Question about network (Are these results of arp a normal?) I have a question regarding my network; can anyone tell me if this is a problem or not?
When giving the command arp -a in the terminal, I see all my connected devices, but there are a bunch of IP addresses that have a different IP numbers and I don't recognize them.
See my log:
Mac-mini-2018-van-Richard:~ richard$ arp -a
? (192.168.1.1) at 90:72:40:9:37:e on en0 ifscope [ethernet]
? (192.168.1.2) at b8:ec:a3:21:d0:37 on en0 ifscope [ethernet]
? (192.168.1.3) at 74:a:bc:10:4b:7c on en0 ifscope [ethernet]
? (192.168.1.4) at d8:49:2f:23:79:13 on en0 ifscope [ethernet]
? (192.168.1.5) at 84:c0:ef:c0:2b:4e on en0 ifscope [ethernet]
? (192.168.1.6) at bc:99:11:94:b4:98 on en0 ifscope [ethernet]
? (192.168.1.7) at 18:b4:30:d2:a4:f1 on en0 ifscope [ethernet]
? (192.168.1.9) at e0:33:8e:d1:94:34 on en0 ifscope [ethernet]
? (192.168.1.10) at 0:6:78:32:14:25 on en0 ifscope [ethernet]
? (192.168.1.12) at 48:d7:5:ef:41:c2 on en0 ifscope [ethernet]
? (192.168.1.23) at 5c:f4:ab:63:e3:30 on en0 ifscope [ethernet]
? (192.168.1.27) at f8:46:1c:a0:58:19 on en0 ifscope [ethernet]
? (192.168.1.29) at 40:cb:c0:ac:3d:fb on en0 ifscope [ethernet]
? (192.168.1.44) at f0:18:98:e8:6d:6 on en0 ifscope permanent [ethernet]
? (192.168.1.52) at dc:a6:32:6f:ad:72 on en0 ifscope [ethernet]
? (192.168.1.55) at 0:6:78:20:a:9f on en0 ifscope [ethernet]
? (192.168.1.56) at 50:de:6:9a:7f:19 on en0 ifscope [ethernet]
? (192.168.1.59) at 3c:6a:9d:14:38:6d on en0 ifscope [ethernet]
? (192.168.1.255) at ff:ff:ff:ff:ff:ff on en0 ifscope [ethernet]
all-systems.mcast.net (224.0.0.1) at 1:0:5e:0:0:1 on en0 ifscope permanent [ethernet]
? (224.0.0.251) at 1:0:5e:0:0:fb on en0 ifscope permanent [ethernet]
? (225.11.89.110) at 1:0:5e:b:59:6e on en0 ifscope permanent [ethernet]
? (225.255.255.255) at 1:0:5e:7f:ff:ff on en0 ifscope permanent [ethernet]
? (227.72.38.171) at 1:0:5e:48:26:ab on en0 ifscope permanent [ethernet]
? (230.128.242.42) at 1:0:5e:0:f2:2a on en0 ifscope permanent [ethernet]
? (230.226.118.14) at 1:0:5e:62:76:e on en0 ifscope permanent [ethernet]
? (232.140.250.183) at 1:0:5e:c:fa:b7 on en0 ifscope permanent [ethernet]
? (234.51.79.222) at 1:0:5e:33:4f:de on en0 ifscope permanent [ethernet]
? (236.85.84.112) at 1:0:5e:55:54:70 on en0 ifscope permanent [ethernet]
? (236.202.5.112) at 1:0:5e:4a:5:70 on en0 ifscope permanent [ethernet]
? (237.30.215.60) at 1:0:5e:1e:d7:3c on en0 ifscope permanent [ethernet]
? (239.140.109.112) at 1:0:5e:c:6d:70 on en0 ifscope permanent [ethernet]
? (239.255.255.250) at 1:0:5e:7f:ff:fa on en0 ifscope permanent [ethernet]
? (239.255.255.250) at 1:0:5e:7f:ff:fa on en1 ifscope permanent [ethernet]
broadcasthost (255.255.255.255) at ff:ff:ff:ff:ff:ff on en0 ifscope [ethernet]

Can anyone tell my if the IP numbers starting with 2 are okay or can they be harmful?
Those IP’s are fine.

the 225 address are usually broadcast addresses (Class E)
Three are Class D IPs and is reserved for Multicast.  They're not even valid IPs for network nodes.

They are perfectly safe and pose no threat.