Question

I currently have an implementation using the pexpect python module, which interacts with Juniper, Cisco routers. It spawns a child application and runs command like ‘show version’ and logs the output.

I am looking for a better way to carry out this process, since if something changes on the switch end (a space or a colon in the prompt after an OS upgrade), then the program will not work. I think Juniper has an API to carry out such operations, but I don’t think Cisco has one. I also need to extend this to other switches like HP etc.

Is there a generalized way I can approach this?

I also don’t mind writing different code for different devices if required, if a more standard approach than pexpect exists.

Thanks

Answer 1

Using some version of expect is the accepted way of doing this. There’s already a mature piece of OSS scripts for doing terminal interaction with most networking devices form most vendors. The same problem exists, but a lot more eyeballs are looking at it and updating things when vendors change prompts.

Check out RANCID.

Here’s a quick example of a script I wrote based on RANCID to harvest ACL hit counts on ASAs:

#!/usr/bin/perl

use strict;
use Getopt::Std;

my $usage = "Usage: gethitcnt.pl -c configfile -o outputdir\n\n";
my %opts;

getopts('hc:o:', \%opts);

my $login = sprintf "~%s\/bin\/clogin.in", $ENV{'HOME'};
my $loginrc = sprintf "~%s\/.cloginrc", $ENV{'HOME'};
my $cmdfile = sprintf "~%s\/cmd", $ENV('HOME');
my $date = getdate;
my ($config,$outdir);

unless (-e $login) {
 die "Cannot find $login\n\n";
}

unless (-e $loginrc) {
 die "Cannot find $loginrc\n\n";
}

if ($opts{h} or !$opts{c}) {
 die $usage;
}

if ($opts{o}) {
 $outdir = $opts{o};
} else {
 $outdir = $ENV{'PWD'};
}

if (-e $opts{c}) {
 $config = getconfig($opts{c});
} else {
 die "Cannot open config file $opts{c}\n\n";
}

foreach my $firewall (keys %$config) {
 foreach my $acl (@{$config->{$firewall}}) {
  open (CMD,>$cmdfile);
  print CMD "show access-list $acl\n";
  print CMD "clear access-list $acl counters\n";
  close (CMD);
  my $command = ($login,"-x",$cmdfile,$firewall)
  open (TMP,"$command |");
  my $outfile = sprintf "%s\/%s-%s-%s.txt", $outdir, $firewall, $acl, $date;
  open (OUTFILE,>$outfile);
  foreach my $line (<TMP>) {
   if ($line =~ /\s*(access-list.*\(hitcnt=\d+\))/) {
    print OUTFILE "$1\n";
   }
  }
  system ("rm",$cmdfile);
 }
}

sub getconfig {
 my $configfile = shift;
 open(CONFIG,$configfile);
 my $out;
 foreach (<CONFIG>) {
  chomp;
  my @$elements = split(/,/);
  my $host = shift(@$elements);
  $out->{$host} = $elements;
 }
 close(CONFIG);
 return($out);
}

sub getdate {
 my @time = localtime;
 my @abbr = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec );
 my $month = $abbr[$time[4]];
 my $out = sprintf "%s-%d", $month, $time[3];
 return($out);
}