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Chapter 8 Typo: broadcast should be multicast #309

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Chapter 8 Typo: broadcast should be multicast #309

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Expand Up @@ -339,7 +339,7 @@ However, sadly, there's a fatal flaw in my idea of using {{ICMP_ECHO}} to discov

+++ Cooperative Discovery Using UDP Broadcasts

Multicast tends to be seen as more modern and "better" than broadcast. In IPv6, broadcast doesn't work at all: you must always use broadcast. Nonetheless, all IPv4 local network discovery protocols end up using UDP broadcast anyhow. The reasons: broadcast and multicast end up working much the same, except broadcast is simpler and less risky. Multicast is seen by network admins as kind of dangerous, as it can leak over network segments.
Multicast tends to be seen as more modern and "better" than broadcast. In IPv6, broadcast doesn't work at all: you must always use multicast. Nonetheless, all IPv4 local network discovery protocols end up using UDP broadcast anyhow. The reasons: broadcast and multicast end up working much the same, except broadcast is simpler and less risky. Multicast is seen by network admins as kind of dangerous, as it can leak over network segments.

If you've never used UDP, you'll discover it's quite a nice protocol. In some ways, it reminds us of 0MQ, sending whole messages to peers using a two different patterns: one-to-one, and one-to-many. The main problems with UDP are that (a) the POSIX socket API was designed for universal flexibility, not simplicity, (b) UDP messages are limited for practical purposes to about 512 bytes, and (c) when you start to use UDP for real data, you find that a lot of messages get dropped, especially as infrastructure tends to favor TCP over UDP.

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