Wireless networks have names and thus identify themselves

July 21, 2019

Recently something occurred to me that sounds obvious when I phrase it this way, which is that wireless networks have names. Wireless networks intrinsically identify themselves through their SSID. This is unlike wired networks, which mostly have no reliable identifier (one exception is wired networks using IEEE 802.1X authentication, since clients need to know what they're authenticating to).

This matters because there are a number of situations where programs might want to know what network they're on, so they can treat different networks differently. As a hypothetical example, browsers might want to apply different security policies to different networks. With wireless networking, the browser can at least theoretically know what network it's on; with wired networking, probably it can't (not reliably, at any rate).

(Another case where you might want to behave differently depending on what network you're connected to is DNS over HTTPS. On some networks, not only can you trust the DNS server you've gotten to be not malicious, but you know you need to use it to resolve names properly. On random others, you may definitely know you want to bypass their DNS server in favour of a more trusted DoH server.)

PS: I believe that Windows somewhat attempts to identify 'what network are we on' even on a wired connection, presumably based on various characteristics of the network it gets from DHCP information and other sources (this is apparently called 'network locations'). My experience with this is that it's annoying because it keeps thinking that my virtualized Windows system is moving from network to network even though it isn't. This makes a handy demonstration of the hazards of trying to do this for wired networks, namely that you're relying on heuristics and they can misfire in both directions.

Written on 21 July 2019.
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Last modified: Sun Jul 21 00:38:08 2019
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