DCNP flashcards
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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 data center fabric where every leaf switch connects to every spine switch, and no leaf-to-leaf or spine-to-spine links exist. It provides predictable latency and equal-cost multipath.
- Oversubscription ratio
- The ratio of host-facing bandwidth to uplink bandwidth at a switching tier. A 3:1 ratio means hosts can collectively demand three times the available northbound capacity.
- North-south vs east-west
- North-south traffic enters or leaves the data center through the core or edge. East-west traffic moves between servers inside the data center and usually dominates volume in modern designs.
- Fat-tree k-ary fabric
- A Clos-style topology with k pods, (k/2)^2 core switches, and k^2/2 aggregation plus k^2/2 edge switches, supporting k^3/4 hosts with full bisection bandwidth.
- Top-of-rack switching
- An access switch placed inside each rack, connecting servers to the fabric over short cables. It simplifies rack-level changes but increases the number of managed devices.
- 802.1Q VLAN tag
- A four-byte tag inserted into Ethernet frames carrying a 12-bit VLAN identifier, giving 4094 usable VLANs. Untagged traffic belongs to the native VLAN on a trunk.
- RSTP port roles
- Rapid Spanning Tree defines root, designated, alternate, and backup roles. Alternate and backup ports are discarding and provide fast failover without timer-based convergence.
- LACP port-channel hashing
- Link aggregation distributes traffic across member links by hashing flow fields. A single flow always uses one member link, so it cannot exceed that link's bandwidth.
- BGP best-path order
- Selection order begins with highest weight, then highest local preference, then locally originated routes, then shortest AS-path, then lowest origin, then lowest MED, then eBGP over iBGP.
- Equal-cost multipath
- ECMP installs multiple equal-metric next hops for a destination and hashes each flow to one path, increasing bandwidth and resilience while preserving per-flow ordering.
- VXLAN VNI
- A 24-bit VXLAN Network Identifier that scopes an overlay segment, supporting about 16 million segments compared with roughly 4,000 VLANs.
- VXLAN VTEP
- A VXLAN tunnel endpoint that encapsulates frames from a local segment into UDP packets and decapsulates traffic arriving from remote endpoints. The underlay must route between VTEP loopbacks.
- EVPN route type 2
- An EVPN MAC/IP advertisement route that distributes endpoint MAC addresses and optionally IP addresses across the fabric, enabling control-plane learning and ARP suppression.
- SDN control plane separation
- Software-defined networking moves forwarding decisions to a centralized controller and keeps packet forwarding in the data plane, enabling global policy but adding a controller dependency.
- NETCONF and YANG
- NETCONF is an XML-based configuration protocol operating on YANG-modeled datastores with commit and rollback. RESTCONF offers the same models over HTTP with JSON or XML.
- Streaming telemetry
- A push model where network devices send structured, model-driven data (often over gNMI or gRPC) at short intervals, giving higher fidelity than interval-based SNMP polling.
- Network function virtualization
- NFV runs network services such as firewalls and load balancers as virtual machines or containers on commodity hardware, replacing dedicated appliances and enabling service chaining.
- Intent-based networking
- A declarative approach where operators state the desired end state, software compiles it into device configuration, and closed-loop verification compares actual state to intent.
- VRF segmentation
- A Virtual Routing and Forwarding instance maintains a separate routing table on a device, isolating tenant or security-zone reachability. VRFs isolate control plane; ACLs or firewalls filter data.
- 802.1X components
- Port-based access control uses a supplicant on the host, an authenticator switch, and a RADIUS authentication server. EAP-TLS uses certificates; PEAP/MSCHAPv2 uses passwords.
- MACsec versus IPsec
- MACsec (802.1AE) encrypts Layer 2 hop by hop between adjacent devices. IPsec encrypts Layer 3 end to end, with ESP providing confidentiality and AH providing integrity only.
- DHCP snooping and DAI
- DHCP snooping builds a trusted binding of MAC, IP, port, and VLAN. Dynamic ARP inspection validates ARP packets against that table, blocking spoofed gateway attacks.
- Microsegmentation
- A zero-trust technique enforcing per-workload policy regardless of network location, typically through security groups or distributed firewalls rather than perimeter-only controls.
- Idempotent automation
- A property where applying the same automation repeatedly produces the same end state. Declarative tools such as Ansible modules and Terraform resources are idempotent by design.
- Ansible versus Terraform
- Ansible is agentless, SSH-based, YAML-driven, and push-based. Terraform tracks resources in a state file and uses plan/apply against provider APIs, suiting cloud and infrastructure provisioning.
- REST HTTP methods
- GET reads a resource, POST creates, PUT replaces, PATCH partially updates, and DELETE removes. Common status codes include 200, 201, 400, 401, and 404.
- Configuration drift
- A divergence between the running device configuration and the intended source of truth. It is detected by periodic collection or telemetry and remediated by reapplying declarative intent.
- VXLAN MTU overhead
- VXLAN adds 50 bytes over IPv4 (outer IP, UDP, VXLAN, and inner Ethernet headers). The underlay MTU must be raised to at least 1550 to avoid fragmentation or drops.
- Interface CRC errors
- A rising count of CRC or input errors on an interface indicates Layer 1 problems such as bad cabling, faulty optics, or duplex mismatch, not a routing or policy issue.
- Syslog severity levels
- Syslog levels run from 0 (emergency) through 7 (debug), where a lower number means higher severity. Level 4 is warning; level 6 is informational.
- BGP session states
- BGP progresses through Idle, Connect, Active, OpenSent, OpenConfirm, and Established. Troubleshooting checks session state, prefix receipt, best-path selection, then RIB and FIB installation.
- MTTR and availability
- MTTR is mean time to repair and MTBF is mean time between failures. Availability equals MTBF divided by the sum of MTBF and MTTR, so reducing repair time raises availability.