Tcl Expect with Python - part 1

Note. highly recommended the go-to book on the subject: Exploring Expect: A Tcl-based Toolkit for Automating Interactive Programs (Nutshell Handbooks)

I have a love-hate relationship with Expect. I love what it can do for automating interactive sessions with routers, but I hate the unpredictability associated with interactive sessions. It seems that we will make a script, tweak it enough to make it work, just to do it all over again in a few months. It is just a fragile process, whenever there is a new hardware, new terminal server, or even a new OS, we will hit something that require some more fine tuning. We are much better off with known API, autoprovioning via DHCP/TFTP, or other tools for what we use Expect for today.

But until the day when all the network vendor can agree on a given set of API and hooks (if ever), Expect is still a must have in any network engineer's tool bag. It will save you time and keep you sane. 

Note that this is a post for the regular Expect based on Tcl, more on PExpect module in later post.

For those who have not heard of Expect, or want a refresher, here are a few documentation link. 

References:  

http://expect.sourceforge.net/

http://wiki.tcl.tk/201 (updated link on 12/29/2016)

http://www.nist.gov/el/msid/expect.cfm

Here is a useful link for special ASCII Characters, when you want to send those Ctrl-C, Ctrl-X, space, etc:

http://www.bbdsoft.com/ascii.html
[Update 12/29/2016, this link expired (thank you Kirk for pointing it out). Still searching for a good link]

At the heart of the game, Expect is about 1. spawing a child process, 2. look for certain words in the stream via expect, 3. send something over. 

So say I want to telnet to a bunch of Public route-servers and look at how bing.com's IP looks from the route server. I find out that bing.com resolves to 131.253.13.32 from where I am at. 

Non-authoritative answer:

Name: bing.com

Address: 131.253.13.32

From Route Server (http://traceroute.org/#Route%20Servers) I can find a list of public route servers that  I can telnet to. 

1. Using AT&T's route server as a first example, I am going to write a simple script that telnets to the box and displays the bgp information: 

#!/usr/bin/expect
set timout 5
# Spawns a child process that telnets to AT&T public route server
spawn telnet route-server.ip.att.net
# The expect command waits until the child process returns "Username:"
# then sends 'reviews' and a return key
expect "Username:" {send "rviews\r"};
# The process then sits and wait for the route-server> prompt
# Then sends the command for route 131.253.13.32 (one of the ip for bing.com)
expect "route-server>" {send "show ip bgp 131.253.13.32\r"};
# The output is longer than 1 page, so it sendds the ASCII key for space twice
send "\032\032"
# Looks for the same prompt, then types 'exit'
expect "route-server>" {send exit\r};

2. The first script can now be cron'd and give me the information that I wanted. But what if I want to telnet to a bunch of route-server, not just AT&T? Here is a modified version that uses the first argument as the telnet target: 

#!/usr/bin/expect
set routeServ [lindex $argv 0]
set timout 20
spawn telnet $routeServ
expect "Username:" {send "rviews\r"};
expect {
  -re "route.*" {send "show ip bgp 131.253.13.32\r"};
}
send "\032\032"
expect {
  -re "route.*" {send exit\r};
}

Notice that the script also now uses -re to indicate the expected string back will be regular expression. This is because some of the route server prompt are 'route-server>' as in the case of AT&T and Comcast, while some are 'route-view>', as in the case of Oregon Route-View servers. 

Now that is just another script that I can use Python to tie in, reading from a list of route-servers:

$cat route-servers 

route-server.ip.att.net 

route-server.newyork.ny.ibone.comcast.net

route-views.oregon-ix.net

$

Here is the Python script: 

#!/usr/bin/env python
import subprocess
f = open("route-servers", "r")
for i in f.readlines():
subprocess.check_call(["./routeServ_2.exp", i.strip()])

3. Now we are getting somewhere, but there is another problem: the command is embedded into the Expect script itself. So if I want to run more commands, I need to modify the expect script itself. That is not very flexible. I will make one more modification to the Expect script itself so that it reads all the command from another text file: 

$cat commands.txt 

show ip route 131.253.13.32

show ip bgp 131.253.13.32

Here is the new version of the Expect script. Note that 'timeout -1' disables the default timeout of 10 seconds, as some of the route-servers are pretty slow. 

