Complete some missing infos

content/en/post/gamification-of-a-advanced-linux-sysadmin-course/index.md

@@ -188,6 +188,9 @@ They have the actual network topology at their disposal, as well as an IP addres
 
 ![Network topology provided for students to find their way around](topology.png)
 
+This step enables them to learn how to read a topology and practice with subnet masks.
+Some students will forget the mask when adding the IP to their interface, preventing them from contacting the server.
+
 The risk of such an exercise is that several students will take the same address and create IP conflicts, which would make the exercise far too difficult.
 To eliminate any risk of conflict, each student is given a protected address: this address is registered in the server's ARP table so that it can only communicate with its own workstation.
 
@@ -285,7 +288,7 @@ Whereas up to now all tokens had to be sent to a web server over an unencrypted
 So far, everything has seemed coherent, but this seemingly straightforward step - switching from HTTP to HTTPS - will reveal an unexpected problem, to say the least:
 
 ```
-42sh# curl
+42sh# curl https://172.23.200.1/challenge
 curl: (60) SSL certificate problem: certificate is not yet valid
 More details here: https://curl.haxx.se/docs/sslcerts.html
 ```
@@ -302,6 +305,12 @@ If the clock is too far off, the student receives a message reminding him that r
 
 To get past this stage, students are expected to discover clock synchronization tools, using the DMZ's NTP server.
 
+Once this stage has been validated, it's important to review the certificate stores with the students.
+Under normal circumstances, on a freshly installed machine, such a request should not have worked, as it is impossible to obtain a valid TLS certificate for a private IP.
+In this case, I had placed an additional authority in their system store, which I control.
+So I'm able to intercept any encrypted traffic their applications might emit.
+This is a particularly important point of awareness.
+
 
 ### Step 8: Domain name resolution
 
@@ -334,6 +343,7 @@ To ensure that all students without exception are confronted with this problem,
 The students are thus forced to find the server's true MAC among all the MACs responding to requests.
 They also discover the static entries in the ARP table.
 
+This step also opens the door to *ARP spoofing* and the dangers of unprotected wireless access points.
 
 ### Step 10: Traceroute
 
@@ -377,6 +387,11 @@ A virtual disk is created at system start-up, a file is created with a unique to
 This bonus is designed to show the experienced student how to use file recovery tools.
 
 
+### 4. Send an e-mail with the command line
+
+The aim of this bonus is to introduce students to the format of e-mails, making them aware that the sender is just a header and can be easily falsified.
+
+
 ## Variants
 
 I'm showing here a standard framework for the exercise I've designed. Depending on expected needs, it is possible to deviate from this scenario.