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<strong>TCL</strong> <strong>Scripting</strong> <strong>for</strong> <strong>Cisco</strong> <strong>IOS</strong>Petr Grygárekrek© 2009 Petr Grygarek, Advanced Computer Networks Technologies 1
Automation using <strong>TCL</strong> Scriptiong• Network monitoring• Troubleshooting tools• Added intelligence© 2009 Petr Grygarek, Advanced Computer Networks Technologies2
Tool Command Language (<strong>TCL</strong>)•Invented by John K. Ousterhout,Berkeley, 1980s•Interpreted language•support <strong>for</strong> compilation into bytecode•Runtime available <strong>for</strong> many plat<strong>for</strong>ms•http://www.tcl.tk/© 2009 Petr Grygarek, Advanced Computer Networks Technologies3
Tool Command Language (<strong>TCL</strong>)•Invented by John K. Ousterhout,Berkeley, 1980s, http://www.tcl.tk/•Interpreted language•support <strong>for</strong> compilation into bytecode•Intended <strong>for</strong> scripting, rapidprototyping, embedding intoapplications, creation of GUIs (<strong>TCL</strong>/Tktoolkit)•Runtime engine available <strong>for</strong> manyplat<strong>for</strong>ms© 2009 Petr Grygarek, Advanced Computer Networks Technologies4
<strong>TCL</strong> Basic Features(taken from http://en.wikipedia.org/wiki/Tcl)•Prefix command notation•variable number of arguments•No data types•all values treated as strings•Everything can be dynamically redefinedand overriden•Object-oriented extensions are available•Many extension libraries were developed© 2009 Petr Grygarek, Advanced Computer Networks Technologies5
•Applets<strong>IOS</strong> Policies•sequences of <strong>IOS</strong> commands•Stored in device's running config•<strong>TCL</strong> Scripts•Programs in <strong>TCL</strong>•Stored on FLASH or external storage•Policies are subscribed with EmbeddedEvent Manager (EEM) to be activatedwhen specific event(s) occur(s)•They also can be activated manually© 2009 Petr Grygarek, Advanced Computer Networks Technologies6
Embedded EventManager•Detects interesting events•using Event Detectors•Triggers specific policy based when aspecific event (or combination ofevents) occurs© 2009 Petr Grygarek, Advanced Computer Networks Technologies7
Event Detectors•Monitor SW and HW components <strong>for</strong>specific events•Examples of event detectors:•CLI,•Timer•Syslog•Object Tracking•interface state change detector•insertion/removal of module detector•...© 2009 Petr Grygarek, Advanced Computer Networks Technologies8
How to Execute <strong>TCL</strong>Script from <strong>Cisco</strong> <strong>IOS</strong>•tclsh flash0:myScript.tcl•<strong>TCL</strong> interactive shell mode: tclsh•Urecognized (i.e. non-<strong>TCL</strong>) commandsare passed to <strong>IOS</strong> CLI© 2009 Petr Grygarek, Advanced Computer Networks Technologies9
Basic <strong>TCL</strong> Commandsand Structures© 2009 Petr Grygarek, Advanced Computer Networks Technologies10
Getting Help•info commands•info exists •info args •info body •info globals•info varsCommand typed with wrong argument(s)make tclsh to display usage help# this is a comment© 2009 Petr Grygarek, Advanced Computer Networks Technologies11
set x 1puts $xAssignments, Expressions,Displaying Outputsset x [expr $x+1]puts $xincr x -10set p1 kocourset p2 mourset p3 "$p1 $p2" -> kocour mour© 2009 Petr Grygarek, Advanced Computer Networks Technologies12
“printf-like” OutputFormattingset a 1set s kocourset f [<strong>for</strong>mat "int: %d, string: %s" $a $s]f now contains “int: 1, string: kocour”Text in [] is replaced with result ofexecuted <strong>TCL</strong> code contained in block© 2009 Petr Grygarek, Advanced Computer Networks Technologies13
Arrays•Array is treated as set of associated pairs•no space pre-allocation•keys of any typeset a(1) 10set a(dog) Zerykputs $a(1) -> 10puts $a(dog) -> Zerykputs $a(2) -> can't read "a(2)": no such element in arrayarray set a “kocour mour number 2”puts $a(kocour) -> mourputs $a(number) -> 2© 2009 Petr Grygarek, Advanced Computer Networks Technologies15
Lists•List is a string consisting of valuesseparated by whitespaces.•List manipulation functions:•Llength,•lappend, linsert, lreplace, lrange•lindex, lsearch,•lsort© 2009 Petr Grygarek, Advanced Computer Networks Technologies18
Conditional Executionset x 1if {$x < 10} { puts LESS }else { puts GREATER }-> LESS© 2009 Petr Grygarek, Advanced Computer Networks Technologies20
set fd [open flash:f.txt w]puts $fd kocourputs $fd mourclose $fdRouter# more flash:f.txtset fd [open flash:f.txt r]Fileswhile { [gets $fd line] > 0 } { puts $line }close $fdtell $fd, seek $fd file e.g. file delete flash:f.txt© 2009 Petr Grygarek, Advanced Computer Networks Technologies22
Handling Script Argumentssample.tcl:puts "\n"puts "Argument count: $argc"puts "Argv0: $argv0"puts "Argv: $argv"puts "Individual arguments:"<strong>for</strong>each {iterVar} $argv { puts $iterVar }router #tclsh http://10.0.0.2/sample.tcl aaa bbb ccc-> Argument count: 3Argv0: http://10.0.0.2/kocour.tclArgv: aaa bbb cccIndividual arguments:aaabbbccc© 2009 Petr Grygarek, Advanced Computer Networks Technologies23
Interactions between <strong>TCL</strong>Policies and <strong>IOS</strong> CLI© 2009 Petr Grygarek, Advanced Computer Networks Technologies24
