LCPE flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- OSI model layers
- Seven layers from bottom: Physical, Data Link, Network, Transport, Session, Presentation, Application. Each layer provides services to the layer above and communicates logically with its peer layer on the remote device.
- TCP three-way handshake
- Client sends SYN, server replies SYN-ACK, client sends ACK. This establishes sequence numbers and confirms bidirectional reachability before data transfer begins.
- Private IPv4 address ranges
- 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 are non-routable on the internet and require NAT for external communication. 169.254.0.0/16 is link-local APIPA.
- IPv6 link-local address
- Automatically generated in fe80::/10 on every IPv6-enabled interface. Used for neighbor discovery and next-hop addressing; never routed beyond the local link.
- Default gateway function
- The router address a host uses when the destination is outside its local subnet. The host ARPs for the gateway MAC and forwards the frame to it.
- VLAN trunk 802.1Q
- A trunk carries multiple VLANs over one link. Each frame gets a 4-byte tag containing a 12-bit VLAN ID; the native VLAN is sent untagged.
- Spanning Tree root bridge
- The switch with the lowest bridge ID (priority then MAC) becomes root. All its ports are designated and forwarding; other switches elect one root port each.
- STP port states
- Classic 802.1D: blocking, listening (15 s), learning (15 s), forwarding, disabled. RSTP reduces these to discarding, learning, and forwarding for faster convergence.
- EtherChannel LACP modes
- Active actively negotiates; passive waits. At least one side must be active. Mismatched speed, duplex, or VLAN configuration prevents the bundle from forming.
- Port security violation modes
- Protect drops offending frames silently; restrict drops and logs; shutdown puts the port in err-disabled state and requires manual recovery.
- Wireless non-overlapping channels
- In 2.4 GHz only channels 1, 6, and 11 do not overlap. The 5 GHz band offers many non-overlapping channels, reducing co-channel interference in dense deployments.
- Administrative distance values
- Trustworthiness ranking: connected 0, static 1, eBGP 20, EIGRP 90, OSPF 110, RIP 120. Lower values are preferred when multiple protocols offer the same prefix.
- Longest prefix match
- When multiple routes match a destination, the router selects the most specific prefix (largest mask length), regardless of administrative distance or metric.
- Floating static route
- A static route configured with an administrative distance higher than the primary dynamic route. It stays out of the table until the primary route fails.
- OSPF neighbor requirements
- Neighbors must share area ID, hello and dead timers, subnet and mask, authentication, and MTU. Router IDs must be unique for adjacency to form.
- OSPF DR and BDR election
- On multiaccess networks, highest interface priority wins, then highest router ID. Priority 0 excludes an interface. The DR reduces adjacency count and LSA flooding.
- EIGRP feasible successor
- A backup route whose reported distance is lower than the current feasible distance. It can be installed immediately if the successor fails, avoiding active-state queries.
- Router-on-a-stick
- A single router interface split into subinterfaces, each with encapsulation dot1q and an IP address per VLAN, providing inter-VLAN routing over one trunk link.
- HSRP virtual MAC address
- HSRP group addresses use 0000.0c07.acXX, where XX is the group number in hex. VRRP uses 0000.5e00.01XX instead.
- DHCP DORA process
- Discover (broadcast), Offer (server proposes address), Request (client accepts), Acknowledge (server confirms lease). Client uses UDP 68; server uses UDP 67.
- DHCP relay agent
- The ip helper-address command on a router interface forwards broadcast DHCP requests to a server on another subnet as unicast, enabling centralized DHCP.
- NAT terminology
- Inside local is the private source before translation; inside global is the translated public address; outside global is the destination's public address on the internet.
- PAT overload
- Port Address Translation maps many inside hosts to one public IP, distinguishing sessions by source port. Configured with the overload keyword on a NAT statement.
- Syslog severity levels
- 0 emergency, 1 alert, 2 critical, 3 error, 4 warning, 5 notice, 6 informational, 7 debugging. Lower numbers are more severe; default logging is level 6.
- NTP stratum
- Stratum 0 is a reference clock; stratum 1 servers attach directly. Each hop increases stratum by one; lower stratum is preferred and stratum 16 means unsynchronized.
- QoS DSCP EF
- Expedited Forwarding, decimal 46, marks voice traffic for low latency, low jitter, and minimal loss. It is a 6-bit Layer 3 field in the IP header.
- Standard versus extended ACL
- Standard ACLs filter on source address only and belong near the destination. Extended ACLs filter protocol, source, destination, and ports, and belong near the source.
- ACL wildcard mask
- The inverse of a subnet mask, used to specify which address bits must match. A 0 bit means match; a 1 bit means ignore. Every ACL ends with an implicit deny.
- DHCP snooping
- Blocks DHCP offers from untrusted ports to prevent rogue servers. Trusted ports face the legitimate server or uplink; client ports remain untrusted.
- TACACS+ versus RADIUS
- TACACS+ uses TCP 49, encrypts the entire payload, and separates AAA functions. RADIUS uses UDP and encrypts only the password, commonly for network access.
- IPsec AH and ESP
- AH provides integrity and authentication but no encryption. ESP provides confidentiality plus integrity, and is the standard choice for site-to-site VPN tunnels.
- REST API CRUD verbs
- POST creates, GET reads, PUT or PATCH updates, DELETE removes. REST is stateless, so each request carries all information needed to process it.