Ports, protocols, and the addresses to recognise
Objective 109.1 is the fundamentals under everything else in topic 109: the file that maps service names to port numbers, the difference between a TCP listener and a UDP socket, the port numbers the exam expects on sight, protocol numbers, and the IPv6 addresses that exist on every interface whether or not anyone configured them.
102: Networking Fundamentals Guide 29 of 33 Beginner
- PlatformsUbuntu 26.04 LTS + AlmaLinux 10.2
- TimeAbout 20 min
- RPM packagingrpm 4.19.1.1, dnf 4.20.0
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| LPIC1-A01 | 192.168.0.76 | Ubuntu 26.04 LTS | Debian-family host - dpkg and apt, which objective 102.4 names | 2 Core | 4 GB | 50 GB |
| LPIC1-B01 | 192.168.0.77 | AlmaLinux 10.2 | RPM-family host - rpm and dnf, which objective 102.5 names | 2 Core | 4 GB | 50 GB |
This guide includes
Use this when reading a firewall rule, a listener list or a packet capture and the numbers need to mean something without a lookup. This matters because a port number on its own is ambiguous - 514 is one service over TCP and a different one over UDP - and because the file those names come from is thirty times larger on one family than the other.
- reading
/etc/servicesand querying it the way a program does, withgetent - separating TCP listeners from UDP sockets, and seeing why one has no LISTEN state
- recognising the port numbers the exam uses, and finding the two the lookup cannot answer
- reading protocol numbers from
/etc/protocols, which are not port numbers - finding the link-local and loopback IPv6 addresses every machine already has
Before you start
- addresses-routes-and-what-the-mask-decides
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The file that turns a name into a number
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TCP and UDP are different listeners on the same machine
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The numbers the exam expects you to recognise
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IPv6, which the objective names and most labs ignore
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The same questions on the RPM family
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Nothing to put back