有關於 Broadcast 的疑惑

[-Hero-]

請問各位網路高手，
Broadcast大家都聽過，
那有人知道其原理與詳細的情形嗎？

[conankun]

嗯........
1.網路七層架構
2.tcp/ip通訊協定
看完那兩個後就可以了
用打的有點多 ^^||

[milwater]

同上(觀念粉多,慢慢來吧).
不過倒是可以給你個小hint:
網路上的傳播方式大抵可以分為三類:
1.Peer-to-peer - 對等傳送, 為單對單的訊號傳遞.
2.Multicast - 多向傳送, 為單對多的訊號傳遞.
3.Broadcast - 廣播傳送, 為單對全的訊號傳遞.
而每個不同的網路服務可搭配不同的網路傳播方式,
例如TCP常用P2P,UDP常用Broadcast. 大約如此囉~

[-Hero-]

最初由 milwater
同上(觀念粉多,慢慢來吧).
不過倒是可以給你個小hint:
網路上的傳播方式大抵可以分為三類:
1.Peer-to-peer - 對等傳送, 為單對單的訊號傳遞.
2.Multicast - 多向傳送, 為單對多的訊號傳遞.
3.Broadcast - 廣播傳送, 為單對全的訊號傳遞.
而每個不同的網路服務可搭配不同的網路傳播方式,
例如TCP常用P2P,UDP常用Broadcast. 大約如此囉~

你說的我知道,
我所問的是,
Broadcsast是如何的廣播?
其方式?其原理?
其訊息傳送的方式?
其routing?

[Lettuce]

以TCP/IP為例...
若!!
您的IP..區段
192.168.1.0/29
Netmask即為
255.255.255.248
那..可用IP即為8個..
192.168.1.0 <- Network Address
192.168.1.1
192.168.1.2
192.168.1.3
192.168.1.4
192.168.1.5
192.168.1.6
192.168.1.7 <- Boardcast Address
現以您的問題..
來說明一下簡單的Boardcast原理..
當您在對您的區域網路做Boardcast的動作時...(別問我怎麼做... -_-"" )
會傳送一個封包至192.168.1.8的位址...
在經由他轉送到192.168.1.1至192.168.1.6..
至於..最常見得Boardcast動作呢...
就是在您打開"網路上的芳鄰"時....系統會去做的動做..
不知道..這樣回答了您的問題了嗎???

[segaage]

最初由 herozero

你說的我知道,
我所問的是,
Broadcsast是如何的廣播?
其方式?其原理?
其訊息傳送的方式?
其routing?

Hi herozero兄:
大致上,想了解broadcast的運作方式,小弟建議使用win nt或2k,xp中內附的網路
監視器,效果絕佳!
首先:
1.廣播封包在傳送時,和一般封包不同的是:其目的mac位址全數為0和一般封包不
同(已指定1個特定的位址)
2.因為1.的關係(mac)造成網路上所有的主機都必須收此封包,並檢查看此封包是
否有要處理的資訊,如沒有則直接捨棄,有的話就會依封包內容回應資料回來源端
mac位址
3.由2.中得知:因所有主機都要處理廣播封包,所以和路由無關,又因來源端會一直
發送廣播封包直到收到回應為止(當然必須看服務項目為何,例dhcp等等)若此封包
發送太多將形成廣播風暴造成網路癱瘓,這就是為何路由器要阻擋廣播封包的原因
不知這樣post有無解決herozero兄的問題?另若文中有誤,尚請各位先進能不吝指正
,謝謝!

[conankun]

Network Layers
In order to understand the way NFS functions, it is important to have some understanding of the functions of the lower network layers. The standard model for networking protocols and distributed applications is the International Standard Organization's Open System Interconnect (ISO/OSI) model. It defines seven network layers.

Layer 1 - Physical

Physical layer defines the cable or physical medium itself, e.g., thinnet, thicknet, unshielded twisted pairs (UTP). All media are functionally equivalent. The main difference is in convenience and cost of installation and maintenance. Converters from one media to another operate at this level.

Layer 2 - Data Link

Data Link layer defines the format of data on the network. A network data frame, aka packet, includes checksum, source and destination address, and data. The largest packet that can be sent through a data link layer defines the Maximum Transmission Unit (MTU). The data link layer handles the physical and logical connections to the packet's destination, using a network interface. An host connected to an Ethernet would have an Ethernet interface to handle connections to the outside world, and a loopback interface to send packets to itself.
Ethernet addresses a host using a unique, 48-bit address called its Ethernet address or Media Access Control (MAC) address. MAC addresses are usually represented as six colon-separated pairs of hex digits, e.g., 8:0:20:11:ac:85. This number is unique and is associated with a particular Ethernet device. Hosts with multiple network interfaces should use the same MAC address on each. The data link layer's protocol-specific header specifies the MAC address of the packet's source and destination. When a packet is sent to all hosts (broadcast), a special MAC address (ff:ff:ff:ff:ff:ff) is used.

