Troubleshoot Remote Network, Name Resolution & Ports

What counts as one hop when a packet is forwarded to a remote network?

Each router in the path to the network

What can the path taken by a packet be used to diagnose?

Routing issues

What is the tracert command used to do?

Trace the path a packet of information takes to get to its target

What can tracert take as an argument?

An IP address or FQDN

What happens if the host cannot be located with tracert?

The command will eventually timeout, but it will return every router that was attempted

What does tracert output show?

The number of hops, the ingress interface of the router or host, and the time taken to respond to each probe in milliseconds

What does an asterisk in tracert output mean?

No acknowledgment was received within the timeout period

What does pathping do as an alternative to tracert?

Performs a trace and then pings each hop router a given number of times for a given period

What does pathping determine and measure more accurately?

The round-trip time $RTT$ and link latency

What additional information does pathping show?

Packet loss at each hop

What should you check first if there is a routing issue?

That the local router's Internet connection status is OK

If the router is connected, what should you verify next?

That there are no wider network issues or DNS problems using the ISP's service status page or support helpline

What should you try if there are no ISP-wide issues?

Restarting the router

What does FQDN stand for?

Fully Qualified Domain Name

What three higher-layer areas should you suspect if basic connectivity seems fine?

Security, name resolution, and application/OS

What higher-layer problem could block the connection or involve misconfigured proxy settings?

Security

What higher-layer problem exists if you can connect by IP address but not by name?

Name resolution

What higher-layer problem might exist if the server can be contacted but a specific service is unavailable?

The service process might have crashed

Why should you establish the scope of the problem when troubleshooting unavailable network resources?

To determine whether the problem lies with the first client or with the server, print device, or network infrastructure

If you can connect to a service using a different host, where should the problem lie?

With the first client

If other hosts cannot connect, where does the problem lie?

With the application server or print device or with network infrastructure between the clients and the server

What does DNS do?

Converts human-readable names into computer-readable IP addresses

What does it indicate if pinging a host name fails but pinging its IP address works?

A name resolution issue

Which command can you run to check DNS settings on the network adapter?

ipconfig /all

Which command clears local DNS records?

ipconfig /flushdns

What command can you use to test the DNS server connection?

nslookup

What does nslookup query?

DNS servers for names and IP addresses

What can Host be in nslookup?

A host name/FQDN or an IP address

What is Server in nslookup?

The DNS server to query

What happens if the Server argument is omitted in nslookup?

The default DNS server is used

What does -Option specify in nslookup?

An nslookup sub-command

What is a typical use of an nslookup sub-command?

To query a particular DNS record type

What can comparing results from a different name server help highlight?

Configuration problems

What can you try if the DNS server is not responding?

Use a different DNS server address to verify if the issue is with the DNS server

What is the netstat command used to investigate on the local host?

Open ports and connections

How can netstat help in troubleshooting file sharing or email issues on a server?

Verify whether file sharing or email ports are open on a server and whether other clients are connecting to them

What does netstat list when used without switches?

Active and listening TCP ports

What is an active port in netstat?

A port connected to a foreign address

What is a listening port in netstat?

A port waiting for a connection

What does netstat -a include?

UDP ports in the listening state

What does netstat -b show?

The process that has opened the port

What does netstat -o show instead of the process name?

The process ID $PID$

Which netstat switches require an administrative command prompt?

-b and -o

What does netstat -n display?

Ports and addresses in numerical format

Why does netstat -n speed up each query?

Because it skips name resolution

What do netstat -e and netstat -s report?

Ethernet statistics and protocol statistics, respectively

What common Windows file sharing and printer sharing port might netstat help verify?

SMB on tcp/445

What common email receive port might netstat help verify for IMAP4?

tcp/143

What common email receive port might netstat help verify for POP3?

tcp/110

What common email transfer port might netstat help verify for SMTP?

tcp/25