20 topics
Computer networks help, including subnetting you can do without the calculator
Subnetting exam questions are answered in binary or not at all. A mask of /26 means 26 bits are network, leaving 6 for hosts, which gives blocks of 64 addresses: 0, 64, 128, 192. Once you can produce that block size from the prefix in your head, the network address, the broadcast address and the usable range all follow in about fifteen seconds without a calculator you are not allowed to bring anyway.
Where students get stuck
I cannot work out a subnet range under exam pressure
Go through the prefix, not the dotted mask. Subtract the prefix from 32 to get host bits, then the block size is 2 raised to that power. A /27 leaves 5 host bits, so blocks of 32: 0, 32, 64, 96 and so on in the last octet. Your address falls inside one of those blocks; the bottom of the block is the network address, the top is the broadcast, and everything between is usable, which is block size minus 2. For prefixes below /24 the same arithmetic just moves into the third octet.
I never know whether something is TCP or UDP
Ask what the application does when a packet goes missing. If a missing piece corrupts the result — a file, a web page, an email — it needs TCP, which numbers segments, acknowledges them and retransmits what is lost, at the cost of waiting. If a late piece is worse than a missing one — live voice, video calls, gaming, DNS lookups — it uses UDP, because a retransmitted syllable arriving after the conversation moved on is useless. TCP buys reliability and ordering with latency, and that trade is the whole answer.
Ping works but the website will not load
Ping proves the route and basic connectivity, so the failure is above that. Ping the site by IP address rather than name: if the IP works and the name does not, name resolution is the problem, so check the DNS server your machine was handed. If both fail, the server may be up but blocking ICMP, or filtering traffic on port 443 while leaving ping alone. Working up the layers in that order — link, then address, then name, then port — turns a vague outage into one specific broken step.
DHCP and DNS keep getting mixed up
They answer different questions at different moments. DHCP runs when a device joins a network and hands it an address to use, plus the gateway and the addresses of DNS servers; without it you would configure each machine by hand. DNS runs every time you use a name, translating something readable into the address packets need. So DHCP tells your laptop who it is, DNS tells it where everyone else is. A DHCP failure means no address at all; a DNS failure means an address that works only if you already know the numbers.
Everyone at home has the same IP address, and I do not understand why
Those internal addresses in the 192.168 or 10 ranges are private, reserved for reuse inside any network and not routable across the internet. Your router performs NAT: it rewrites the source address of outgoing packets to its single public address, records the internal address and port in a translation table, and reverses the swap on the way back. That is why an incoming connection needs port forwarding to be told which internal machine to reach, and why address exhaustion in IPv4 was survivable long enough for IPv6 to arrive.
What's covered
Computer Networks topics you can work through with a tutor, generate practice on, or turn into flashcards and a study plan.
Models and layers
- The OSI seven layers and what belongs at each
- The TCP/IP model and how it maps onto OSI
- Encapsulation, headers, and the frame-packet-segment vocabulary
- Protocol data units and MTU
Addressing and routing
- IPv4 addressing, classes, and CIDR notation
- Subnetting, VLSM, and calculating usable hosts
- IPv6 addressing and abbreviation rules
- ARP, MAC addresses, and switch forwarding tables
- Routing tables, static routes, and distance-vector versus link-state
- NAT, private address ranges, and port forwarding
Transport and applications
- TCP three-way handshake, sequence numbers, and teardown
- Flow control, sliding windows, and congestion control
- UDP and when unreliable delivery is correct
- Ports, sockets, and well-known port numbers
- HTTP, DNS, DHCP, SMTP, and FTP behaviour
Physical, wireless, and security
- Cabling, collision domains, and switches versus hubs
- VLANs and trunking
- Wi-Fi standards, channels, and interference
- TLS, firewalls, and access control lists
- Packet capture and reading a Wireshark trace
Computer Networks questions
Can it drill subnetting until it becomes automatic?
Yes, and that is the right way to use it for this topic. Practice quizzes generate fresh addresses and prefixes each round and return full worked solutions, so when you get a broadcast address wrong you see which step of the block arithmetic went astray rather than just a red mark.
I have a Wireshark capture I do not understand. Can it look at it?
Share your screen with the capture open and it reads the packet list and the expanded headers with you. Most of the difficulty there is knowing which columns matter and what a retransmission or a reset actually indicates, which is easier to explain against your real trace than in the abstract.
Is this aligned to a certification like Network+ or CCNA?
The topics overlap heavily, and it will follow whatever objective list you give it. Be aware that vendor certifications have their own terminology and their own preferred answers, so tell it which exam you are sitting and stay inside that vocabulary rather than the generic one.
Can it help with router configuration commands?
It can walk through what a configuration does and why an interface stays down, and it is genuinely useful for reading a running configuration line by line. It has no access to your equipment or simulator, so you type the commands and describe or share what came back.
Stuck on computer networks right now?
Talk it through out loud, share your screen, and watch it worked out step by step on a whiteboard.
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