Data Communication + Network Basics
8%of exam
IP Network Interconnection + Interworking
27%of exam
SubnettingRoute ChoiceStatic RoutingOSPF
Ethernet Switching Network Construction
28%of exam
Cyber Security Infrastructure + Network Access
8%of exam
ACL TypesAAANAT TypesTraffic Filter
Network Services + Applications
5%of exam
WLAN Basics
10%of exam
WLAN RolesCAPWAPWLAN JoinForwarding Modes
WAN Basics
3%of exam
Network Management + O&M
3%of exam
SNMP RolesSNMP MessagesO&M ChecksDisplay Commands
IPv6 Basics
5%of exam
IPv6 AddressingAddress TypesNeighbor DiscoveryIPv6 Routing
SDN + Automation Basics
3%of exam
SDN PlanesSDN APIsNFVPython Basics
Quick Facts
- Exam
- H12-811
- Version
- HCIA-Datacom V1.0
- Languages
- ENU / CHS
- Duration
- 90 minutes
- Pass score
- 600 / 1000
- Exam cost
- US$200
- Domains
- 10
- Largest domain
- Ethernet switching 28%
TCP vs UDP
TCP
- Connection-oriented
- Reliable delivery
- Flow control
UDP
- Connectionless
- Best effort
- Lower overhead
Reliability vs speed
Models + Forwarding
- OSI Layer 1
- Bits + physical media
- OSI Layer 2
- Frames + MAC
- OSI Layer 3
- Packets + IP routing
- OSI Layer 4
- Segments + ports
- Encapsulation
- Adds layer headers
- ARP
- IPv4 address to MAC
- TCP
- Reliable connection-oriented transport
- UDP
- Fast connectionless transport
VRP Quick Commands
- <Huawei>
- User view
- [Huawei]
- System view
- system-view
- Enter configuration
- quit
- One view upward
- return
- Jump to user view
- undo
- Negate configuration
- save
- Persist current configuration
- display current-configuration
- Show running configuration
OSPF Neighbor States
Down Init 2-Way ExStart Exchange Loading Full
2-Way: DR decisionExStart: negotiate masterExchange: share DBDsFull: synchronized
Preference vs Cost
Preference
- Compares route sources
- Lower wins
Cost
- Compares OSPF paths
- Lower wins
Protocol trust vs path
Route Choice Picker
- Destination same subnet→ARP destination(Direct delivery)
- Destination remote subnet→ARP gateway(Router forwards)
- Need fixed path→Static route
- Need dynamic routes→OSPF
- Need fallback exit→Default route
- Different prefix lengths→Longest match
- Different route sources→Route preference
- Same OSPF destination→Lowest cost
IPv4 + Route Choice
- IPv4
- 32-bit addressing
- Typical usable hosts
- 2^h minus 2
- Network address
- Host bits all zero
- Broadcast address
- Host bits all one
- Default route
- 0.0.0.0/0
- Longest match
- Most specific prefix wins
- Route preference
- Lower value wins
- Direct / OSPF / Static
- Preference 0 / 10 / 60
Static Routing + OSPF
- ip route-static
- Add IPv4 static route
- Floating static
- Larger preference becomes backup
- OSPF
- Link-state interior protocol
- Area 0
- OSPF backbone
- Router ID
- 32-bit OSPF identifier
- OSPF cost
- Lower path cost wins
- DR election
- Highest priority then RID
- network command
- Enable matching interfaces
STP Root Election
Root: lowest priority, then lowest MAC
Lowest BID winsRoot has no root portPath cost picks root port
Access vs Trunk
Access
- One VLAN
- Endpoint-facing
- Untagged frames
Trunk
- Multiple VLANs
- Device interconnect
- Tagged VLANs
One VLAN vs many
Switching Picker
- Single endpoint VLAN→Access port
- Multiple tagged VLANs→Trunk port
- Mixed tag behavior→Hybrid port
