Oct 15 2008 - i almost forgot i even dabbled a little in tcl to aid my network engineering pursuits. Here i am using the event manager environment capabilities on higher end cisco IOS-based devices to monitor link status and set up alerts

linkmon.tcl

::cisco::eem::event_register_timer watchdog name linkmon time $linkmon_period maxrun 45
# _________________________________________________________________________#
# |                                                                       |#
# | cogent-monitor                                                        |#
# |                                                                       |#
# | by: Alex Koralewski                                                   |#
# | (c) 2008, Forex Capital Markets, LLC.                                 |#
# |                                                                       |#
# | Version 0.8 03/14/2008                                                |#
# | Version 1.0 04/03/2008                                                |#
# |_______________________________________________________________________|#
# 
# linkmon - timed link monitor
#
# desc:     The purpose is to monitor the packet loss based on the output 
#           of the ping command, if packet loss found, we will set delay on the
#           interface higher so the link is avoided
#
# trigger:  Watchdog timer - set from env variable
# action:   raise delay metric, send email
# env vars: linkmon_period - time interval for execution (seconds)
#           linkmon_int - interface to monitor
#           linkmon_ip_dest - ip address to ping
#           linkmon_ip_src - ip address to source ping packets from
#           
# restrictions:
#
#           To change execution interval or other parms, you must re-register 
#           the policy.
#
#           The policy will continue indefinitely once registered. 
#
# ios config:
#
#      linkmon setup:
#
#           Router#copy ftp://10.60.4.131/link-monitor.eem-script.tcl disk0:/linkmon.tcl
#           Router(config)#event manager directory user policy disk0:/
#           Router(config)#event manager environment linkmon_period 15
#           Router(config)#event manager environment linkmon_addr_dst 10.0.12.11
#           Router(config)#event manager environment linkmon_addr_src 10.0.12.1
#           Router(config)#event manager environment linkmon_int GigabitEthernet3/12
#
#	optionally, setting this will cause this neighbor to be cleared when the interface's delay is raised
#           Router(config)#event manager environment linkmon_eigrp_neighbor 10.0.12.11
#
#      linkmon enable:
#
#           Router(config)#event manager policy linkmon.tcl type user
#
#      linkmon disable
#
#           Router(config)#no event manager policy linkmon.tcl type user

# Check for required environment variables
# If any required vars are not available, print error and quit
if {![info exists linkmon_period]} {
    set result "EEM Policy Error: variable linkmon_period has not been set"
    error $result $errorInfo
}
if {![info exists linkmon_addr_dst]} {
    set result "EEM Policy Error: variable linkmon_addr_dst has not been set"
    error $result $errorInfo
}
if {![info exists linkmon_addr_src]} {
    set result "EEM Policy Error: variable linkmon_addr_src has not been set"
    error $result $errorInfo
}
if {![info exists linkmon_int]} {
    set result "EEM Policy Error: variable linkmon_int has not been set"
    error $result $errorInfo
}

# namespace imports
namespace import ::cisco::eem::*
namespace import ::cisco::lib::*

set numFail 0
get getNumFail [ appl_reqinfo key "failures" ]
if { [ lindex $getNumFail 0 ] == "data" } {
  set numFail [ lindex $getNumFail 1 ]
}

# save exact execution time for command
#set time_now [clock seconds]
set _status_file "disk0:packet_loss_exists"

if {![file exists $_status_file]} {

    # issue the cli command 
    if [catch {cli_open} result] {
        error $result $errorInfo
    } else {
        array set cli1 $result
    }

    # execute command
    if [catch {cli_exec $cli1(fd) "en"} result] {
        error $result $errorInfo
    }
    if [catch {cli_exec $cli1(fd) "term len 0"} result] {
        error $result $errorInfo
    }
    if [catch {cli_exec $cli1(fd) "ping $linkmon_addr_dst source $linkmon_addr_src size 1325 repeat 10"} result] {
        error $result $errorInfo
    }
    set cmd_output $result
    set routername [info hostname]
    if {[string match "" $routername]} {
        error "Host name is not configured"
    }

    regexp {(Success rate is .*[0-9] percent)} $cmd_output ping_result
    set success_rate [lindex $ping_result 3]
    if {$success_rate < 85} {
	incr numFail
	action_syslog priority info msg "linkmon.tcl: ping success rate was only $success_rate"
    } else {
	set numFail 0
    }
    appl_setinfo key "failures" data $numFail
    
    if {$numFail > 1} {
	action_syslog priority info msg "linkmon.tcl: ping failed more than twice in a row.. shutting interface $linkmon_int down"

        set myfileid [open $_status_file w+]
        foreach outs $cmd_output {
            puts $myfileid $outs
        }
        close $myfileid

        if [catch {cli_exec $cli1(fd) "config t"} result] {
            error $result $errorInfo
        }
        if [catch {cli_exec $cli1(fd) "interface $linkmon_int"} result] {
            error $result $errorInfo
        }
        if [catch {cli_exec $cli1(fd) "shut"} result] {
            error $result $errorInfo
        }
        if [catch {cli_exec $cli1(fd) "end"} result] {
            error $result $errorInfo
        }

        set _email_server "mail-out.nydc.fxcorp.prv"
        set _email_from "[email protected]"
        set _email_to "[email protected]"
        set _email_cc ""
        set _email_template "disk0:linkmon.tm"

        if [catch {smtp_subst $_email_template} result] {
            error $result $errorInfo
        }
        if [catch {smtp_send_email $result} result] {
            error $result $errorInfo
        }
    }

    if [catch {cli_close $cli1(fd) $cli1(tty_id)} result] {
        error $result $errorInfo
    }
}