Linux 網路封包處理流程

pppoe-relay

NAME

pppoe-relay - user-space PPPoE relay agent.  

SYNOPSIS

pppoe-relay [options]  

DESCRIPTION

pppoe-relay is a user-space relay agent for PPPoE (Point-to-Point Protocol over Ethernet) for Linux. pppoe-relay works in concert with the pppoe client and pppoe-server server. See the OPERATION section later in this manual for details on how pppoe-relay works.  

OPTIONS

-S interface

Adds the Ethernet interface interface to the list of interfaces managed by pppoe-relay. Only PPPoE servers may be connected to this interface.

-C interface

Adds the Ethernet interface interface to the list of interfaces managed by pppoe-relay. Only PPPoE clients may be connected to this interface.

-B interface

Adds the Ethernet interface interface to the list of interfaces managed by pppoe-relay. Both PPPoE clients and servers may be connected to this interface.

-n num

Allows at most num concurrent PPPoE sessions. If not specified, the default is 5000. num can range from 1 to 65534.

-i timeout

Specifies the session idle timeout. If both peers in a session are idle for more than timeout seconds, the session is terminated. If timeout is specified as zero, sessions will never be terminated because of idleness. Note that the idle-session expiry routine is never run more frequently than every 30 seconds, so the timeout is approximate. The default value for timeout is 600 seconds (10 minutes.)

-F

The -F option causes pppoe-relay not to fork into the background; instead, it remains in the foreground.

-h

The -h option prints a brief usage message and exits.

 

OPERATION

pppoe-relay listens for incoming PPPoE PADI frames on all interfaces specified with -B or -C options. When a PADI frame appears, pppoe-relay adds a Relay-Session-ID tag and broadcasts the PADI on all interfaces specified with -B or -S options (except the interface on which the frame arrived.)
Any PADO frames received are relayed back to the client which sent the PADI (assuming they contain valid Relay-Session-ID tags.) Likewise, PADR frames from clients are relayed back to the matching access concentrator.
When a PADS frame is received, pppoe-relay enters the two peers' MAC addresses and session-ID's into a hash table. (The session-ID seen by the access concentrator may be different from that seen by the client; pppoe-relay must renumber sessions to avoid the possibility of duplicate session-ID's.) Whenever either peer sends a session frame, pppoe-relay looks up the session entry in the hash table and relays the frame to the correct peer.
When a PADT frame is received, pppoe-relay relays it to the peer and deletes the session entry from its hash table.
If a client and server crash (or frames are lost), PADT frames may never be sent, and pppoe-relay's hash table can fill up with stale sessions. Therefore, a session-cleaning routine runs periodically, and removes old sessions from the hash table. A session is considered "old" if no traffic has been seen within timeout seconds. When a session is deleted because of a timeout, a PADT frame is sent to each peer to make certain that they are aware the session has been killed.
 

EXAMPLE INVOCATIONS

pppoe-relay -C eth0 -S eth1

The example above relays frames between PPPoE clients on the eth0 network and PPPoE servers on the eth1 network.

pppoe-relay -B eth0 -B eth1

This example is a transparent relay -- frames are relayed between any mix of clients and servers on the eth0 and eth1 networks.

pppoe-relay -S eth0 -C eth1 -C eth2 -C eth3

This example relays frames between servers on the eth0 network and clients on the eth1, eth2 and eth3 networks.

Xming

要在Windows底下登入遠端Linux系統並進行操作需要安裝下列軟體：

1.      Xming 和 Xming-fonts  (http://www.straightrunning.com/XmingNotes)

2.      Putty              (http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html)

Part I：使用XDMCP
我們要將遠端主機以圖形介面開回自己的桌面上，
首先先執行Putty，它是一個連線軟體，
在左手邊的選單中找到SSH -> X11，
將Enable X11 forwarding 打勾
並在 X display location 這行輸入： localhost:0
然後再開啟Xming

我們選 Fullscreen，
底下的Display number則維持在0就好
(注意：若將Display number的數字更動，則Putty的X display location這行的
 localhost:0 數字0的地方也需要跟著更動)

這邊選第三個 Open session via XDMCP

Connect to host 則輸入你想要登入的主機IP  (欲登入的主機須先設定XDMCP)