- Route between VLANs→VLANIF
- Redundant Layer 2 links→STP
- Need faster convergence→RSTP
- Bundle parallel links→Eth-Trunk
- Negotiate bundle membership→LACP
Ethernet + VLANs
- MAC learning
- Source MAC + ingress port
- Known unicast
- Forward matching port
- Unknown unicast
- Flood within VLAN
- VLAN
- Separate broadcast domain
- Access port
- One VLAN; untagged
- Trunk port
- Multiple VLANs; mostly tagged
- Hybrid port
- Per-VLAN tag choice
- PVID
- Classifies untagged ingress
- VLANIF
- Layer 3 VLAN gateway
- vlan batch
- Create multiple VLANs
STP vs RSTP
STP
- 802.1D
- Slower convergence
- Five port states
RSTP
- 802.1w
- Faster convergence
- Three port states
Classic vs rapid
STP + Aggregation
- Root bridge
- Lowest bridge ID
- Bridge ID
- Priority + MAC
- Root port
- Best path toward root
- Designated port
- Best path per segment
- Blocked port
- Prevents Layer 2 loop
- RSTP
- Faster STP convergence
- Alternate port
- Backup root path
- Eth-Trunk
- Logical bundled links
- Manual bundle
- Static member selection
- LACP
- Negotiated member selection
Basic vs Advanced ACL
Basic ACL
- Numbers 2000-2999
- Source IPv4 match
Advanced ACL
- Numbers 3000-3999
- Protocol and port match
Source only vs detailed
Security + Service Picker
- Match source IPv4 only→Basic ACL
- Match protocol and ports→Advanced ACL
- One permanent translation→Static NAT
- Many hosts share address→NAPT
- Use interface address→Easy IP
- Publish internal server→NAT Server
- Assign IPv4 settings→DHCP
- Resolve host names→DNS
ACL + AAA + NAT
- Basic ACL
- 2000-2999; source IPv4
- Advanced ACL
- 3000-3999; protocol + endpoints
- traffic-filter inbound
- Filter entering frames
- traffic-filter outbound
- Filter leaving frames
- AAA
- Authentication authorization accounting
- Static NAT
- Fixed one-to-one mapping
- Dynamic NAT
- Public address pool
- NAPT
- Ports share public address
- Easy IP
- Use interface public address
- NAT Server
- Publish inside service
DHCP DORA
Discover Offer Request Acknowledge
D: client discoversO: server offersR: client requestsA: server acknowledges
Services + Ports
- Telnet
- TCP 23; plaintext access
- FTP
- TCP 20/21; file transfer
- TFTP
- UDP 69; simple transfer
- DHCP server
- UDP 67
- DHCP client
- UDP 68
- DNS
- TCP/UDP 53; name resolution
- NTP
- UDP 123; clock sync
- HTTP
- TCP 80; web transfer
- DHCP relay
- Cross-subnet DHCP forwarding
Fit AP vs Fat AP
Fit AP
- Managed by AC
- CAPWAP control
- Central policy
Fat AP
- Standalone management
- Local policy
- No AC required
Centralized vs standalone
WLAN + WAN Picker
- Central AP management→Fit AP + AC
- Standalone AP control→Fat AP
- Local user forwarding→Direct mode
- Central user forwarding→Tunnel mode
- Point-to-point WAN→PPP
- PPP over Ethernet→PPPoE
- Simple password check→PAP
- Challenge-response check→CHAP
WLAN Architecture + Join
- STA
- Wireless client
- AP
- Radio access device
- AC
- Central AP controller
- Fit AP
- AC-managed access point
- Fat AP
- Standalone access point
- SSID
- Wireless network name
- BSSID
- Radio interface identity
- CAPWAP
- AC-to-AP tunnels
- Direct forwarding
- AP sends data locally
- Tunnel forwarding
- AC carries user data
PPPoE Discovery
PADI PADO PADR PADS: discover to session
PADI: initiationPADO: offerPADR: requestPADS: session