#!/usr/bin/expect
set routeServ [lindex $argv 0]
# disable the timeout value in the next line
# since some of the route-servers are really slow
set timout -1

spawn telnet $routeServ
expect "Username:" {send "rviews\r"};
expect {
  -re "route-.*" {send \r}
}
#process the command file
#this can be more elegant, but this is more clear
set file [open "commands.txt" r]
set file_data [read $file]
set command [split $file_data "\n"]
foreach line $command {
  puts $line
  expect {
    -re "route-.*" {send $line\r}
    continue
  }
  send "\032\032\032"
  sleep 2
}

Now I will tie it in with Python, there is no change to the Python script except that it calls the new Expect script. By using Python, I can leverage the getpass, subprocess, sys, and other standard libraries and not have to deal with Tcl or Expect. 

#!/usr/bin/env python
import subprocess
f = open("route-servers", "r")
for i in f.readlines():
    subprocess.check_call(["./routeServ_3.exp", i.strip()])

4. Here is the output of the result as it shows on the screen (Comcast route server does not allow for 'show ip route x.x.x.x', boo):

$./routeServ_3.py 

spawn telnet route-server.ip.att.net

Trying 12.0.1.28...

Connected to route-server.cbbtier3.att.net.

Escape character is '^]'.

-------------- route-server.ip.att.net ---------------

---------  AT&T IP Services Route Monitor  -----------

The information available through route-server.ip.att.net is offered

by AT&T's Internet engineering organization to the Internet community.

This router maintains eBGP peerings with customer-facing routers

throughout the AT&T IP Services Backbone:

IPv4:

 12.123.21.243  Atlanta   12.123.133.124 Austin    12.123.41.250  Cambridge

 12.123.5.240   Chicago   12.123.17.244  Dallas    12.123.139.124 Detroit

 12.123.37.250  Denver    12.123.134.124 Houston   12.123.29.249  LA

 12.123.1.236   New York  12.123.33.249  Orlando   12.123.137.124 Philly

 12.123.142.124 Phoenix   12.123.145.124 SanDiego  12.123.13.241  SanFran

 12.123.25.245  St.Louis  12.123.45.252  Seattle   12.123.9.241   WashDC

IPv6:

 2001:1890:FF:FFFF:12:122:124:12   Atlanta

 2001:1890:FF:FFFF:12:122:127:66   Chicago

 2001:1890:FF:FFFF:12:122:124:138  Dallas

 2001:1890:FF:FFFF:12:122:120:7    Fort Lauderdale

 2001:1890:FF:FFFF:12:122:125:6    Los Angeles

 2001:1890:FF:FFFF:12:122:125:44   New York

 2001:1890:FF:FFFF:12:122:125:106  Philadelphia

 2001:1890:FF:FFFF:12:122:125:132  Phoenix

 2001:1890:FF:FFFF:12:122:126:232  San Francisco

 2001:1890:FF:FFFF:12:122:125:224  Seattle

 2001:1890:FF:FFFF:12:122:126:9    St. Louis

 2001:1890:FF:FFFF:12:122:126:64   Washington

*** Please Note:

Ping and traceroute delay figures measured here are unreliable, due to the

high CPU load experienced when complicated "show" commands are running.

For questions about this route-server, send email to: jayb@att.com

*** Log in with username "rviews", no password required ***

User Access Verification

Username: Kerberos: No default realm defined for Kerberos!

rviews

route-server>show ip route 131.253.13.32

route-server>show ip bgp 131.253.13.32

show ip route 131.253.13.32

Routing entry for 131.253.12.0/22

  Known via "bgp 65000", distance 20, metric 0

  Tag 7018, type external

  Last update from 12.123.1.236 22:16:35 ago

  Routing Descriptor Blocks:

  * 12.123.1.236, from 12.123.1.236, 22:16:35 ago

      Route metric is 0, traffic share count is 1

      AS Hops 3

      Route tag 7018

route-server>

show ip bgp 131.253.13.32

BGP routing table entry for 131.253.12.0/22, version 36560492

Paths: (18 available, best #2, table Default-IP-Routing-Table)

  Not advertised to any peer

  7018 8075 8075, (received & used)

    12.123.13.241 from 12.123.13.241 (12.123.13.241)

      Origin IGP, localpref 100, valid, external

      Community: 7018:2500 7018:32113

  7018 8075 8075, (received & used)

    12.123.1.236 from 12.123.1.236 (12.123.1.236)