這邊按下一步就好

這邊可以儲存你剛剛的設定，以後只要直接執行設定檔就可以了

按下完成後，就會以全螢幕的方式登入到遠端的主機，
打入帳號密碼以後，就可以在自己的桌面上控制遠端主機了

只要該主機有支援的功能，都可以控制它去執行哦

注意事項：

1.      欲登入的主機需事先開啟XDMCP的功能

2.      本地主機需安裝Xming與Putty

3.      先執行Putty再Xming

4.      Putty需留在桌面上執行，不能關閉

Part II：不使用XDMCP
使用圖形介面來操控遠端主機比較耗系統資源，如果我們已經熟悉Linux的指令，那麼不妨直接使用指令來操作還比較方便，底下將介紹不使用XDMCP透過Xming連到遠端主機的方法。


首先開啟Xming，這次我們選擇One window，

 
選擇Start a program

選Using PuTTY，並輸入欲登入主機的IP與你的帳號

直接下一步

可先儲存你的設定，下一次就直接執行儲存檔就好

按下完成就會跳出下列要求輸入密碼的畫面，
輸入密碼以後就登入了遠端主機

熟悉指令的人就可以直接以下指令的方式來操控遠端主機了

from https://sites.google.com/site/ykcycuee/tutorial/Home

lrzsz: free x/y/zmodem implementation

lrzsz is a unix communication package providing the XMODEM, YMODEM ZMODEM file transfer protocols. lrzsz is a heavily rehacked version of the last public domain release of Omen Technologies rzsz package, and is now free software and released under the GNU General Public Licence.

---

Features of lrzsz

• very portable, automagically configured with GNU autoconf.
• crash recovery.
• up to 8KB block sizes (ZMODEM8K).
• internationalized (using GNU gettext). German translation of the programs output exists.
• far more secure than the original sources.
• high performance. say `make vcheck-z' and have a look at the BPS rate - i recently saw 1.4 MB per second transfering a large file through pipes (on a I586/133 system. Beat that!).
• good blocksize calculation (tries to compute an optimal blocksize based on the number of errors occured).
• It's free software.

---

Downloading lrzsz

The lastest release is lrzsz-0.12.20.tar.gz ((about 270KB)).

SSH Client — Xshell

Xshell 是一個 Windows 平台下的終端機模擬器，支援 SSH1, SSH2, SFTP, TELNET, RLOGIN, SERIAL。不用 Putty 的理由是因為 Xshell 可以同時開啟多 session，在管理數台伺服器上方便很多。Xshell 是付費軟件，但如果個人使用則免費。

Xshell 官方網站

 

Git cheat sheet, extended edition

http://jan-krueger.net/wordpress/wp-content/uploads/2007/09/git-cheat-sheet-v2.zip

Makefile 常見phoney target

make all

產生我們設定的目標，即此範例中的執行檔。只打 make 也可以，此時會開始編譯原始碼，然後連結，並且產生執行檔。

make clean

清除之前所編譯的執行檔及目的檔 (object file, *.o)。

make distclean

除了清除執行檔和目的檔外，也把 configure 所產生的 Makefile也清除掉。

make install

將程式安裝至系統中。如果原始碼編譯無誤，且執行結果正確，便可以把程式安裝至系統預設的執行檔存放路徑。如果我們用bin_PROGRAMS 巨集的話，程式會被安裝至 /usr/local/bin 這個目錄。

make dist

將程式和相關的檔案包裝成一個壓縮檔以供散播 (distribution) 。執行完在目錄下會產生一個以 PACKAGE-VERSION.tar.gz 為名稱的檔案。PACKAGE 和 VERSION 這兩個變數是根據 configure.in 檔中
AM_INIT_AUTOMAKE(PACKAGE, VERSION) 的定義。在此範例中會產生'hello-1.0.tar.gz' 的檔案。

make distcheck

和 make dist 類似，但是加入檢查包裝後的壓縮檔是否正常。這個目標除了把程式和相關檔案包裝成 tar.gz 檔外，還會自動把這個壓縮檔解開，執行 configure，並且進行 make all 的動作，確認編譯無誤後，會顯示這個 tar.gz 檔已經準備好可供散播了。這個檢查非常有用，檢查過關的套件，基本上可以給任何一個具備 GNU 發展環境的人去重新編譯。就 hello-1.tar.gz 這個範例而言，除了在 RedHat Linux 上，在 FreeBSD 2.2.x 版也可以正確地重新編譯。