ITPro.TV: CompTIA Security+ (SY0-601) & TryHackMe: Jr. Penetration Tester

author: Nathan Acks
date: 2022-03-29

ITPro.TV: CompTIA Security+ (SY0-601)

Network Security - Segmentation

A hub is a Layer 1 device - it’s just a multi-port repeater.

VLAN logic is applied to Layer 2 - they’re basically a way of dividing up the ports on a switch (this makes me feel better about how I’ve been using them at work…). Data is routed between VLANs by the router (i.e., at Layer 3).

While the canonical DMZ has a firewall on both the north and south side, in practice only a single firewall is generally used. Other terms for a DMZ:

Think of an extranet as a purposeful network of intranets. Normally this is achieved via VPN connections.

North/South traffic can be thought of as traffic that crosses a security boundary (and thus should be touched by a router/firewall), while east/west traffic is traffic within the security perimeter.

Network Security - VPNs

Broad types of VPNs:

VPN tunneling protocols:

VPN concentrators are falling by the wayside, as this functionality is typically built into next-generation firewalls.

Network Security - Proxies And Load Balancing

These days, proxies are mostly about controlling access to resources. They are particularly important for logging purposes.

Forward proxies handle outbound traffic to external networks.

Reverse proxies handle inbound traffic from external networks.

Load balancers help distribute load, and in doing so help ensure availability. Types of load balancers:

Servers behind a load balancer can also be set up in active/active or active/passive fashion. Additionally, active servers are typically accessed (“scheduled”) in one of two ways:

Both of these access methods can be weighted in various ways.

Network Security - Port Security

This is about the security of physical switch ports.

Spanning Tree Protocol (STP) is used to protect against looping and packet storms. Basically, in STP switches will communicate to elect a “root node”, and then build a tree of reachable switches from that node. Ports are dynamically disabled as necessary when loops are detected.

STP operates using BPDU (Bridge Protocol Data Unit) frames. To stop malicious BPDU frames, BPDU guard marks certain ports as privileged (those connected to other, legitimate, switches), and rejects BPDU frames on all other ports.

Another security measure implemented on switches (though it’s not really a Layer 2 security protocol) is DHCP snooping. This is similar to BPDU guard, in that a privilege port is identified where the legitimate DHCP server is connected, and makes sure that server packets to and from unauthorized ports are blocked.

Switches can also do MAC address filtering (like wireless networks), and even restrict particular MAC addresses to particular ports.

Some switches can also mirror ports (sometimes also called “port spanning”) for monitoring purposes.

Network Security - Firewalls

Stateless firewall = Packet filtering firewall (source, destination, port)

Stateful firewall = Dynamic packet filtering firewall (monitors connection requests)

Stateful firewalls keep track of connection state, and can block SYN flood attacks, etc.

Next-gen firewalls can deal with more OSI layers than just 3 - all the way up to the application layer.

Network Security - NIDS And NIPS

NIDS (Network Intrusion Detection Systems) and NIPS (Network Intrusion Prevention Systems) are generally built into next-gen firewalls.

Detection methods:

TryHackMe: Jr. Penetration Tester

Passive vs. Active Recon

Passive recon concerns information we can gather without interacting with our target. This is generally publicly available information, such as DNS records, social media posts, etc.

Active recon involved interacting with the target in some way. Connecting to systems, browsing their website, physical penetration of their facilities, etc.


WHOIS responses include name server information (in the aptly-named “Name Server” field(s)).

nslookup and dig

nslookup = Name Server Look Up

# nslookup command syntax; only $DOMAIN is required

# Examples
nslookup -type=A
nslookup -type=MX

dig = Domain Information Groper

# dig command syntax; only $DOMAIN is required

# Examples
dig @ A
dig @
dig    MX


DNSdumpster is basically a search engine for domain data - type in a root domain, and get back (many of) its subdomains and other information. (In my testing DNSdumpster doesn’t always enumerate every subdomain, though it certainly does a better job than guessing.)