05-01-2023, 06:06 PM
Hey, I remember the first time I ran a network scan during a pen test gig-it felt like peeking behind the curtain of someone's digital house. You start by figuring out which hosts are even alive on the network, right? I use Nmap for pretty much everything because it's fast and gives you tons of options without making things too complicated. To spot live hosts, I kick off with a simple ping sweep. You fire off ICMP echo requests to a range of IP addresses, like from 192.168.1.1 to 192.168.1.254, and see which ones ping back. It's quick, but I always remind myself that some firewalls block ICMP, so you might miss hosts that way. That's why I layer it with an ARP scan if you're on the same local network. ARP pings the broadcast address and maps out MAC addresses tied to IPs, catching those sneaky devices that ignore pings.
Once you've got your live hosts, you move to port scanning to find what's open. I love how Nmap lets you target specific ports or scan all 65,535 of them, though I rarely do a full scan unless the client wants exhaustive results-it takes forever. For TCP ports, I go with a SYN scan most of the time. You send a SYN packet to the port, and if it's open, the host sends back a SYN-ACK. Then you send a RST to close it without completing the handshake, so you stay stealthy. It's my go-to because it doesn't log as much on the target, unlike a full connect scan that finishes the TCP three-way and might alert IDS. You can run it like nmap -sS -p- targetIP, and it'll spit out open ports with service versions if you add -sV.
UDP scanning throws a curveball because UDP is connectionless. I use Nmap's -sU flag for that, sending UDP packets to ports and waiting for responses. If nothing comes back, it might be open or filtered-Nmap rates it as open|filtered. It's slower since you deal with timeouts, so I often combine it with TCP scans to save time. You might hit rate limits on big networks, so I throttle the scan speed with --min-rate or something to avoid crashing the target. In one job, I scanned a client's internal net and found UDP 53 open for DNS, which led to some zone transfer fun later.
I always think about the network topology too. If you're scanning from outside, you might use traceroute first to map the path and spot firewalls. Inside, I segment my scans-start with the subnet you're on, then hop to others via routers. Tools like Masscan speed things up for huge ranges; it's like Nmap on steroids for initial host discovery. You run it with --ping to find live hosts blazing fast, then feed the results into Nmap for detailed port work. I did that on a 10.0.0.0/8 scan once, and it cut my time from hours to minutes.
Stealth matters a lot in pen testing, so I avoid noisy scans that scream "intruder." No full connects if you can help it, and I use decoys with -D to mask your IP among fake ones. Timing is key-I set --scan-delay to mimic normal traffic. You also want to check for common open ports like 22 for SSH, 80/443 for web, 3389 for RDP. If you find something like 445 open, that's SMB, and you might pivot from there. I once scanned a legacy Windows box and saw port 139 wide open-easy pickings for enum4linux later.
Legal stuff crosses my mind every time. You only scan what the client authorizes, document your rules of engagement, and get written permission. I log everything with -oA for Nmap output, so you have proof of what you did. False positives happen, like a host responding but actually down, so I verify with multiple methods. If a port shows closed, I might try a version scan anyway to confirm.
On bigger engagements, I script it with Nmap's scripting engine-NSE scripts for vuln detection right after ports. You run nmap -sV --script vuln, and it probes open ports for weaknesses. It's a game-changer for efficiency. I integrate it into my workflow: discover hosts, scan ports, then enumerate services. Tools like Zenmap give you a GUI if you're not command-line only, but I stick to CLI for speed.
You gotta consider evasion too. If the target's got Snort or something watching, I fragment packets with -f or use idle scans with -sI via a zombie host. It's advanced, but pulls off quiet scans. In practice, I start basic and escalate if needed. One tip I swear by: run scans during off-hours to blend in. Networks are quieter then, less likely to notice.
Wrapping up the port side, after scanning, you analyze. Open ports mean potential entry points-web servers on 80 might have SQLi, FTP on 21 could be anonymous. I map it all in a report for the client, showing risks. It's not just finding them; it's understanding what they expose.