Running <strong>TCL</strong> Scripts•From <strong>TCL</strong> shell•“source” <strong>TCL</strong> commandrouter(tcl)#source flash:mysrc.tclrouter(tcl)#source http://10.0.0.2/kocour.tcl•From <strong>IOS</strong> exec mode•“tclsh” command followed by script namerouter#tclsh http://10.0.0.2/kocour.tcl args•Arguments cannot be passed to scriptusing source command•Multiple scripts may run in parallel.© 2009 Petr Grygarek, Advanced Computer Networks Technologies25
Exec Mode Commands•log_user 0/1 - disables/enables displayingof CLI commands outputs•set cliOutput [exec "sh ip interface brief"]– works both in interactive <strong>TCL</strong> shell and<strong>TCL</strong> scripts© 2009 Petr Grygarek, Advanced Computer Networks Technologies26
Config Mode Commands(<strong>TCL</strong> Shell)ios_config "hostname MYNAME"ios_config "router rip" "network10.0.0.0" "end"•It is recommended to exit from <strong>TCL</strong>shell <strong>for</strong> the configuration changes totake effect•Always end the configurationcommands with end to avoid locking© 2009 Petr Grygarek, Advanced Computer Networks Technologies27
Config Mode Commands(EEM <strong>TCL</strong> Policies)•FD-style functions•cli_open, cli_write, cli_read, cli_exec•cli_exec = cli_write + cli_read•Work in <strong>TCL</strong> scripts, NOT ininteractive <strong>TCL</strong> shell.•On the other hand, ios_config doesNOT work in <strong>TCL</strong> scripts (?)© 2009 Petr Grygarek, Advanced Computer Networks Technologies28
Dealing with InteractiveCommandsRouter(tcl)#typeahead \n\n\nRouter(tcl)#exec "copy run flash:x.x"•Does not work in <strong>TCL</strong> Shellinteractive mode•Alternative: file prompt quiet <strong>IOS</strong>comand© 2009 Petr Grygarek, Advanced Computer Networks Technologies29
Policy Registration with EEM•Either applet or <strong>TCL</strong> script may beregistered to be activated when anevent is detectedevent manager directory user policy flash:/scriptsevent manager policy myScript.tcl•Specification of the event to triggerthe policy is defined at the beginningof policy's <strong>TCL</strong> script:•::cisco::eem::event_register_timer cron namemyCron1 cron_entry "0-59 0-23 * * 0-7"© 2009 Petr Grygarek, Advanced Computer Networks Technologies30
Checking Registered Policies•show event manager policy available[user | system]•show event manager policyregistered•sh event manager history eventEEM policies have to be stored on some localfilesystem to ensure their availability regardless ofthe current state of the connectivity to anyexternal storage server.© 2009 Petr Grygarek, Advanced Computer Networks Technologies31
Manual Policy Launching•event manager run myScript.tcl•only applicable <strong>for</strong> policies registeredwith none event© 2009 Petr Grygarek, Advanced Computer Networks Technologies32
Specification of Policy'sEnvironment•Router(config)#event managerenvironment myVariable myValue•Router(config)#event managersession cli username kocour•sh event manager session cliusername© 2009 Petr Grygarek, Advanced Computer Networks Technologies33
Example Policy(launched manually)::cisco::eem::event_register_nonenamespace import ::cisco::eem::*namespace import ::cisco::lib::*array set cliconn [ cli_open ]puts $cliconncli_exec $cliconn(fd) "hostnameCHANGED-NAME"cli_close $cliconn(fd)© 2009 Petr Grygarek, Advanced Computer Networks Technologies34
EEM Applets•Definition consists of•Events to be detected to trigger theapplet•available events may vary with different <strong>IOS</strong>/EEM versions•Sequence of <strong>IOS</strong> commands to beexecuted•Sorted lexicographically according to linetags© 2009 Petr Grygarek, Advanced Computer Networks Technologies35
Most Interesting SupportedFeatures (1)• Reaction to composite events• Reacting to interface status change• Processing of RIB change events• Reacting to <strong>IOS</strong> object status change•Enhanced Object Tracking• Reacting to Syslog messages• Reacting to increased resource utilization (CPU,memory, ...)• Integration with SLA monitoring• Timers & Counters events© 2009 Petr Grygarek, Advanced Computer Networks Technologies36
Most Interesting SupportedFeatures (2)• Sockets Library• SNMP Library (outgoing/incoming messages)• SMTP Library• Integration with Netflow• CLI library & events•issuing <strong>IOS</strong> exec and config commands•interception of command handling process•creation of user commands and/or extendingcommand parameters© 2009 Petr Grygarek, Advanced Computer Networks Technologies37
Most Interesting SupportedFeatures (3)• Messaging between policies running in parallel,policy synchronization• Policy priorization•multiple scheduling queues, nice, ...• Persistent storage to keep script's internal statebetween runs• Remote Procedure Call (RPC)• XML-PI• <strong>TCL</strong> scripts debugging support© 2009 Petr Grygarek, Advanced Computer Networks Technologies38
References•Summarized athttp://wh.cs.vsb.cz/sps/index.php/<strong>TCL</strong>_scripting_on_<strong>Cisco</strong>_<strong>IOS</strong>© 2009 Petr Grygarek, Advanced Computer Networks Technologies39
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