This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.
What this hour is for
tcpdump copies packets from an interface. The command builder and the BPF builder draft text. You choose the interface, the host, and a count. A capture without a count runs until the disk fills.
Use a host you administer. A documentation address in a sample is replaced before you run anything. Do not capture a trunk of users. Do not write a filter to extract passwords.
Read the interface name twice. The wrong interface is someone else's traffic or a useless file. Stop the command when the count hits or the question is answered.
A file you save is a secret-bearing file until you have looked. Delete it with the ticket.
The change you can finish
Apply nothing during the writing of the note. When the lab window opens, it is one change on the device named in the ticket. Read the draft, then the device, then decide.
Rollback is the file or the revision you saved first. You do not invent a rollback after the only copy is gone.
- Name the interface and the host you run.
- Draft a command with a count.
- Read the filter.
- Replace sample addresses.
- Run it only in the lab window, then stop.
- Delete the file when the ticket closes.
Mistakes that outlive the command
tcpdump Cheat Sheet goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- No count.
- The wrong interface.
- A password filter.
- A network you do not administer.
- The file kept with no owner.
Decisions to write down
One decision for tcpdump Cheat Sheet: The interface is yours. The count is set. The filter is readable. Sample addresses are gone. And the file has a deletion plan.
Checks before you call it done
Confirm this before you call the change done: The command is in the ticket with the count. The interface was confirmed. No password filter is present. The command is stopped. And the file owner is named. If one of those fails, stop.
A count and a host you administer.
Stop when the count finishes.Before you leave the device
tcpdump Cheat Sheet ends when the hostname on the device matches the hostname in the ticket. If it does not, you are on the wrong box. Stop. A command that succeeded on the wrong box is not progress.
The draft stays a draft until a person has read the names in it. A generator does not log into the device and does not know which interface is the uplink. You delete a line that names a device, a zone, or a prefix you did not write down.
0.0.0.0/0 is not kept because a sample included it. A source you can say is the source you keep. 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. They belong in the note. They are not prefixes you type onto a production device because they appeared in a draft.
prompt-for-this is a reminder that a secret is missing. It is not a password, a key, a community string, or a pre-shared key you save in the ticket or in git. The real secret stays in the store.
One change is the window. A VLAN and a routing protocol and a VPN do not share it. If two things move and the result is wrong, you will not know which one did it. The next feature waits for its own page.
If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied config produces a device nobody can rebuild. Restore the copy you took first.
A second person reads the device name and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the device alone.
This page is a planning guide. It is not a vendor manual, not an official standard, and not a permission to touch a network you do not administer. The pillar guide owns the wider design. This page owns one lab proof.
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