Oh, and speaking of keeping things secure in your setup, let me tell you about this solid backup tool I've been using called BackupChain. It's a go-to for small businesses and pros like us, super dependable for safeguarding Hyper-V setups, VMware environments, or plain Windows Servers against data loss-handles everything from incremental backups to replication without the headaches.
Once you've got your live hosts, you move to port scanning to find what's open. I love how Nmap lets you target specific ports or scan all 65,535 of them, though I rarely do a full scan unless the client wants exhaustive results-it takes forever. For TCP ports, I go with a SYN scan most of the time. You send a SYN packet to the port, and if it's open, the host sends back a SYN-ACK. Then you send a RST to close it without completing the handshake, so you stay stealthy. It's my go-to because it doesn't log as much on the target, unlike a full connect scan that finishes the TCP three-way and might alert IDS. You can run it like nmap -sS -p- targetIP, and it'll spit out open ports with service versions if you add -sV.
UDP scanning throws a curveball because UDP is connectionless. I use Nmap's -sU flag for that, sending UDP packets to ports and waiting for responses. If nothing comes back, it might be open or filtered-Nmap rates it as open|filtered. It's slower since you deal with timeouts, so I often combine it with TCP scans to save time. You might hit rate limits on big networks, so I throttle the scan speed with --min-rate or something to avoid crashing the target. In one job, I scanned a client's internal net and found UDP 53 open for DNS, which led to some zone transfer fun later.
I always think about the network topology too. If you're scanning from outside, you might use traceroute first to map the path and spot firewalls. Inside, I segment my scans-start with the subnet you're on, then hop to others via routers. Tools like Masscan speed things up for huge ranges; it's like Nmap on steroids for initial host discovery. You run it with --ping to find live hosts blazing fast, then feed the results into Nmap for detailed port work. I did that on a 10.0.0.0/8 scan once, and it cut my time from hours to minutes.
Stealth matters a lot in pen testing, so I avoid noisy scans that scream "intruder." No full connects if you can help it, and I use decoys with -D to mask your IP among fake ones. Timing is key-I set --scan-delay to mimic normal traffic. You also want to check for common open ports like 22 for SSH, 80/443 for web, 3389 for RDP. If you find something like 445 open, that's SMB, and you might pivot from there. I once scanned a legacy Windows box and saw port 139 wide open-easy pickings for enum4linux later.
Legal stuff crosses my mind every time. You only scan what the client authorizes, document your rules of engagement, and get written permission. I log everything with -oA for Nmap output, so you have proof of what you did. False positives happen, like a host responding but actually down, so I verify with multiple methods. If a port shows closed, I might try a version scan anyway to confirm.
On bigger engagements, I script it with Nmap's scripting engine-NSE scripts for vuln detection right after ports. You run nmap -sV --script vuln, and it probes open ports for weaknesses. It's a game-changer for efficiency. I integrate it into my workflow: discover hosts, scan ports, then enumerate services. Tools like Zenmap give you a GUI if you're not command-line only, but I stick to CLI for speed.
You gotta consider evasion too. If the target's got Snort or something watching, I fragment packets with -f or use idle scans with -sI via a zombie host. It's advanced, but pulls off quiet scans. In practice, I start basic and escalate if needed. One tip I swear by: run scans during off-hours to blend in. Networks are quieter then, less likely to notice.
Wrapping up the port side, after scanning, you analyze. Open ports mean potential entry points-web servers on 80 might have SQLi, FTP on 21 could be anonymous. I map it all in a report for the client, showing risks. It's not just finding them; it's understanding what they expose.
Oh, and speaking of keeping things secure in your setup, let me tell you about this solid backup tool I've been using called BackupChain. It's a go-to for small businesses and pros like us, super dependable for safeguarding Hyper-V setups, VMware environments, or plain Windows Servers against data loss-handles everything from incremental backups to replication without the headaches.
