0x0806 | Ethernet Frame | ARP (Address Resolution Protocol) Frame Payload |
| EtherType 0x86DD | Ethernet Frame | IPv6 Data Packet Payload |
| EtherType 0x8100 | Ethernet Frame | 802.1Q VLAN Tagged Frame Header |
| MAC 01-00-5E-xx-xx-xx | Multicast MAC | IPv4 Multicast Destination MAC (01-00-5E + 23 bits of IPv4 Multicast IP) |
| MAC 33-33-xx-xx-xx-xx | Multicast MAC | IPv6 Multicast Destination MAC (33-33 + last 32 bits of IPv6 Multicast IP) |
| Standard / Concept | Type / Frequency | Key Details & CCNA Specifications |
|---|---|---|
| 802.1D (Classic STP) | Legacy STP | Port states: Blocking -> Listening (15s) -> Learning (15s) -> Forwarding. Hello: 2s, Max Age: 20s |
| 802.1w (RSTP) | Rapid STP | Port states: Discarding -> Learning -> Forwarding. Fast convergence via proposal/agreement handshake |
| 802.1s (MSTP) | Multiple STP | Maps multiple VLANs to STP instances to save CPU resources |
| 802.11b | Wi-Fi 1 (2.4 GHz) | Max Speed: 11 Mbps (DSSS modulation, non-overlapping channels 1, 6, 11) |
| 802.11a | Wi-Fi 2 (5 GHz) | Max Speed: 54 Mbps (OFDM modulation) |
| 802.11g | Wi-Fi 3 (2.4 GHz) | Max Speed: 54 Mbps (Backward compatible with 802.11b) |
| 802.11n | Wi-Fi 4 (2.4 & 5 GHz) | Max Speed: 600 Mbps (Introduced MIMO & Channel Bonding 40MHz) |
| 802.11ac | Wi-Fi 5 (5 GHz) | Max Speed: 6.9 Gbps (MU-MIMO, 80/160MHz Channels, 256-QAM) |
| 802.11ax | Wi-Fi 6 / 6E (2.4/5/6GHz) | Max Speed: 9.6 Gbps (OFDMA, 1024-QAM, Target Wake Time) |