Cisco CCNA (200-301) - IP Subnetting, VLANs & Routing Protocols Flashcards

Question 1

IPv4 Subnetting: Usable Hosts Formula

Accepted Answer

The formula to calculate the number of usable host IP addresses in a subnet is $2^h - 2$, where $h$ is the number of host bits remaining in the subnet mask. Subtract 2 to account for the **Network ID** and **Broadcast Address**.

Question 2

CIDR Prefix `/28`: Subnet Mask & Usable Hosts

Accepted Answer

A `/28` prefix length corresponds to the subnet mask `255.255.255.240`.
- **Total IP Addresses:** $2^4 = 16$
- **Usable Host Addresses:** $16 - 2 = 14$
- **Block Size (Magic Number):** $256 - 240 = 16$

Question 3

Administrative Distance (AD)

Accepted Answer

A trustworthiness rating from 0 to 255 assigned to a routing source. Routers use AD to select the best path when multiple routing protocols learn the exact same prefix. **Lower AD is preferred**.

Common AD Defaults:
- Connected: `0`
- Static: `1`
- eBGP: `20`
- OSPF: `110`
- RIP: `120`

Question 4

Administrative Distance vs. Routing Metric

Accepted Answer

- **Administrative Distance (AD):** Used to select between different routing protocols supplying a route to the *same prefix*.
- **Metric:** Used to select the best path *within* a single routing protocol (e.g., OSPF Cost, RIP Hop Count).

Question 5

Longest Prefix Match Rule

Accepted Answer

The fundamental routing table lookup rule where the router selects the entry with the **most specific (longest) subnet mask** matching the destination IP address, regardless of Administrative Distance or Metric.

Question 6

IEEE 802.1Q Frame Tagging

Accepted Answer

The standard protocol for VLAN trunking that inserts a 4-byte header into the standard Ethernet frame. It contains a 12-bit **VLAN Identifier (VID)** field, supporting up to $2^{12} - 2 = 4,094$ usable VLAN IDs.

Question 7

Native VLAN Functionality

Accepted Answer

An 802.1Q VLAN designated to carry **untagged traffic** across a trunk link. Frames belonging to the Native VLAN do not receive an 802.1Q tag. Both ends of a trunk must have matching Native VLAN configurations to prevent VLAN leaking.

Question 8

Dynamic Trunking Protocol (DTP) Modes

Accepted Answer

- `access`: Forces the interface into permanent non-trunking mode.
- `trunk`: Forces the interface into permanent trunking mode.
- `dynamic auto`: Converts to trunk if the neighboring interface is set to `trunk` or `desirable`.
- `dynamic desirable`: Actively solicits the link to convert into a trunk.

Question 9

Command: Configure an 802.1Q Trunk Port

Accepted Answer

```text
interface GigabitEthernet0/1
 switchport mode trunk
 switchport trunk native vlan 99
 switchport trunk allowed vlan 10,20,30
```

Question 10

OSPF Hello and Dead Timers (Broadcast Networks)

Accepted Answer

By default on multi-access broadcast networks:
- **Hello Timer:** 10 seconds
- **Dead Timer:** 40 seconds ($4 	imes 	ext{Hello}$)

*Note:* Timers must match identically between neighbors to form an adjacency.

Question 11

OSPF Neighbor States (Sequential Order)

Accepted Answer

1. **Down**
2. **Init**
3. **2-Way** (DR/BDR elected on multi-access networks)
4. **ExStart**
5. **Exchange**
6. **Loading**
7. **Full** (Fully synchronized link-state database)

Question 12

OSPF 2-Way State Significance

Accepted Answer

Indicates bi-directional communication is established (a router sees its own Router ID in the neighbor's Hello packet). On non-DR/BDR interfaces, neighbors remain in `2-Way` state permanently.

Question 13

OSPF Cost Metric Formula

Accepted Answer

$$	ext{Cost} = \frac{	ext{Reference Bandwidth}}{	ext{Interface Bandwidth}}$$

Default reference bandwidth is $10^8	ext{ bps}$ ($100	ext{ Mbps}$). The cost of a route is the cumulative sum of egress interface costs along the path.

Question 14

Command: Configure Single-Area OSPFv2

Accepted Answer

```text
router ospf 1
 router-id 1.1.1.1
 network 192.168.1.0 0.0.0.255 area 0
```
*Alternative method (interface level):*
```text
interface GigabitEthernet0/0
 ip ospf 1 area 0
```

Question 15

Router-on-a-Stick (ROAS) Configuration

Accepted Answer

Configuring subinterfaces on a single physical router interface to perform Inter-VLAN routing:
```text
interface GigabitEthernet0/0.10
 encapsulation dot1Q 10
 ip address 192.168.10.1 255.255.255.0
```

Question 16

IPv6 Global Unicast Address (GUA) Subnetting

Accepted Answer

A standard IPv6 GUA uses a `/48` Global Routing Prefix assigned by an ISP. The next 16 bits form the **Subnet ID** (bits 48–63), creating $2^{16} = 65,536$ subnets with a default host prefix of `/64`.

Question 17

IPv6 Link-Local Address Characteristics

Accepted Answer

- **Prefix Range:** `fe80::/10` (typically `fe80::/64`)
- Automatically configured on IPv6-enabled interfaces.
- Non-routable; valid only within the local layer 2 segment (link).

Question 18

Command: Display IP Routing Table

Accepted Answer

Use `show ip route` for IPv4 or `show ipv6 route` for IPv6.

Displays codes for route sources (e.g., `C` = Connected, `S` = Static, `O` = OSPF), along with AD, metric, and next-hop address.

Question 19

Floating Static Route

Accepted Answer

A backup static route configured with a higher Administrative Distance than the primary routing protocol or primary static route.

Example:
`ip route 10.0.0.0 255.0.0.0 192.168.1.2 130`
*(AD set to 130, higher than OSPF's 110)*

Question 20

Passive Interface in OSPF

Accepted Answer

Configured with `passive-interface <interface>` inside the OSPF configuration mode. It stops sending and receiving OSPF Hello packets on that interface, preventing neighbor adjacencies while still advertising the interface's connected subnet into OSPF.

Cisco CCNA (200-301) - IP Subnetting, VLANs & Routing Protocols

Cards in this deck

Related Flashcard Sets

Korean TOPIK I Level 2 - Core Vocabulary & Sentence Structure

Machine Learning - Supervised Learning & Ensemble Methods

Azure Administrator (AZ-104) - Core Infrastructure & Services

JLPT N4 - Essential Kanji & Grammar