Huawei HCIA-Datacom cheat sheet

OSI layers from bottom to top are physical, data link, network, transport, session, presentation, and application; TCP/IP maps them to network access, internet, transport, and application layers.

Encapsulation adds headers at each layer: data becomes a segment at transport, a packet at network, a frame at data link, and bits at physical.

TCP is connection-oriented and uses a three-way handshake (SYN, SYN-ACK, ACK), sequence numbers, acknowledgments, and retransmission; UDP is connectionless with no handshake or delivery guarantee.

Common TCP/UDP ports: FTP 20/21, SSH 22, Telnet 23, SMTP 25, DNS 53, DHCP 67/68, HTTP 80, HTTPS 443, SNMP 161/162, NTP 123.

ARP resolves an IPv4 address to a MAC address on the local link; the reply is cached in the ARP table and gratuitous ARP can detect duplicate addresses.

IPv4 traffic types are unicast (one-to-one), broadcast (one-to-all on a subnet), and multicast (one-to-group); IPv6 has unicast, multicast, and anycast but no broadcast.

Bandwidth is the maximum link capacity, while throughput is actual delivered rate; delay components include propagation, transmission, processing, and queuing delay.

IPv4 classful ranges: A 1-126, B 128-191, C 192-223, D 224-239 multicast, E 240-255 experimental; 127.0.0.0/8 is loopback.

Private IPv4 ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16; 169.254.0.0/16 is link-local and 0.0.0.0/0 is the default route.

CIDR notation gives prefix length; subnet mask bits set to 1 identify the network portion, and VLSM allows different mask lengths inside one major network.

A router forwards using the longest-prefix match among routes that match the destination; the default route matches only when no more specific route exists.

Huawei default route preferences: direct 0, OSPF internal 10, static 60, RIP 100, OSPF external 150, BGP 255; lower values are preferred.

Static route command form: ip route-static destination mask next-hop or ip route-static destination mask interface; a floating static route uses a higher preference.

OSPF uses area 0 as the backbone; on broadcast networks default hello is 10 s and dead is 40 s, and routers elect a DR and BDR to reduce adjacencies.

OSPF router ID selection order is highest configured router ID, highest loopback address, then highest physical interface address.

A switch learns source MAC addresses and their ingress ports into the MAC table and forwards known unicast frames only out the matching port; unknown unicast is flooded.

VLAN IDs are 1-4094; VLAN 1 is the default VLAN, and VLANs divide one physical switch into separate broadcast domains.

Access ports belong to one VLAN and usually connect hosts; trunk ports carry multiple VLANs and insert 802.1Q tags, except optionally on the native VLAN.

An 802.1Q tag is 4 bytes and contains a 12-bit VLAN identifier, giving up to 4094 usable VLANs; untagged frames on a trunk belong to the native VLAN.

STP elects one root bridge by lowest bridge ID (priority plus MAC); default bridge priority is 32768, and lower priority is better.

STP port states are blocking, listening, learning, forwarding, and disabled; RSTP uses discarding, learning, and forwarding with root, designated, alternate, and backup roles.

RSTP edge ports connect to end devices, enter forwarding immediately, and should be configured with BPDU protection to prevent loops.

Link aggregation combines links into an Eth-Trunk; LACP active mode initiates LACPDUs, passive mode responds, and at least one side must be active.

Huawei ACL number ranges: basic 2000-2999, advanced 3000-3999, Layer 2 4000-4999, and user-defined 6000-6999.

Advanced ACLs can match source and destination IP addresses, protocol, source and destination ports, and TCP flags; rules are checked in sequence and the first match applies.

NAT types include static NAT (one-to-one), dynamic NAT (pool-based), NAPT/PAT (many-to-one with port translation), and Easy IP (uses the interface public address).

NAT Server maps a public IP address and port to an internal server, allowing external clients to initiate sessions to an internal service.

DHCP uses the DORA exchange: Discover, Offer, Request, Acknowledge; server UDP port is 67, client UDP port is 68, and leases include address, mask, gateway, and DNS options.

AAA provides authentication (identity), authorization (permissions), and accounting (usage records); RADIUS uses UDP 1812 for authentication/authorization and UDP 1813 for accounting.

HWTACACS uses TCP port 49 and separates authentication, authorization, and accounting more fully than RADIUS, commonly for device administration.