PAP vs CHAP
PAP
- Two-way handshake
- Clear credentials
- Weaker
CHAP
- Three-way handshake
- Challenge response
- No clear password
Password vs challenge
PPP + PPPoE + Labels
- PPP
- Point-to-point encapsulation
- LCP
- Establish and test link
- NCP
- Configure network-layer protocols
- PAP
- Two-way clear credentials
- CHAP
- Three-way challenge response
- PPPoE
- PPP over Ethernet
- MPLS
- Label-based forwarding
- Segment Routing
- Source-selected segment list
SNMP + O&M
- NMS
- Management station
- Agent
- Managed device process
- MIB
- Managed object database
- Get
- Read managed object
- Set
- Modify managed object
- Trap
- Unsolicited event notification
- SNMP query
- UDP 161
- SNMP trap
- UDP 162
IPv6 Compression
One :: only; drop leading zeros
Compress longest zero runNever compress twiceKeep eight hextets conceptually
IPv4 ARP vs IPv6 ND
ARP
- IPv4 address resolution
- Broadcast request
Neighbor Discovery
- IPv6 neighbor resolution
- ICMPv6 multicast
Broadcast ARP vs ICMPv6
IPv6 Addressing + Control
- IPv6
- 128-bit addressing
- Hextets
- Eight hexadecimal groups
- ::
- Compress one zero run
- Global unicast
- 2000::/3
- Link-local
- FE80::/10
- Multicast
- FF00::/8
- Loopback
- ::1
- Unspecified
- ::
- IPv6 broadcast
- Does not exist
- Neighbor Discovery
- ICMPv6 replaces ARP
- SLAAC
- RA-based address creation
- ipv6 route-static
- Add IPv6 static route
SDN vs NFV
SDN
- Separates network planes
- Controller-driven policy
NFV
- Virtualizes network functions
- Software appliances
Network control vs functions
SDN + NFV + Python
- SDN
- Separates control and forwarding
- Control plane
- Computes policy and paths
- Forwarding plane
- Moves packets
- Controller
- Centralized network logic
- Northbound API
- Applications to controller
- Southbound API
- Controller to devices
- NFV
- Software network functions
- Automation
- Repeatable network changes
- Python indentation
- Defines code blocks
- Python dictionary
- Key-value collection
Common Traps
MAC vs ARP table
MAC maps port ≠ ARP maps IPv4 to MAC
Prefix vs preference
Longest prefix first ≠ Preference breaks source choice
Root bridge vs root port
One bridge is root ≠ Nonroot selects root port
PVID vs allowed VLANs
PVID classifies untagged ingress ≠ Allowed list permits VLANs
ACL vs NAT
ACL filters traffic ≠ NAT translates addresses
Authentication vs authorization
Authentication proves identity ≠ Authorization grants actions
SSID vs BSSID
SSID names network ≠ BSSID identifies radio
SNMP Get vs Trap
Get is requested ≠ Trap is unsolicited
IPv6 compression
Leading zeros freely omitted ≠ Double-colon used once
SDN vs automation
SDN changes architecture ≠ Automation repeats operations
Last Minute
- 1.Domains 1-5: 8,27,28,8,5
- 2.Domains 6-10: 10,3,3,5,3
- 3.Longest prefix before preference
- 4.Lower route preference wins
- 5.OSPF backbone equals area zero
- 6.Access one VLAN; trunk many
- 7.Lowest bridge ID becomes root
- 8.Basic ACL source; advanced detailed
- 9.AAA: authenticate, authorize, account
- 10.DHCP follows DORA
- 11.Fit AP obeys AC
- 12.PPP: LCP, authentication, NCP
- 13.IPv6 ND replaces IPv4 ARP
- 14.SDN separates control and forwarding
- 15.VRP save persists configuration
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