Topics
| Stream | Topics | % Done |
|---|---|---|
| Networking | OSI layers | 100% |
| TCP, IP, UDP, ICMP, ARP, DHCP, NAT, FTP | 100% | |
| HTTP, SSL | 100% | |
| Caching, Cookies, Certificates | Caching, Cookies, | |
| DNS | Done | |
| SMTP | ||
| Latency, Tail Latency | ||
| BGP, OSPF | Done | |
| Load Balancing | ||
| Linux | Shell scripting | |
| Kernel, libraries, system calls | Done | |
| Memory Management | ||
| Permissions, file systems | Done | |
| Linux Commands Brushup | Done | |
| Programming | Python Brushup | |
| Algorithms | ||
| HTML, CSS | ||
| Databases, SQL, Indexing | ||
| Technical Quesitions | ||
| Behavioral Questions | ||
| Leadership Questions | ||
| Designing | Medium sized Campus Design | |
| Cheatsheet | Done |
Preparations
- 1st round
- 1st Week Dec starting
- Video interview
coding tech communication thinking
- 1 Hour:
1st Troubleshooting code Distributes system Web & Network technologies
- F2F - Bangalore office
2 tech Networking/General Web troubleshooting 1 manager
- Share use cases
- Working with Code (15 min)
- What is code, Issue & How to improve it.
- Ask question about question
- Break it down
- No IDE
- No library
Topics 2
- Semaphores
- Mutex
- Threads
Questions
- What are alternative solutions of Spanning tree?
Port Isolation Vlan Isolation Loopback Detection
- Tail Latency
200ms latency -> initial rto by most OSs Do not consider normal Retransmissions, but only RTOs exponential backoff rto will double with each iteration -> 400ms, 800ms, 1000ms congestion, pathmtu not honored, icmp rate-limited, reply pathmtud-reply packets dropped, os issues -> Zero window -> cpu high(response slow), memory high, disk issue
- 4k video file edit latency
RTP uses tcp, n/w level issues, check latency on which side traces,
Networking Followup
- 1) Moving of files BW APAC & EMEA
1MBPS speed? whats wrong Multiple streams Pearing Latency Congestion BW/Delay product BDP TCP Window size Packet capture
- 2) SSH to remote server
GCP VM Timed out
- 3) System Design
Past system design you have done Trade off you made in this Scaling this specific network 3-tier network design in public cloud. How do you diesgn Will you need LB? Why?
- 4) How can you establish secure connectivity to public cloud
VPN tunnel? How do you ensure High Availabiltiy for this?
- 5) Re-Evaluate the design?
Room for improvement?
- Answers
- 1)
- Network throughput impacted by TCP window size, Latency and Congestion
- Window Size
Maximum amount of data a sender can send before receiving an acknowledgement. Standard TCP Window Size = 65K bytes
- Bandwidth Delay Product
Amount of data that can be in transit (flight) in the network Includes data in queues if they contributed to the delay BDP (bytes) = total_available_bandwidth (bps) x round_trip_time (sec) / 8
Take Packet Captures Fragmentation WSF 64kB to 8MB SACK to minimize data that is resent Fast re-transmits to reduce delay before resend
- BIC TCP for faster recovery from packet loss
Allows bandwidth probing to be more aggressive initially when the difference from the current window size to the target window size is large, and become less aggressive as the current window size gets closer to the target window size. A unique feature of the protocol is that its increase function is logarithmic; it reduces its increase rate as the window size gets closer to the saturation point.
- It’s not just about latency, TCP doesn’t like congestion
Adding more traffic produces a negative marginal effect above about 30% utilization
- Window scaling changes the TCP window to:
64KB * 2n (n = window scale factor)
With a window scale factor of 7, which equals a TCP window of 8MB
Single-flow throughput is limited to: TCP window size / RTT
Without window scaling, TCP is limited to: 64KB / 100ms = 5 Mbps
With CloudBridge default window scale, TCP is limited to: 8MB / 100 ms = 650 Mbps
- Application is able to generate 10 GBPS traffic? OS limits - CPU - Memory, Network Card speed?