Talk:Broadcast address

OR not AND

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In the page you state that

"Generally, the broadcast address is found by taking the logical bit complement of the subnet mask and then logically ANDing this with the IP address."

and then give the example:

"This can be found from the subnet mask (255.255.0.0) and the IP address (eg. 172.16.48.196 - the complement of the subnet mask is 0.0.255.255, and 172.16.48.196 && 0.0.255.255 = 172.16.255.255."

For that calculation the last operation schould be OR and not AND.

Please take note.

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Definition of broadcast address

Wouldn't it be simpler to say : "The broadcast address is an address which has all host-part bits set to 'one'" ?

Also, at least linux allows using a different broadcast address. Older linux disributions asked as part of the network setup for the broadcast address. Can someone clarify why those broadcast addresses were used/allowed ?

xerces8 --86.61.2.139 14:27, 11 June 2006 (UTC)

Setting the host identifier bits to 1 is now described as an alternative to bitwise arithmetic.

Does anyone have a citation for manual configuration of broadcast address? ~Kvng (talk) 16:24, 5 April 2020 (UTC)

Ummm...

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Am I missing something here? I thought the subnet mask of the 172.16.0.0 network was 255.240.0.0. That would mean that the broadcast address would be 172.31.255.255, surely? - Tbsdy lives (formerly Ta bu shi da yu) ^talk 10:19, 12 January 2009 (UTC)

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Legacy broadcast

A number of devices still treat the .0 address as a broadcast address (including, surprisingly, the Linux kernel). There should be some mention in the article of the history of this (which I'm not totally sure of, but IIRC both .255 and .0 were broadcast until a number of years ago, when .0 was deprecated - although it's still not recommended even today). 146.87.6.75 (talk) 14:50, 8 May 2009 (UTC)

Does anyone have a citation for this? ~Kvng (talk) 16:24, 5 April 2020 (UTC)

Not sure the following demonstrates what you meant. Quoting whats-the-difference-between-127-0-0-1-and-127-0-0-0#comment703601_575651. For me, the relevant part here is in the top lines:

True. 127.0.0.0 with mask 255.255.255.255 could theoretically also work. In praxispractice that is a very bad idea. since old software used to use the lowest address in a range as broadcast address. – Hennes Mar 30, 2013 at 11:29

176.12.184.6 (talk) 23:11, 31 December 2023 (UTC)

That's evidence that could motivate us to investigate further but since it is WP:UGC it is not something we can use as a citation. It also says old software so does not support the claim above that the behavior exists in Linux. ~Kvng (talk) 15:42, 4 January 2024 (UTC)

with UDP not TCP

Mustn't we mention in the definition that it only works with UDP not TCP ? — Preceding unsigned comment added by 91.240.81.106 (talk) 18:21, 2 September 2019 (UTC)

This is an internet layer feature and works for all transport layer protocols. ~Kvng (talk) 16:24, 5 April 2020 (UTC)

I think UDP and TCP should be mentioned *somewhere* in the definition, since most people have some idea what they are but don't know what a datagram is. Therefore, I've changed the definition from "A broadcast address is a network address at which all devices connected to a multiple-access communications network are enabled to receive datagrams" to "A broadcast address is a network address at which all devices connected to a multiple-access communications network are enabled to receive datagrams, which comprise UDP and TCP/IP packets, for instance." (new part added in bold). I think this is appropriate, but if someone has a better way of mentioning UDP and TCP/IP somewhere in the first paragraph, I'd be fine with that too. ERCaGuy (talk) 22:20, 5 April 2020 (UTC)

Introducing the example shown in the table

@Kvng: You've deleted my intro to the example table, but I feel very strongly this is an essential addition that really helps this page be more readable and easy to understand. The table takes some careful study, and my one sentence intro. makes that study 5x faster. Please leave it in. I've added it back with this wording: "As shown in the example below, in order to calculate the broadcast address to transmit a packet to an entire IPv4 subnet using the private IP address space 172.16.0.0/12, which has the subnet mask 255.240.0.0, the broadcast address is calculated as 172.16.0.0 bitwise ORed with 0.15.255.255 = 172.31.255.255." Also, I've moved the generic information which applies to *any* example to be a standalone paragraph, rather than part of the intro do the example. This makes much more sense. ERCaGuy (talk) 22:26, 5 April 2020 (UTC)