Why do you get a tiny browser pops up when you connect your iPhone to Guest network

>Apple has designed the ios devices in such a way that whenever you connect your iphone to a captive portal designed wifi network they bring it to your notice by popping up a tiny browser  that you have to authenticate to get on internet.

>How does this work on the background?

155.726863 192.168.242.85 -> 192.168.242.15 DNS Standard query A captive.apple.com
155.901921 192.168.242.15 -> 192.168.242.85 DNS Standard query response CNAME captive.apple.com.edgekey.net CNAME e7279.dsce9.akamaiedge.net A 104.72.84.134
155.929087 192.168.242.85 -> 104.72.84.134 TCP 65431 > http [SYN, ECN, CWR] Seq=0 Win=65535 Len=0 MSS=1416 WS=5 TSV=760100837 TSER=0 SACK_PERM=1
155.930144 104.72.84.134 -> 192.168.242.85 TCP http > 65431 [SYN, ACK] Seq=0 Ack=1 Win=5792 Len=0 MSS=1460 SACK_PERM=1 TSV=8650997 TSER=760100837 WS=0

>Once the devices gets a IP address the iphone tries to send traffic to captive.apple.com and if gets any reply the device knows that the user have already authenticated.

>If  the device not able to reach the captive.apple.com then it understands that there is a captive portal to authenticate  further.

>In this sample capture the device gets a response from 104.72.84.134 , he know that it does has internet access and CNA is not required.

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