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CSE 30264 Computer Networks

CSE 30264 Computer Networks. Prof. Aaron Striegel Department of Computer Science & Engineering University of Notre Dame Lecture 14 – February 23, 2010. Today’s Lecture. Mid-Term Exam Summary Project 2 Transport RPC Mid-Term Exam. Application. Transport. Network. Data. Physical.

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CSE 30264 Computer Networks

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  1. CSE 30264Computer Networks Prof. Aaron Striegel Department of Computer Science & Engineering University of Notre Dame Lecture 14 – February 23, 2010

  2. Today’s Lecture • Mid-Term Exam Summary • Project 2 • Transport • RPC • Mid-Term Exam Application Transport Network Data Physical Thursday: Guest lecture by Dr. Poellabauer CSE 30264

  3. Mid-Term Exam • Will hand out later in class • Average -> 83% • Maximum points: 104 • Want to earn back points? • Pick one problem • Well written, well illustrated discussion of the problem • Gain back up to half of points lost on that problem CSE 30264

  4. Project 2 • By popular demand • Turn in by Tuesday, March 23 @ 5 PM • Wiki will update later today • Extra credit • Bonus 10 points • Turn in by Thursday, March 18 @ 5 PM • Add note in README • Down side • Project 3 is coming next Tuesday CSE 30264

  5. Tip / Tricks – Project 2 • Split your code into blocks and test separately • Send as a file Client Test Open up socket Connect to server Read file from disk Send buffer to server Read response Display to screen CSE 30264

  6. Tips / Tricks – Project 2 • Split your code • Write your handler in a thread friendly void * handleClient (void * pData) { intclientSocket; nClientSocket = *( (int *) pData); // Handle client CSE 30264

  7. Tips / Tricks – Project 2 • Split your code • Write your handler in a thread friendly int main ( … ) { // Server socket magic // Listen while(1) { cSocket = accept (…); handleClient(&cSocket); CSE 30264

  8. Tips / Tricks – Project 2 • Split your code • Test your XML parsing separately • Read in a file and parse the results • Go simple XML <xml version … /> <add CalName=“Test” Month=“3” Day=“16” … /> CSE 30264

  9. Project 2 – Other Notes • Client side • Support two modes • Send the file and display the response (easier) • Respond to arguments / build XML • You can write two different clients if that makes things easier • Server side • Your server does not need to persist data after restart • Files / storage are great but not required • You could have two different servers as well, one for multi-thread, one for single thread CSE 30264

  10. Remote Procedure Call Outline Concept of RPC SunRPC CSE30264

  11. RPC Timeline CSE30264

  12. RPC • There exists a way for processes to represent a task: procedure/function. Client main() main() return 5; func(12); return 5; func(12); Server func() func() CSE30264

  13. RPC Client main() stub(12); return 5; stub Request Reply Server skeleton func(12); return 5; func() CSE30264

  14. Stubs • Stub is a function with the same interface as func(); it converts the function call into a network response and a network response into a function return. • Skeleton converts requests into function calls and function returns into network replies. • RPC System: used to generate both stub and skeleton (automatically). CSE30264

  15. SunRPC • Widely used Remote Procedure Call system: • Sun Microsystems, implemented in most Unix systems • NFS distributed file system is based on Sun RPC • Designed to call remote C procedures. • Platform-independent. CSE30264

  16. SunRPC Header Format • XID (transaction id) • Server does not remember last XID it serviced • Problem if client retransmits request while reply is in transit CSE30264

  17. RPC • One computer can be server for multiple procedures: • server may host several programs (identified by program number) • each program may have several subsequent versions (version number) • each version may contain one or more procedures (procedure number) • Program numbers are 32-bit hexadecimal values (0x21212100) • As user, you can choose any program number between 0x20000000 and 0x3FFFFFFF, but they have to be unique (not several programs with same number on same machine) • Version and procedure numbers are integers (1,2,...) (prog, vers, proc) CSE30264

  18. Sun RPC Program Numbers FROM TO VALUES ASSIGNED BY 0x00000000 0x1fffffff Sun Microsystems, Inc. 0x20000000 0x3fffffff System manager at a user’s site 0x40000000 0x5fffffff Transient (temporary) 0x60000000 0x7fffffff Reserved 0x80000000 0x9fffffff Reserved 0xa0000000 0xbfffffff Reserved 0xc0000000 0xdfffffff Reserved 0xe0000000 0xffffffff Reserved CSE30264

  19. Sun RPC Program Numbers NAME NUMBER DESCRIPTION portmap 100000 port mapper rstatd 100001 rstat, rup, perfmeter rusersd 100002 remote users nfs 100003 network file system ypserv 100004 yp (NIS) mountd 100005 mount, showmount dbxd 100006 DMXprog (debugger) ypbind 100007 NIS binder ... CSE30264

  20. Writing an RPC Program client.c client.o add_clnt.c add_clnt.o client add.h add.x add_xdr.c add_xdr.o add_scv.c add_svc.o server You obtain a client & server serverproc.c serverproc.o You write these files rpcgen generates these files You compile every C file CSE30264

