QETHARP(8)

💅 QETHARP(8) — like, the ARP queen of s390, bestie

okay so real talk: this is qetharp(8) from the System Manager's Manual and it is literally the main character of ARP cache management on your box. grab a snack, we're getting into it 🍓

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✨ NAME ✨

qetharp — querying and modifying ARP data. that's it, that's the vibe 💅

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🦋 SYNOPSIS 🦋

qetharp [-hv]
        [-[c|n][6]q interface]
        [-p interface]
        [-a interface -i IP_address -m MAC_address]
        [-d interface -i IP_address]

look at that flag choreography. iconic. no notes. 👑

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🌸 DESCRIPTION 🌸

so qetharp queries ARP data — think MAC and IP addresses — out of an OSA hardware ARP cache or a HiperSockets ARP cache. and for OSA hardware specifically? it can also modify the cache. she doesn't just read, she edits. 📝

two things you need to know before you go feral with it:

• The command applies only to devices in layer3 mode. not layer2. layer3. periodt.
• It supports IPv6 for HiperSockets only. so don't come for OSA with your IPv6 business, it's not that girl.

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💖 OPTIONS 💖

• -q or --query interface — shows the ARP information about the specified network interface. depending on which device that interface got assigned to, this info comes either from an OSA feature's ARP cache or from a HiperSockets ARP cache. the default output shows symbolic host names, and it only throws in a numerical address for host names that just cannot be resolved (tragic, but fair). want numbers instead of names? use -n. and heads up: by default qetharp omits IPv6 related info — use -6 to include IPv6 information for HiperSockets.
• -n or --numeric — shows numerical addresses instead of trying to resolve addresses to symbolic host names. ngl this one's a package deal: it can only be used with the -q option. 🫶
• -c or --compact — limits the output to numerical addresses only. also a package deal — this option can only be used with the -q option.
• -6 or --ipv6 — includes IPv6 information for HiperSockets. for real HiperSockets, it shows the IPv6 addresses; for guest LAN HiperSockets, it shows the IPv6 to MAC address mappings. and yeah, you guessed it — this option can only be used with the -q option. ✨
• -p or --purge interface — flushes the ARP cache of the OSA. the cache holds dynamic ARP entries, which the OSA adapter creates through ARP queries. after flushing, the OSA adapter goes right back to creating new dynamic entries (she's resilient like that 💀). this option only works with OSA devices.
• -a or --add interface — adds a static ARP entry to the OSA adapter card. this option requires an IP address and a MAC address (that's the -i and -m options, bestie).
• -d or --delete interface — deletes a static ARP entry from the OSA adapter card. this command requires an IP address (the -i option).
• -i or --ip IP_address — specifies an IP address to be added to or removed from the OSA adapter card.
• -m or --mac MAC_address — specifies a MAC address to be added to the OSA adapter card. 🎀
• -v or --version — shows version information.
• -h or --help — shows usage information for qetharp.

ok quick PSA: -n, -c, and -6 are all -q-only girlies. don't try to run them solo, it's not gonna slay. 🙈

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⭐ RETURN CODES ⭐

qetharp writes the response to stdout and any error message to stderr. the command completes with one of these:

• 0 — The qetharp command ran successfully. we love a win. 🎉
• 1 — An error occurred. 💀

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🌈 EXAMPLE 🌈

• qetharp -q eth0 — shows all ARP entries of OSA.
• qetharp -nq eth0 — shows all ARP entries of OSA without resolving host names.
• qetharp -6q hsi0 — shows all ARP entries of the HiperSockets interface including IPv6 entries.
• qetharp -n6q hsi0 — shows all ARP entries of the HiperSockets interface including IPv6 entries without resolving host names.
• qetharp -p eth0 — flushes the OSA ARP cache for eth0.
• qetharp -a eth0 -i 1.2.3.4 -m aa:bb:cc:dd:ee:ff — adds a static ARP entry for the IP address 1.2.3.4 to the OSA ARP cache, using a MAC address of aa:bb:cc:dd:ee:ff
• qetharp -d eth0 -i 1.2.3.4 — deletes the static ARP entry for the IP address 1.2.3.4 from the OSA ARP cache.

qetharp -q eth0
qetharp -nq eth0
qetharp -6q hsi0
qetharp -n6q hsi0
qetharp -p eth0
qetharp -a eth0 -i 1.2.3.4 -m aa:bb:cc:dd:ee:ff
qetharp -d eth0 -i 1.2.3.4

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👑 AUTHOR 👑

This man-page was written by Frank Pavlic <pavlic@de.ibm.com> — shoutout to Frank, fr fr, absolute legend for this one 🫶

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and that's the page!! 🧚 this little beauty ships with s390-tools, dated Nov 2011 — yes she's vintage, and yes she still ate. bye bestie, go flush some caches responsibly 💜🌸