      Origin IGP, localpref 100, valid, external, best

      Community: 7018:2500 7018:38001

  7018 8075 8075, (received & used)

    12.123.142.124 from 12.123.142.124 (12.123.142.124)

      Origin IGP, localpref 100, valid, external

      Community: 7018:2500 7018:33051

  7018 8075 8075, (received & used)

    12.123.133.124 from 12.123.133.124 (12.123.133.124)

      Origin IGP, localpref 100, valid, external

      Community: 7018:2500 7018:36244

  7018 8075 8075, (received & used)

    12.123.17.244 from 12.123.17.244 (12.123.17.244)

      Origin IGP, localpref 100, valid, external

      Community: 7018:2500 7018:36244

  7018 8075 8075, (received & used)

    12.123.21.243 from 12.123.21.243 (12.123.21.243)

      Origin IGP, localpref 100, valid, external

      Community: 7018:2500 7018:36244

  7018 8075 8075, (received & used)

    12.123.137.124 from 12.123.137.124 (12.123.137.124)

      Origin IGP, localpref 100, valid, external

      Community: 7018:2500 7018:38001

  7018 8075 8075, (received & used)

    12.123.41.250 from 12.123.41.250 (12.123.41.250)

      Origin IGP, localpref 100, valid, external

      Community: 7018:2500 7018:38001

  7018 8075 8075, (received & used)

    12.123.139.124 from 12.123.139.124 (12.123.139.124)

          

route-server>spawn telnet route-server.newyork.ny.ibone.comcast.net

Trying 66.208.229.1...

Connected to route-server.newyork.ny.ibone.comcast.net.

Escape character is '^]'.

********************************************************************************

                       Comcast NETO Route Server

        This route server is provided by Comcast National Engineering &

Technical Operations to provide visibility into the Internet routing table

from the perspective of Comcast's network.  This server has BGP peerings to

the following routers and the Internet routing table view from each device:

68.86.80.0 - Ashburn, VA

68.86.80.2 - New York, NY

68.86.80.5 - Chicago, IL

68.86.80.6 - Chicago, IL 2

68.86.80.7 - Denver, CO

68.86.80.10 - San Jose, CA

68.86.80.11 - Los Angeles, CA

68.86.80.12 - Atlanta, GA

68.86.80.13 - Dallas, TX

          

Note: Due to high CPU utilization on this device, ping and traceroute results

may be unreliable.  This route server should not be used to measure network

performance as a result.

Login with username: rviews

Location:   New York City

Network:  Comcast Route Server

********************************************************************************

User Access Verification

Username: Kerberos: No default realm defined for Kerberos!

rviews

route-server.newyork.ny.ibone>show ip route 131.253.13.32

route-server.newyork.ny.ibone>show ip bgp 131.253.13.32

show ip route 131.253.13.32

Command authorization failed.

route-server.newyork.ny.ibone>

show ip bgp 131.253.13.32

BGP routing table entry for 131.253.12.0/22, version 1378467282

Paths: (8 available, best #8, table Default-IP-Routing-Table)

  Advertised to update-groups:

     2         

  8075 8075, (received & used)

    68.86.1.38 (metric 81950) from 68.86.80.11 (68.86.1.11)

      Origin IGP, metric 0, localpref 300, valid, internal

      Community: 7922:38 7922:3020

      Originator: 68.86.1.38, Cluster list: 68.86.1.11, 68.86.1.10

  8075 8075, (received & used)

    68.86.1.75 (metric 74391) from 68.86.80.13 (68.86.1.13)

      Origin IGP, metric 0, localpref 300, valid, internal

      Community: 7922:75 7922:3020

      Originator: 68.86.1.75, Cluster list: 68.86.1.13, 68.86.1.7

  8075 8075, (received & used)

    68.86.1.40 (metric 69750) from 68.86.80.12 (68.86.1.12)

      Origin IGP, metric 0, localpref 300, valid, internal

      Community: 7922:40 7922:3020

      Originator: 68.86.1.40, Cluster list: 68.86.1.12

  8075 8075, (received & used)

    68.86.1.42 (metric 66845) from 68.86.80.0 (68.86.1.0)

      Origin IGP, metric 0, localpref 300, valid, internal

      Community: 7922:42 7922:3020

      Originator: 68.86.1.42, Cluster list: 68.86.1.0

  8075 8075, (received & used)

    68.86.1.38 (metric 81950) from 68.86.80.10 (68.86.1.10)

