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What's the IP address of my Raspberry Pi?

This used to be a frequently-asked question by newcomers - at least those who were operating in "headless mode". They had bought a Raspberry Pi, burned a Raspbian image to its microSD card, and applied power. So far so good, but they would like to connect to the Raspberry Pi at some point!

However initiating an SSH connection also required one missing piece of information: What's the IP address of my new RPi?

ssh pi@?????????  # WHAT'S THE IP ADDRESS?

I attempted to explain what's responsible for this issue in this rumination piece on arp, aka the Address Resolution Protocol. And I offered a potentially unpopular opinion there: The RPi organization should fix this; at least mitigate the issue. Perhaps the solution would involve the boot folder, since it's a FAT partition, and easily readable and writeable by all OS?

But perhaps you shouldn't care about the IP address?

Since the introduction of mDNS or zeroconf networking and avahi in RPi, this has mostly become a "non-problem" - at least if they're using macOS or Linux hosts to initiate the SSH connection to the RPi. Many macOS users will have Bonjour "out of the box", and Linux users will also have avahi - if it's installed. Even some Windows users may benefit from zeroconf if they've installed Bonjour, or perhaps iTunes. But then some Windows users don't want it. Perhaps the simplest way to learn if you're a beneficiary of zeroconf is simply to try this command:

ssh [email protected]

This often works, but only if four conditions are satisfied:

  1. pi is the default user on RPi,
  2. raspberrypi is the default hostname,
  3. avahi is installed on RPi, and started automatically at boot (by systemd these days), and
  4. the host intitating the SSH connection has a zeroconf daemon installed; typically for macos & Linux.

Use of the .local suffix for mDNS/zeroconf clients has been a bit chaotic, in part because of Microsoft's inconsistent and conflicting support advice to their user base. However, as zeroconf has "picked up steam", this seems to have become less problematic.

The .local suffix is worth expending a few sentences. First, there are some who seem to fear that the .local suffix is a security risk?! I don't feel this is a valid concern; .local is a Special Use Domain Name used for Multicast DNS iaw Section 3 of RFC 6762. However, Microsoft offers conflicting advice re the use of .local, so Windows users should perhaps pay attention to Microsoft's inconsistent recommendations.

In Raspberry Pi the use of the .local suffix is included in the default configuration for avahi, under /etc/avahi-daemon.conf. See man avahi-daemon.conf for guidance and options, and note the default value: domain-name=.local. Also note that it's typically not necessary to edit /etc/avahi-daemon.conf as the daemon reads /etc/hostname, and (in Debian at least) the /etc/hosts file includes an entry for 127.0.1.1 which also typically reflects the hostname.

IP address discovery

All that said, here's an approach I outlined in response to a question on StackExchange some time ago. Here's the "recipe", and some inline code that I copied from here. Finally, if you're interested, here's some background on why this question gets asked so frequently.

Try this first:

arp -a | grep -E --ignore-case 'b8:27:eb|dc:a6:32'

The two hex strings (b8:27:eb|dc:a6:32) in this command reflect the two OUI values used by "The Foundation" for production of all RPi devices - through RPi ver 4B as of this writing. If your RPi isn't in your arp cache this command won't yield anything useful. If that's the case, then create the following file in your favorite editor on your Mac, and save/write it as pingpong.sh:

#!/bin/sh

: ${1?"Usage: $0 ip subnet to scan. eg '192.168.1.'"}

subnet=$1
for addr in `seq 0 1 255 `; do
( ping -c 3 -t 5 $subnet$addr > /dev/null ) &
done
arp -a | grep -E --ignore-case 'b8:27:eb|dc:a6:32'

make it executable:

chmod 755 pingpong.sh

and then execute it (use your network address here, not necessarily 192.168.1.):

bash pingpong.sh 192.168.1.

-- or --

./pingpong.sh 192.168.1.

Your output may look like this: This output reflects my network; it has 2 RPis connected, and one of them is a 3B+ with WiFi enabled and the Ethernet port connected to a switch (or router):

? (192.168.1.19) at b8:27:eb:3a:b9:78 on en0 ifscope [ethernet]
? (192.168.1.27) at b8:27:eb:cd:2f:ff on en0 ifscope [ethernet]
? (192.168.1.28) at b8:27:eb:cd:2f:ff on en0 ifscope [ethernet]

This case is interesting: My "old" RPi is connected to a Ethernet switch with IP address is 192.168.1.19. My "new" RPi 3B+ is connected to the same Ethernet switch, and also has its built-in WiFi enabled. It seems wrong that both the Ethernet and the WiFi adapters use the same MAC address! No idea what's going on here, but apparently this is a "feature" of Raspbian since I haven't changed it!

That's it; knowing the IP address you can now initiate an SSH connection to your RPi. Final note: This script was executed on my MacBook, so YMMV on a different platform.