JNCIA-DC flashcards
JNCIA-DC · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Spine-leaf topology
- A two-tier Clos fabric where every leaf switch uplinks to every spine switch. Leaves never interconnect, spines never interconnect, so any server-to-server path is exactly leaf-spine-leaf with constant latency.
- Oversubscription ratio
- Total downlink bandwidth divided by total uplink bandwidth on a switch tier. A 1:1 ratio is non-blocking; 3:1 means uplinks carry only one third of aggregate host demand at full load.
- East-west traffic
- Traffic that stays within the data center, such as server-to-server application calls, storage replication, and live VM migration. It dominates modern data center load compared with north-south client traffic.
- North-south traffic
- Traffic that crosses the data center boundary, entering from or leaving to clients, WAN links, or the internet. It typically passes through border routers and firewalls rather than staying on the fabric.
- VXLAN VNI
- A 24-bit VXLAN Network Identifier that tags encapsulated Layer 2 frames, allowing roughly 16 million segments. It replaces the 12-bit VLAN ID limit of 4094 segments.
- VXLAN UDP port
- VXLAN encapsulates original Ethernet frames inside UDP datagrams sent to destination port 4789. The outer IP header carries the tunnel endpoints, and the VNI identifies the segment.
- EVPN route type 2
- An EVPN MAC/IP advertisement route. It distributes host MAC addresses and optionally IP addresses through MP-BGP, enabling control-plane MAC learning instead of data-plane flooding.
- Anycast gateway
- A distributed IRB design where every leaf uses the same gateway IP and MAC address. A host keeps its default gateway after migrating, and routing happens at the first leaf.
- MC-LAG
- Multi-chassis link aggregation lets a server dual-home to two independent switches that act as one LAG endpoint. Both links forward traffic, avoiding the STP blocking of one link.
- Junos control and forwarding planes
- The Routing Engine runs routing protocols and builds the forwarding table; the Packet Forwarding Engine forwards packets using that table. A control-plane restart can occur without stopping forwarding.
- commit confirmed
- A commit that automatically rolls back after a specified number of minutes unless confirmed by another commit. It protects remote changes that could otherwise lock out the administrator.
- commit check
- A command that validates the candidate configuration syntax and semantics without applying it. It reports errors so problems are found before an actual commit.
- rollback 1
- A configuration-mode command that loads the previous committed configuration into the candidate. Rollback 0 loads the currently active configuration, and up to 50 prior versions are stored.
- display set
- A pipe option, show | display set, that renders the configuration as flat set commands. It is useful for copying, comparing, or scripting configuration changes.
- Rescue configuration
- A saved known-good configuration created with request system configuration rescue save. It can be restored later with rollback rescue when a change breaks the device.
- Junos login classes
- Permission profiles assigned to users, including super-user, operator, read-only, and unauthorized. The class determines which commands and configuration hierarchies a user may access.
- IRB interface
- An integrated routing and bridging interface that provides a Layer 3 gateway for a VLAN. It is bound to the VLAN with the l3-interface statement, enabling inter-VLAN routing.
- Trunk interface mode
- An ethernet-switching port mode carrying multiple VLANs, configured with vlan members. An optional native-vlan-id sends untagged frames into a specified VLAN.
- LACP active mode
- A link aggregation setting where the local side actively sends LACP packets to negotiate the bundle. Members are added with ether-options 802.3ad, and the bundle is an ae interface.
- show ethernet-switching table
- An operational command listing learned MAC addresses, their VLANs, and the interfaces where they were learned. It verifies Layer 2 forwarding and detects MAC moves.
- show log messages
- An operational command displaying system log entries, including interface state changes, protocol events, and errors. It is a primary first step when troubleshooting unexpected behavior.
- monitor traffic interface
- An operational command that captures and displays live packets on an interface, similar to tcpdump. It is used to confirm whether traffic actually arrives or leaves.
- Zero Touch Provisioning
- A boot process where a factory-default device obtains an IP address and configuration file automatically, often via DHCP options. It brings new switches into service without manual setup.
- request system zeroize
- A command that erases configuration and data and returns the device to factory default. It is used before decommissioning or repurposing hardware.
- Junos route preference
- A value where lower wins. Connected is 0, static 5, OSPF internal 10, RIP 100, OSPF external 150, EBGP 170, and IBGP 200, deciding which protocol installs a route.
- Routing policy term
- A policy building block with from conditions and then actions such as accept, reject, or next term. Terms are evaluated top-down, and the first terminating match decides.
- Import versus export policy
- Import policy filters routes before they enter the routing table. Export policy filters which routes are advertised to neighbors. Both are referenced from protocol statements.
- IBGP full mesh
- IBGP peers do not re-advertise routes learned from other IBGP peers, so every peer must connect directly or use a route reflector. A full mesh avoids split-horizon black holes.
- Firewall filter implicit discard
- A stateless firewall filter with no matching term applies an implicit discard to the packet. An explicit then accept term is required for permitted traffic.
- Firewall filter application
- Filters are applied per interface and direction, such as family inet filter input F. Input filters inspect traffic entering the interface; output filters inspect traffic leaving it.
- show ospf neighbor
- An operational command listing OSPF adjacencies and their states. A state of Full indicates the adjacency has converged and database synchronization is complete.
- show route detail
- An operational command showing a prefix's protocol, preference, next hop, and policy information. It confirms which route was selected and why.