Intrvw

AMZN Networking

Round 1

• BGP Route manupulation

Directions?

• Anycast
• Linux check WSF
• SSL speed up at LB level:

 Session Ticket
 OSPC Stapling

• Cookie Uses
• Google BBR - congestion control algorithm
• DNS check if reply is spoofed or not?
• How does DNS client knows when to switch to TCP?

TC Flag

Round 2

• Experience with diffcult customer
• Learnt from feedback

Windows

• How to remotely access Windows server?

RDP, VNC (Teamviewer, Webex for PC)
RDP Port no
TCP port 3389 and UDP port 3389

• Page file
• Service
• Service fails, how to check logs? (Event logs viewer)

Linux

• Kernel
• Inode
• Check CPU, Memory, HDD info?
• Check Load Average? What is the output?(1,5,15 min avrg), what does it mean?
• Check Clients we are connected to? netstat -ant -> Foreign Address
• ifconfig -a - eth0:1 - What does :1 mean? (vlan)
• Check file in use by which process? lsof
• Runlevels
• Check DNS config? /etc/resolv.conf & interface config
• Iptables?

Networking

• NAT
• How does Traceroute works?
• Request & response headers

curl -v http://google.com

• Commands used in daily troubleshooting

telnet 
nc 
ipconfig
netstat
traceroute
top
ps
free
df
dh

Scenario

[PC]---------[Website]
1st attempt - 404
2nd attempt - 200
3rd attempt - 404
4th attempt - 200
LB having 2 servers, one is not having app installed, check logs & disable it.

Round 4 - Architecture

• Explain case you have worked - Voip CB Repro
• Design a Ecommerse website with full redundancy, explain protocols used:

  - Avi SE scaling, use 3 node cluster for controller
  - Use 2 AZs
  - How DB will sync
  - GSLB usage - geodb Networking
  - how persistence will work
  - Storage redundancy
  - Storage slow, use SSD
  - Pics load slowly in Japan

Round 5 - Linux

• Boot process in detail
• What is kernel? How does it communicate with HW/User? System calls
• Name the various System calls
• What is initrd ? What it contains/does ? (drivers to load disk,etc)
• Runlevels
• Upstart/Systemd
• What is Swap?
• How to find swap usage?
• How to find if a file is moving from RAM to SWAP? iotop(process wise usage) & iostat(part wise usage)
• How to check processes using most CPU/How to check CPU usage per core?
• Process States:

   - Stop   (my answers)
   - Start
   - Running
   - Sleeping  ==> Interupptable waiting/ uninterruptable waiting -> Explain each
   - Killed
   - Zombie

• Type of File systems - FAT32/ExFAT, NTFS, EXT3, EXT4
• How to use a brand new disk in Linux machine

- Format
- Partition
- Mount

• What are permissions -> 640?

 6 -> user      - Read/Write
 4 -> group   - Read
 0 -> Others - None

• How to check Memory usage - top//free -m // cat /proc/meminfo

  - Buffer/Cache field?
  - Swap field?

• How to troubleshoot if a file stopped coping in between saying no disk space, but disk space is there.

 df -h => check free disk space
 df -i  => Free inodes check

• What is inode? How can they get full(mail server; large no of empty files)?

Round 6 - Networking

• Design a website for 500 Employees - use 2 AZs?
• Troubleshoot a website not reachable?

curl -I,   telnet,    nc,    ping

• How to check if DNS is working or not?

dig @42.2.2 google.com

• Check packet captures using tcpdump.
• Explain DNS resolution in Full details.
• Troubleshooting a slow website:

Top  --> CPU, Memory,  Process usages, Load avg
df -h  --> Disk usage
free -m
cat /proc/meminfo
netstat -ant
cpu ==> 0 "us" user space
top -o %CPU

• Explain TCP Window? How it can be full
• OSPF vs BGP? why not use OSPF for Internet instead of BGP?
• OSPF packet types?

   Hello
   DBD
   LSR
   LSU [LSAa]
   LSAck

• What is Area 0 in OSPF?
• BGP Attributes
• BGP getting more traffic from one ISP than other? How to balance that?
• What is DDOS attack? How to mitigate it?

Need to know about the type of attack
Syn Flood attack can be mitigate by using Syn-Cookie

• What is Syn-Cookie used for?

Round 7

• Repro Attempt
• Something not done within committed time
• Something done differently from a colleague
• Something you have done apart from regular work
• Tough Feedback received; What you did about it.