A simple example tracking down a routing path through a BGP/MPLS/LDP Junos network.

trace-route-ldp.rb

require 'highline/import'
require 'net/netconf/jnpr'

target = ARGV[0] || begin
  puts "You must specify a starting target device"
  exit 1
end
  
dst_route = ARGV[1] || begin
  puts "You need to specify a destination route"
  exit 1
end

my_username = ENV["USER"]
puts "login: #{my_username}"
my_password = ask("password: "){|a| a.echo = false}

module ScannerLDP
  
  def get_lldp_nei( ifd_name )      
    ifd_name.gsub!(/\.\d+/, '')    # drop the IFL    
    rsp = @rpc.command "show lldp neighbors interface #{ifd_name}"
    if_nei = rsp.xpath('lldp-neighbor-information')
    rmt_sysname = if_nei.xpath('lldp-remote-system-name').text
    rmt_ip = if_nei.xpath('lldp-remote-management-address').text
    { :rmtsys => rmt_sysname, :rmtip => rmt_ip }
  end
  
  def get_lacp_ifds( ae_name )
    ae_name.gsub!(/\.\d+/, '')    # drop the IFL
    rsp = @rpc.get_lacp_interface_information( :interface_name => ae_name )
    rsp.xpath('//lag-lacp-protocol/name').collect{|i| i.text}
  end

  def nh_proc( nh )    
    nh_table = nh.xpath('nh-table').text
    nh_mpls = nh.xpath('mpls-label').text
    
    rdat = {}
    rdat[:protocol] = nh.xpath('../protocol-name').text
    rdat[:nh] = nh.xpath('to').text
    rdat[:via] = nh.xpath('via').text
    rdat[:table] = nh_table unless nh_table.empty?
    rdat[:mpls] = nh_mpls unless nh_mpls.empty?

    rdat
  end
  
  def get_active_route( opts )
    rpc_args = {}
    rpc_args[:destination] = opts[:dest]
    rpc_args[:active_path] = true
    rpc_args[:table] = opts[:table] if opts[:table]
    
    as_txt = (opts[:as_txt]) ? { :format => 'text' } : nil
    
    rsp = @rpc.get_route_information( rpc_args, as_txt )
    
    if as_txt
      rsp.text
    else 
      nh = rsp.xpath('//nh[selected-next-hop]')[0] || rsp.xpath('//nh')[0]
      nh_proc( nh )
    end
  end
  
  def get_mpls_route( label )
    rsp = @rpc.get_route_information( :table => 'mpls', :label => label )
    nh = rsp.xpath('//nh')[0]    
    nh_proc( nh )
  end

  def get_next_rtr( nhop )
    ifd_name = nhop[:via]
    if ifd_name.match /ae\d/
      ifd_name = get_lacp_ifds( ifd_name )[0]
    end    
    lldp_nei = get_lldp_nei( ifd_name )
  end
  
end

def mpls_stack_proc( mpls_stack, mpls_txt_acts )
  mpls_txt_acts.scan(/(\w+)\s?(\d+)?,?/).each do |action|
    case action[0]
    when "Push"
      mpls_stack.unshift action[1]    
    when "Pop"
      mpls_stack.shift
    when "Swap"
      mpls_stack[0] = action[1]
    end 
  end  
  mpls_stack
end

login = { :username => my_username, :password => my_password }
login[:target] = target

mpls_stack = []
done = false

until done
  
  puts "\nLOGGING INTO: #{target} ..."
  
  dev = Netconf::SSH.new( login )
  dev.extend ScannerLDP
  dev.open  
  
  if mpls_stack.empty?
    nhop = dev.get_active_route( :table => 'wireless', :dest => dst_route )
  else
    nhop = dev.get_mpls_route( mpls_stack[0] )
  end

  if nhop[:mpls]
    mpls_stack_proc( mpls_stack, nhop[:mpls] )
  end
    
  if mpls_stack.empty?
    puts "MPLS stack is empty, we're at the end ..."
    nhop = dev.get_active_route( :table => nhop[:table], :dest => dst_route, :as_txt => true )    
    puts nhop
    puts "\nDONE!"
    done = true
  else   
    puts "MPLS stack is now: " + mpls_stack.join(",")    
    
    next_rtr = dev.get_next_rtr( nhop )
    login[:target] = next_rtr[:rmtip]
    target = next_rtr[:rmtsys]
  end
  
  dev.close
end

trace-route-ldp.txt

$ ruby trace-route-ldp.rb mx240-176 192.168.199.0
login: jschulman
password:

LOGGING INTO: mx240-176 ...
MPLS stack is now: 300896,18

LOGGING INTO: MX480-R244 ...
MPLS stack is now: 301088,18

LOGGING INTO: MX240-R178 ...
MPLS stack is now: 18

LOGGING INTO: MX240-R130-re0 ...
MPLS stack is empty, we're at the end ...


wireless.inet.0: 13 destinations, 26 routes (13 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

192.168.199.0/24   *[OSPF/10] 20:38:57, metric 2
                    > to 10.0.0.33 via xe-2/1/2.110

DONE!