Layer 3 - Network

NFS uses Internetwork Protocol (IP) as its network layer interface. IP is responsible for routing, directing datagrams from one one network to another. Network layer may have to break large datagrams, larger than MTU, into smaller packets and host receiving the packet will have to reassemble the fragmented datagram. The Internetwork Protocol identifies each host with a 32-bit IP address. IP addresses are written as four dot-separated decimal numbers between 0 and 255, e.g., 129.79.16.40. The leading 1-3 bytes of the IP identifies the network and the remaining bytes identifies the host on that network. The network portion of the IP is assigned by InterNIC Registration Services, under the contract to the National Science Foundation, and the host portion of the IP is assigned by the local network administrators, locally by [email protected]. For large sites, usually subnetted like ours, the first two bytes represents the network portion of the IP, and the third and fourth bytes identify the subnet and host respectively.
Even though IP packets are addressed using IP addresses, hardware addresses must be used to actually transport data from one host to another. The Address Resolution Protocol (ARP) is used to map the IP address to it hardware address.

Layer 4 - Transport

Transport layer subdivides user-buffer into network-buffer sized datagrams and enforces desired transmission control. Two transport protocols, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), sits at the transport layer. Reliability and speed are the primary difference between these two protocols. TCP establishes connections between two hosts on the network through 'sockets' which are determined by the IP address and port port number. TCP keeps track of the packet delivery order and the packets that must be resent. Maintaining this information for each connection makes TCP a statefull protocol. UDP on the other hand provides a low overhead transmission service, but with less error checking. NFS is built on top of UDP because of its speed and statelessness. Statelessness simplifies the crash recovery.

Layer 5 - Session

The session protocol defines the format of the data sent over the connections. The NFS uses the Remote Procedure Call (RPC) for its session protocol. RPC may be built on either TCP or UDP. Login sessions uses TCP where as NFS and broadcast use UDP.

Layer 6 - Presentation

External Data Representation (XDR) sits at the presentation level. It converts local representation of data to its canonical form and vice versa. The canonical uses a standard byte ordering and structure packing convention, independent of the host.

Layer 7 - Application

Provides network services to the end-users. Mail, ftp, telnet, DNS, NIS, NFS are examples of network applications.

[-Hero-]

最初由 segaage

Hi herozero兄:
大致上,想了解broadcast的運作方式,小弟建議使用win nt或2k,xp中內附的網路
監視器,效果絕佳!
首先:
1.廣播封包在傳送時,和一般封包不同的是:其目的mac位址全數為0和一般封包不
同(已指定1個特定的位址)
2.因為1.的關係(mac)造成網路上所有的主機都必須收此封包,並檢查看此封包是
否有要處理的資訊,如沒有則直接捨棄,有的話就會依封包內容回應資料回來源端
mac位址
3.由2.中得知:因所有主機都要處理廣播封包,所以和路由無關,又因來源端會一直
發送廣播封包直到收到回應為止(當然必須看服務項目為何,例dhcp等等)若此封包
發送太多將形成廣播風暴造成網路癱瘓,這就是為何路由器要阻擋廣播封包的原因
不知這樣post有無解決herozero兄的問題?另若文中有誤,尚請各位先進能不吝指正
,謝謝!

首先謝謝Lettuce和segaage的回答,
因為你們的回覆使我又增進了不少見識,
我現在想知道的是再深入的;
也就是Broadcast的動作,
網路上有許多節點,
某台broadcast
那他的傳送方式又是如何呢?
是如何的傳送讓所有節點上的PC都收到呢?

[-Hero-]

最初由 segaage

Hi herozero兄:
大致上,想了解broadcast的運作方式,小弟建議使用win nt或2k,xp中內附的網路
監視器,效果絕佳!
首先:
1.廣播封包在傳送時,和一般封包不同的是:其目的mac位址全數為0和一般封包不
同(已指定1個特定的位址)
2.因為1.的關係(mac)造成網路上所有的主機都必須收此封包,並檢查看此封包是
否有要處理的資訊,如沒有則直接捨棄,有的話就會依封包內容回應資料回來源端
mac位址
3.由2.中得知:因所有主機都要處理廣播封包,所以和路由無關,又因來源端會一直
發送廣播封包直到收到回應為止(當然必須看服務項目為何,例dhcp等等)若此封包
發送太多將形成廣播風暴造成網路癱瘓,這就是為何路由器要阻擋廣播封包的原因
不知這樣post有無解決herozero兄的問題?另若文中有誤,尚請各位先進能不吝指正
,謝謝!

收封包的包括發送的自己嗎?

[segaage]

最初由 herozero

首先謝謝Lettuce和segaage的回答,
因為你們的回覆使我又增進了不少見識,
我現在想知道的是再深入的;
也就是Broadcast的動作,
網路上有許多節點,
某台broadcast
那他的傳送方式又是如何呢?
是如何的傳送讓所有節點上的PC都收到呢?

Hi herozero兄:
小弟所學有限,問得這麼深入恐已無力回答,建議至思科的網站去挖寶,相信會找到答案才是,另herozero兄問及broadcast的來源端是否會收到自己送出的封包,不妨這麼想:
上課時遇到外號為"點名魔"的老師,當其點名時,叫到的學生會回答為理所當然(老師本身也會聽見,但不是叫自己,沒有回答的必要)若叫了幾次都沒回應,便記曠課(當然和電腦不同的是:電腦不會因此出問題,頂多一直broadcast或request time out,但現實上該學科有被死當的可能)
最後要感謝conankun兄的指正