  21. Example • Step 1: Write a specification file (add.x) structadd_in { /* Arguments of procedure */ long arg1; long arg2; }; typedef long add_out; /* Return value */ program ADD_PROG { version ADD_VERS { add_out ADD_PROC(add_in) = 1 /* Procedure# = 1 */ } = 1; /* Version# = 1 */ } = 0x3434000; /* Program# = 0x3434000 */ CSE30264

  22. Example • Contains specifications of: • ‘add_in’ (arguments) • typedef ‘add_out’ (return values) • program ‘ADD_PROG’ (0x3434000) • 1 version ‘ADD_VERS’ (1) • 1 procedure ‘ADD_PROC’ (1) • Your procedures can only take ONE input argument and return ONE output return value (use structures for more): • more readable (structure entries should have meaningful names) CSE30264

  23. Example • Step 2: generate stubs rpcgen add.x • ‘add.h’ contains declarations: #define ADD_PROG 0x34340000 /* Program nb */ #define ADD_VERS 1 /* Version nb */ #define ADD_PROC 1 /* Procedure nb */ add_out * add_proc_1 (add_in *, CLIENT *); add_out * add_proc_1_svc (add_in *, struct svc_req *); • add_proc_1 is the stub (called by client) • add_proc_1_svc is the actual procedure that you will write and run at the server CSE30264

  24. Example • ‘add_clnt.c’: implementation of ‘add_proc_1’ • ‘add_svc.c’: contains program which calls your procedure ‘add_proc_1_svc’ when request received • ‘add_xdr.c’: marshall/unmarshall routines CSE30264

  25. Example • Step 3: write server procedure: ‘serverproc.c’ #include “add.h” add_out *add_proc_1_svc(add_in *in, struct svc_req *rqstp) { static add_out out; out = in->arg1 + in->arg2; return(&out); } • rqstp contains some information about the requester (IP address, etc.) CSE30264

  26. Example • Step 4: compile the server • Need to compile together your procedure, the (generated) server program, the (generated) marshall/unmarshall procedures and the nsl library (contains the RPC runtime). $ gcc -c serverproc.c $ gcc -c add_svc.c $ gcc -c add_xdr.c $ gcc -o server serverproc.o add_svc.o add_xdr.o -lnsl • To start the server: ./server CSE30264

  27. Example • Step 5: write a client program client.c #include “add.h” int main(intargc, char **argv) { CLIENT *cl; add_in in; add_out *out; if (argc!=4) {printf(“Usage:...\n”); return 1;} cl = clnt_create(argv[1], ADD_PROG, ADD_VERS, “tcp”); in.arg1 = atol(argv[2]); in.arg2 = atol(argv[3]); out = add_proc_1(&in, cl); if (out == NULL) {printf(“Error: %s\n”, clnt_sperror(cl, argv[1])); } else { printf{“We received the result: %ld\n”, * out); } clnt_destroy(cl); return 0; } CSE30264

  28. Example • Create a client structure with clnt_create #include <rpc/rpc.h> CLIENT *clnt_create(char *host, u_long prog, u_long vers, char *proto); • host: name of server machine • prog, vers: program/version number • proto: transport protocol (“tcp” or “udp”) • You can call add_proc_1 to send the RPC • When finished, destroy client structure (client structure can be used multiple times without being destroyed and recreated). CSE30264

  29. Example • Step 6: compile the client $ gcc -c client.c $ gcc -c add_clnt.c $ gcc -c add_xdr.c $ gcc -o client client.o add_clnt.o add_xdr.o -lnsl CSE30264

  30. Example • Step 7: try it out • start your server: ./server • send a request: ./client machine.cse.nd.edu 8 34 We received the result: 42 CSE30264

  31. Mutual Exclusion • Sun RPC: at most one remote procedure in a remote program can be invoked at a given time. • Automatic mutual exclusion among procedures within a given remote program. • No synchronization needed. • Some versions of rpcgen allow one to generate server code which implement one-thread-per-client (Solaris does, Linux doesn’t). CSE30264

  32. Inside SunRPC Client Server client program server procedure (un)marshalling routines (un)marshalling routines client stub server stub RPC runtime RPC runtime CSE30264

  33. Low-Level RPC: Port Mapper • Did you notice that we did not specify a port number for our ‘add’ server? • Could be done with well-known port number for RPCs • But then we could not run multiple servers in the same machine simultaneously • RPC: port mapper • server running on port 111 • when your server starts, it does not bind its socket to a specific port; instead it ‘registers’ whatever port number it has been given by the system to the local port mapper • when you create a client with ‘clnt_create’, you automatically contact the remote port mapper to ask for the port number of the server you want to contact CSE30264

  34. Port Mapper S5: Run procedure 1 with parameter: “0x18A6B332F0” S1: Create an unbound socket (assigned port=11293) Client Server S6: Result is “0x6464” S2: Register: program 0x3434000 version 1 running on port 11293 S4: Portmap response: port 11293 S3: Portmap requested: on which port is program 0x3434000 version 1? Port mapper • You can request the port mapper by hand: • $ rpcinfo -p wizard.cse.nd.edu • program vers proto port • 100000 2 tcp 111 portmapper • 100000 2 udp 111 portmapper • 66443998 1 udp 32877 • 66443938 1 tcp 54211 CSE30264

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