Network Security Wiki

Intrvw

Revision as of 04:32, 22 June 2021 by Amanjosan2008 (talk | contribs) (→‎Dell)

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 3 - Behavioral

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.

AMZN DMS

1st Round Online Challenge
Telephonic Round
Tell me something where you did something extra during a case/your job
Tell me something where you learned something during a case/your job
Where do you store your code(Github)? How can some one other edit code?
How DNS works? Explain in detail.
DNS traffic Flow? Search local cache > hosts file > DNS server
What is VoIP? How SIP works?
Scenario:
  [LB]------[srv1][srv2][srv3]srv4]
  Srv3 is slow, latency, how to troubleshoot? top, free -h, df -h
  How to check traffic requests coming per second? netstat -s, ss -s, tcpdump

Google

Challenge

CouchBase

  • OOM Killer
  • Page Fault
A page fault (sometimes called #PF, PF or hard fault) is a type of exception raised by computer hardware when a running program accesses a memory page that is not currently mapped by the memory management unit (MMU) into the virtual address space of a process.
  • Swap Memory
  • DNS Rate Limiting Troubleshoot
Create Static entry
Increase Cache Time
  • DNS latency in Server or Network Troubleshoot:
Check RTT for other traffic & DNS Specific traffic.
  • Print below logs:
startTime : 12332121324
endTime : 21342313222
serviceName : abc
status : 200
------------------------
startTime : 12332121324
endTime : 21342313222
serviceName : abc
status : 200
------------------------
startTime : 12332121324
endTime : 21342313222
serviceName : abc
status : 200
------------------------
startTime : 12332121324
endTime : 21342313222
serviceName : abc
status : 200
------------------------
startTime : 12332121324
endTime : 21342313222
serviceName : abc
status : 200
------------------------
  • My Solution:
f=open('text.txt','r')
l=f.readlines()

a=[]

for i in l:
if ":" in i:
a.append((i.strip('\n')).split(':'))

b=[]
for i in range(len(a)):
b.append(a[i][0])

b=set(b)

for i in b:
print(i,end='')

for i in range(len(a)):
if "startTime " in a[i]:
print(a[i][1],a[i+1][1],a[i+2][1],a[i+3][1],end='')
print('\n', end="")

Juniper

Is UDP Stateful
How is UDP connectionless
FTP types
What is Frag Offset
IKE v1 vs IKE v2

Dell

Vpn support multicat,broadcst
dhcp across vpn, firewall interfaces in diff subnets
traffic shapping
fragmentation
ssl

Aryaka

   Traceroute
   ICMP though PAT {I think FW will identify each session based on Identification field}
   Bandwidth vs throughput
   DPD
   FW down, how long VPN will stay up
   Traceroute
   AnyCache Route
   Need for NAT-T
   Congestion Control
   Active vs Passive FTP
   WAN Optimization
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