      Origin IGP, metric 0, localpref 300, valid, internal

      Community: 7922:38 7922:3020

      Originator: 68.86.1.38, Cluster list: 68.86.1.10

  8075 8075, (received & used)

    68.86.1.43 (metric 69675) from 68.86.80.6 (68.86.1.6)

      Origin IGP, metric 0, localpref 300, valid, internal

      Community: 7922:43 7922:3020

      Originator: 68.86.1.43, Cluster list: 68.86.1.6

  8075 8075, (received & used)

    68.86.1.75 (metric 74391) from 68.86.80.7 (68.86.1.7)

      Origin IGP, metric 0, localpref 300, valid, internal

          

route-server.newyork.ny.ibone>spawn telnet route-views.oregon-ix.net

Trying 128.223.51.103...

Connected to route-views.oregon-ix.net.

Escape character is '^]'.

 **********************************************************************

                    Oregon Exchange BGP Route Viewer

          route-views.oregon-ix.net / route-views.routeviews.org

 route views data is archived on http://archive.routeviews.org

 This hardware is part of a grant from Cisco Systems.

 Please contact help@routeviews.org if you have questions or

 comments about this service, its use, or if you might be able to

 contribute your view.

 This router has views of the full routing tables from several ASes.

 The list of ASes is documented under "Current Participants" on

 http://www.routeviews.org/.

                          **************

 route-views.routeviews.org is now using AAA for logins.  Login with

 username "rviews".  See http://routeviews.org/aaa.html

 **********************************************************************

User Access Verification

Username: rviews

route-views>show ip route 131.253.13.32

route-views>show ip bgp 131.253.13.32

show ip route 131.253.13.32

Routing entry for 131.253.12.0/22

  Known via "bgp 6447", distance 20, metric 0

  Tag 8075, type external

  Last update from 207.46.32.34 7w0d ago

  Routing Descriptor Blocks:

  * 207.46.32.34, from 207.46.32.34, 7w0d ago

      Route metric is 0, traffic share count is 1

      AS Hops 1

      Route tag 8075

route-views>

show ip bgp 131.253.13.32

BGP routing table entry for 131.253.12.0/22, version 215869

Paths: (33 available, best #20, table Default-IP-Routing-Table)

  Not advertised to any peer

  3277 3267 8075 8075

    194.85.102.33 from 194.85.102.33 (194.85.4.4)

      Origin IGP, localpref 100, valid, external

      Community: 3277:3267 3277:65100 3277:65320 3277:65326 3277:65330

  3333 3356 8075 8075

    193.0.0.56 from 193.0.0.56 (193.0.0.56)

      Origin IGP, localpref 100, valid, external

  3561 3356 8075 8075

    206.24.210.102 from 206.24.210.102 (206.24.210.102)

      Origin IGP, localpref 100, valid, external

  3356 8075 8075

    4.69.184.193 from 4.69.184.193 (4.69.184.193)

      Origin IGP, metric 0, localpref 100, valid, external

      Community: 209:80 209:888 701:30 703:30 1120:2 1299:2869 1299:5509 1299:5583 2914:470 3356:3 3356:22 3356:100 3356:123 3356:575 3356:2012 3549:200 3549:666 4657:905 5511:1550 6453:80 6762:20008 7018:80 7473:22009 7473:23009 10026:11010 10026:11020 10026:11030 10026:11040 10026:11050 10026:11060 10026:11070 10026:11080 10026:11090 10026:11100 25160:209 25160:1239 65009:7018

  2914 3356 8075 8075

    129.250.0.11 from 129.250.0.11 (129.250.0.12)

      Origin IGP, metric 6, localpref 100, valid, external

      Community: 2914:420 2914:1008 2914:2000 2914:3000 65504:3356

  19214 12989 8075 8075

    208.74.64.40 from 208.74.64.40 (208.74.64.40)

      Origin IGP, localpref 100, valid, external

  101 101 8075 8075

    209.124.176.223 from 209.124.176.223 (209.124.176.223)

      Origin IGP, localpref 100, valid, external

      Community: 101:20400 101:22200

      Extended Community: RT:101:22200

  6939 8075 8075

    216.218.252.164 from 216.218.252.164 (216.218.252.164)

      Origin IGP, localpref 100, valid, external

  1239 3356 8075 8075

    144.228.241.130 from 144.228.241.130 (144.228.241.130)

          

route-views>$