Packet flow in Netfilter and General Networking (Linux)

ref. http://upload.wikimedia.org/wikipedia/commons/3/37/Netfilter-packet-flow.svg

linux 網路設定

修改的參數	設定檔與重要啟動腳本	觀察結果的指令
IP相關參數	/etc/sysconfig/network-scripts/ifcfg-eth0 /etc/init.d/network restart	ifconfig (IP/Netmask) route -n (gateway)
DNS	/etc/resolv.conf	dig www.google.com
主機名稱	/etc/sysconfig/network /etc/hosts	hostname (主機名) ping $(hostname) reboot

TR-069 CPE 和 ACS 之間溝通的通訊協

WIKI

http://www.mem.com.tw/article_content.asp?sn=1001260014

linux 指令 brctl

如何在 Linux 底下建立橋接介面給虛擬機器使用http://pominglee.blogspot.tw/2014/03/linux.html
本文

ref. http://my.oschina.net/guol/blog/69599

http://fp-moon.iteye.com/blog/1468650

linux 網路相關指令 ifconfig / route / ping / traceroute / netstat

每天一个linux命令（52）：ifconfig命令 

.每天一个linux命令（53）：route命令

每天一个linux命令（54）：ping命令

每天一个linux命令（55）：traceroute命令

每天一个linux命令（56）：netstat命令

c/c++ 演算法技巧

今天看code 看到一個莫名其妙的東西，上網搜尋一下

unsigned popcount (unsigned u)
{
u = (u & 0x55555555) + ((u >> 1) & 0x55555555);
u = (u & 0x33333333) + ((u >> 2) & 0x33333333);
u = (u & 0x0F0F0F0F) + ((u >> 4) & 0x0F0F0F0F);
u = (u & 0x00FF00FF) + ((u >> 8) & 0x00FF00FF);
u = (u & 0x0000FFFF) + ((u >> 16) & 0x0000FFFF);
return u;
}

原來是個不知為何的演算法得出來的結果，原理大概是查表，此用法只適用於32位無號整數，目的是在算input u 總共有幾個bit為1，稍微紀錄一下。

=> 使用分治法
https://zh.wikipedia.org/wiki/%E6%B1%89%E6%98%8E%E9%87%8D%E9%87%8F

簡單來說就是先算出兩個bit裡面有幾個1
A=b'1111
(A) &(b'0101) +(A>>1)&(b'0101) =b'1010 
代表第
0,1 bit 有兩個為1 
2,3bit 有兩個為1
接著就是 shift跟加法的問題



ref.

http://blog.csdn.net/rappy/article/details/1788969

How many bytes in a packet?

Sometime, we found some devices that point out "forwarding rate, Mpps". The "pps" is the short term for packet per second. However, how many bytes in a packet? It depends, there is no specification on how many byte in a packet, you define it by yourself.

In the 100M Ethernet network,
100M bps / 8 = 12.5 MBps = 12500000 Bytes/s(Bps)

If you define the frame size is 64 Bytes (Minimum Ethernet framz size):
8 Bytes (preamble) + 64 Bytes + 12 Bytes (interframe gap) = 84 Bytes

So forwarding rate will be
12500000 Bps / 84 bytes = 148809 pps

If you define the frame size is 1518 Bytes (Maximum Ethernet framz size):
8 Bytes (preamble) + 1518 Bytes + 12 Bytes (interframe gap) = 1538 Bytes

So forwarding rate will be
12500000 Bps / 1538 bytes = 8127 pps

100M Ethernet's forwarding rate formula:
12500000 Bps / ( 8 Bytes (preamble) + (Feame Size) + 12 Bytes (interframe gap)) = forwarding rate, pps

c/c++ 運算子優先順序

優先 符號                                     運算種類                         結合

---- ----------------------                   -------------                       ------

1     ( ) [ ] -> .                                運算式                             左至右

2     ! ～ ++ -- -                             (運算元) 一元運算子     右至左

        * & sizeof

3     * / %                                       乘/除/餘數                      左至右

4     + -                                           加/減                               左至右

5     << >>                                      左移/右移                       左至右

6     < <= > >=                               關係運算子                    左至右

7     == !=                                      關係運算子                    左至右

8     &                                            位元 AND                       左至右

9     ^                                             位元 XOR                       左至右

10    |                                             位元 OR                          左至右

11   &&                                         邏輯 AND                       左至右

12   ||                                             邏輯 OR                          左至右

13   ?:                                            條件運算子                    右至左

14   = += -= *= /= %=                  指定運算子                    右至左

        <<= >>= &= |= ^=

15   ,                                              循序計值                        左至右

SVN externals 屬性 依賴 外部連結

快速
http://blog.csdn.net/echoisland/article/details/6584875

詳細
https://cylin.wordpress.com/2007/10/08/svnexternals%E5%B1%AC%E6%80%A7%E4%B9%8B%E4%BD%BF%E7%94%A8/

//windows 操作
http://ccd9527.blogspot.tw/2010/06/svnexternals.html
https://help.cloudforge.com/entries/22483742-Setting-up-svn-externals

原文
http://svnbook.red-bean.com/nightly/en/svn.advanced.externals.html

linux networking netfilter

netfilter

http://blog.csdn.net/qy532846454/article/details/8255728