A DHCP relay agent forwards client broadcasts as unicast to a DHCP server on another subnet using the giaddr field.

PPP operates at the data link layer and uses LCP for link establishment, authentication, and negotiation, plus NCPs such as IPCP for network-layer parameters.

PPP authentication options are PAP, which sends a clear-text password, and CHAP, which uses a challenge-response hash and does not send the password across the link.

PPP has link establishment, authentication, network-layer negotiation, and termination phases; multilink PPP can bundle multiple links.

HDLC is a bit-oriented data link protocol using flag 0x7E, address and control fields, FCS, and zero-bit insertion to avoid flag patterns in data.

PPPoE has a discovery stage that assigns a session ID and a session stage that carries PPP frames over Ethernet, commonly used for broadband access.

WAN access options include leased lines, PPPoE/DSL, cable, Ethernet metropolitan access, and cellular 4G/5G access.

Huawei serial interfaces default to PPP link-layer encapsulation; HDLC is also supported but is not the Huawei default.

SNMP managers query agents on UDP 161 and receive traps or notifications on UDP 162; managed objects are defined in a MIB and identified by OIDs.

SNMPv1 and SNMPv2c use community strings in clear text; SNMPv3 adds authentication and encryption through user-based security model parameters.

NTP uses UDP port 123 and a hierarchical stratum model: stratum 0 is a reference clock, stratum 1 servers attach directly, and higher strata increase in number away from the source.

Telnet uses TCP 23 and sends data in clear text; SSH uses TCP 22 and encrypts the session; VTY lines control remote login and should be restricted by ACL and AAA.

FTP uses TCP 20 for active-mode data and TCP 21 for control; TFTP uses UDP 69 and provides no authentication or encryption.

Syslog uses UDP 514 and eight severity levels from 0 emergency to 7 debugging; lower numbers indicate more severe events.

Huawei configuration workflow includes system-view, interface configuration, commit or save, and verification with display commands; configuration files are saved with save.

An IPv6 address is 128 bits, written as eight 16-bit hexadecimal groups; leading zeros in a group may be omitted and one contiguous run of zero groups may be replaced by ::.

IPv6 address types include unicast, multicast, and anycast; there is no broadcast, and multicast replaces broadcast functions.

Global unicast addresses use 2000::/3, link-local uses FE80::/10, unique local uses FC00::/7, loopback is ::1, and unspecified is ::.

Every IPv6 interface automatically has a link-local address; it is used for neighbor discovery and next-hop resolution and is not forwarded by routers.

Neighbor Discovery uses RS/RA for router and prefix discovery and NS/NA for address resolution and duplicate address detection, replacing ARP.

SLAAC lets hosts build addresses from an RA-advertised prefix plus an interface identifier, often derived by EUI-64 or privacy extensions.

The IPv6 header is a fixed 40 bytes with a Next Header field for extension headers; the Hop Limit field replaces the IPv4 TTL.

In Router Advertisement flags, M=1 directs hosts to stateful DHCPv6 for addresses, and O=1 directs hosts to DHCPv6 for other configuration.

SDN separates the application, control, and data planes; a centralized controller computes and installs forwarding policy on devices through southbound interfaces.

Southbound SDN interfaces include OpenFlow and NETCONF; northbound interfaces are typically RESTful APIs used by applications and orchestration systems.

VXLAN encapsulates Layer 2 frames in UDP, uses destination port 4789 by default, has an 8-byte header, and carries a 24-bit VNI supporting about 16 million segments.

VXLAN tunnel endpoints (VTEPs) encapsulate and decapsulate traffic; the underlay must route the VTEP loopback addresses, while the overlay carries tenant Layer 2 domains.

NETCONF uses XML-encoded RPCs, usually over SSH on TCP 830, with operations such as get, get-config, edit-config, and candidate configuration support.

YANG is a data modeling language for NETCONF and RESTCONF; RESTCONF typically runs over HTTPS and uses HTTP methods GET, POST, PUT, PATCH, and DELETE.

RESTful APIs are stateless, use HTTP status codes, and commonly exchange JSON or XML; Python requests can call these APIs with get, post, put, and delete methods.

Python automation libraries include ncclient for NETCONF, requests for REST APIs, and Paramiko or Netmiko for SSH-based CLI interaction.