Network Automation Nerds: PExpect Module

Saturday, November 24, 2012

PExpect Module

Ever since I started this blog I have this post in draft mode. It seems like a no brainer that PExpect goes hand-in-hand with network engineering using Python. Until network vendors starts to implement real APIs, we have to use an interactive program to ssh/telnet to the device, do some commands, screen scrap, and exit. This was the case when I started in the field a number of years ago, and this is the case now. It is kind of depressing to think that we have not made any significant progress all these years, actually. We are starting to see changes, but it will be a number of years before we see a wide adaptation.

So back to the original topic, since I have been meaning to write this blog, why the delay? There are two reasons:

1. The documentation and example of the pexpect module is excellent, http://www.noah.org/wiki/pexpect. I wish the examples can be directly posted on the web instead of looking thru the example subfolder, but that is just a small complain. The functions that is mostly used are on the site.

2. I will be a hypocrite if I say I am a complete believer in using this module 100% of the time. At times, such as when hoping thru a Cisco terminal server to access a device thru console, it just became too problematic that rather than debug, I just go with Tcl Explect. It is easy enough to write a small Expect script and use a Python wrapper with subprocess to execute it, much like my post on Expect, http://blog.pythonicneteng.com/2012/09/tcl-expect-with-python-part-1.html.

However, it is still a module that is very useful. Always nice to keep everything in Python so you dont need to go thru the mind-shift of another language.

Here is an example with pexpect that I wrote with the same objective as the Expect script that I posted, http://blog.pythonicneteng.com/2012/09/tcl-expect-with-python-part-1.html. Basically this is what it does:

1. Telnet to AT&T, Comcast, and University of Oregon route server.

2. Execute 'show ip route', and 'show ip bgp ' on the Bing.com IP.

Here is the list of route servers in a text file format:

$cat route-servers

route-server.ip.att.net

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

route-views.oregon-ix.net

$

Here is the list of commands in a text file format:

$cat commands.txt

show ip route 131.253.13.32

show ip bgp 131.253.13.32

$

Here is the script itself:

note. these are public route servers, sometimes you will get connection refused if all the vty lines are busy. They are also subject to change with no advance notice. Feel free to try out another route-server from www.traceroute.org.

[update 11/24, took out router = routeServer[0] that was a left over during testing, as a friend correctly pointed out]

$cat routeServ_pexpect.py
#!/usr/bin/env python
import sys,pexpect
# query file for all route servers and put into a list
routerFile = open('route-servers', 'r')
routeServers = [i for i in routerFile] #look up list comprehension is not clear
# query file for all commands and put into a list
commandFile = open('commands.txt', 'r')
commands = [i for i in commandFile]

# Starts the loop
for router in routeServers:
child = pexpect.spawn ('telnet', [router.strip()]) #option needs to be a list
child.logfile = sys.stdout #display progress on screen
child.expect ('Username:')
child.sendline('rviews')
for command in commands:
child.expect(['route-server', 'route-views']) #different options on prompt
child.sendline(command)
child.expect(['route-server', 'route-views'])

$

Here is the output:

$./routeServ_pexpect.py
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
rviews
route-server>show ip route 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 4w1d ago
Routing Descriptor Blocks:
* 12.123.1.236, from 12.123.1.236, 4w1d ago
Route metric is 0, traffic share count is 1
AS Hops 3
Route tag 7018
route-server>
route-server>show ip bgp 131.253.13.32
show ip bgp 131.253.13.32
BGP routing table entry for 131.253.12.0/22, version 711761
Paths: (18 available, best #13, table Default-IP-Routing-Table)
Not advertised to any peer
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)
12.123.21.243 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)
12.123.139.124 from 12.123.139.124 (12.123.139.124)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:34011
7018 8075 8075, (received & used)
12.123.33.249 from 12.123.33.249 (12.123.33.249)
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

route-server>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: rviews
Kerberos: No default realm defined for Kerberos!
rviews
route-server.newyork.ny.ibone>show ip route 131.253.13.32
show ip route 131.253.13.32
Command authorization failed.
route-server.newyork.ny.ibone>
route-server.newyork.ny.ibone>show ip bgp 131.253.13.32
show ip bgp 131.253.13.32
BGP routing table entry for 131.253.12.0/22, version 1517562788
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 68.86.80.10 (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)
68.86.1.38 (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)
68.86.1.41 (metric 73815) from 68.86.80.13 (68.86.1.13)
Origin IGP, metric 0, localpref 300, valid, internal
Community: 7922:41 7922:3020
Originator: 68.86.1.41, Cluster list: 68.86.1.13
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

route-server.newyork.ny.ibone>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
rviews
route-views>show ip route 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 100
Tag 8075, type external
Last update from 207.46.32.34 3d07h ago
Routing Descriptor Blocks:
* 207.46.32.34, from 207.46.32.34, 3d07h ago
Route metric is 100, traffic share count is 1
AS Hops 2
Route tag 8075
route-views>
route-views>show ip bgp 131.253.13.32
show ip bgp 131.253.13.32
BGP routing table entry for 131.253.12.0/22, version 218212
Paths: (33 available, best #7, table Default-IP-Routing-Table)
Not advertised to any peer
852 8075 8075
154.11.11.113 from 154.11.11.113 (154.11.11.113)
Origin IGP, metric 0, localpref 100, valid, external
Community: 852:180
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
4436 8075 8075
69.31.111.244 from 69.31.111.244 (69.31.111.244)
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 3549:200 3549:666 4436:21216 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

route-views>$

$