· Linux experience?
· Commands - (grep, pwd, ls, cd, tar, find, chmod)
Remember, Linux/Unix isn’t a necessary skill to get hired…maybe an S7/S8 should have some Linux experience, but others really don’t. I spend less than 2/3 minutes with Linux questions….
· Do you have any Linux experience?
· Yes, then what’s some common commands you use? ls, grep, cd, pwd, ps, top…
· No, then move on to next subject…
· Microsoft equivalent commands – ipconfig=ifconfig; nslookup=dig
Unix questions
- how to remove all files in a directory
Answer:
Rm -f
Vi (how do I exit out of vi)
Answer:
Press escape, press "I" to shift between modes, then press :wq!
How to run a task in the background
Answer:
Put & at the end of the command
How to view running tasks
Ps aux
Top
Runtime levels
Init 0 (shuts down the computer)
Init 1 (boots computer into single user mode)
Init 5 (reboots into normal mode)
Scenario:
You are having trouble with your Apache webserver and you have been asked to restart the service. How would you do this?
What I am looking for:
Candidate should know that Apache webserver runs as httpd daemon. Technically they could answer with:
Httpd restart
But they should also know how to do it the long way. First you must identify the process ID of Apache
Ps aux | grep http*
From the screenshot above we see the process ID numbers for httpd (82561-82565)
To ki-l the process:
Ki-l 82561
Now let's say you try to ki-l the process but you don't have permission.
What should you do?
Answer:
Run the command with sudo
Sudo ki-l 82561
How do I copy files from one Unix server to another?
Answer:
Scp
What is the default shell installed on Unix/Linux
Answer: bash
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- What are the 7 layers of the OSI Model and give a description of each?
Physical, Data Link, Network, Transport, Session, Presentation, Application
- Which layer is responsible for establishing the session (duplex) between hosts?
L5 – Session
- Which layer handles SSL/TLS encryption for HTTP?
L6 – Presentation
- What are the 2 types of ports on a Cisco Switch?
Access and Trunk
- How many steps does it take to open and close a TCP connection?
3 to open - SYN/SYNACK/ACK
3-4 to close - FIN/FINACK/ACK?
- What is an abnormal connection termination in a packet capture?
Reset (RST)
- What are MSS and MTU?
Maximum Segment Size - largest amount of data that can be sent per segment over TCP, minus the header.
Maximum Transmission Unit - largest packet that can be sent over the network.
1500 MTU
20 IP header
20 TCP header
1460 MSS
- How many bits are in an IP address and how many bytes makes up the MAC?
32 for the IPv4.
128 for IPv6.
6 bytes for the MAC.
48 bits in a MAC.
- What is the purpose of a trunk port?
To provide VLAN identification for frames between switches.
- What are the two types of trunked ports on a Cisco Switch?
ISL (Inter-switch Link) and 802.1q
- How does TCP differ from UDP? What are some advantages and disadvantages of each protocol?
TCP is connection oriented, UDP is connectionless. TCP has error checking and can reorder packets, but is slower than UDP. UDP is faster, but has no concept of retransmits for missed data.
- What is Cisco VTP and why should it be used?
VLAN Trunking Protocol, A method of managing VLANs between switches.
- What is Spanning Tree and what are the typical port states?
Spanning Tree Protocol (STP) is a Link Layer protocol that prevents loops.
Blocking, Listening, Learning, Forwarding, Disabled
- What is an advantage of RSTP over STP?
RSTP can update a port in 6 seconds vs. the 30+ for STP.
- What is Portfast and when should it NOT be used?
Allows a port into a forwarding state immediately when active. Shouldn’t be used for ports where bridges, switches, or STP devices are connected.
- What is Link Aggregation and when should it be used?
- 1ax, 802.3ad before 2008, describes using multiple network ports in parallel to increase the link speed greater than any single port, and to increase the redundancy for higher availability.
- Using LACP, is it possible to configure an EtherChannel across multiple switches for a single server?
No, a limitation of Link Aggregation is that all ports must be the same speed and reside on the same logical switch. VSS and Stacked switches can create a MEC (Multichassis Etherchannel)
- What are some packet capture tools that can be used on the client and server?
snoop, tcpdump, ethereal, wireshark, tshark, ssldump, netscout
- What is a SPAN port and how do you set it up?
Switched Port Analyzer, A method to send a copy of packets from one port to another monitoring port for inspection.
Command to setup SPAN port CATOS:
Console> (enable)set span 1/36,1/7 1/48
Console> show span
Console> set span disable
Command to setup SPAN port for IOS:
Switch>en
Switch#conf t
Switch(config)#monitor session 1 source interface fa0/1 both
Switch(config)#monitor session 1 destination interface fa0/2
Switch(config)#end
Switch# show monitor session 1 (To verify)
Switch# show monitor session 1 detail (Verify in detail)
Switch (config)#no monitor session 1 (To disable)
- Scenario based question, the NOC has noticed an HA pair of Load-balancers has failed over from the Primary to Secondary device, but 2 of the 400 VIPs are failing. All requests directly to the backend servers supporting those 2 VIPs are working. How would you troubleshoot this failure?
- Look for ping of IPs
- check ARP table on the switches
- Issue a clear ARP on the switches
- force ARP on the current primary device.