Hiding Routing Path for the Traceroute Applications by Looping Traceroute Packets

How Traceroute Works?

There are several Traceroute Applications including tracert, traceroute etc..  each of them use different protocols although the method is the same.
ex : Tracert uses ICMP echo   while Traceroute uses UDP protocol.

so in this Lab i configured this Looping method only for tracing applications which use ICMP echo and UDP protocols.

the common method is Tracing application sends a packet or packets (= Probe count) to Destination IP by increasing its TTL value in the IP header step by step. each nod or layer 3 device normally decrease packet TTL when it got the packet. as soon as TTL is equal 0 router will send an ICMP time exceed error packet to the tracing application's nod.

Steps to Configure

1st Step

Create an ACL to filter Tracing Packets.. it can be filtered in several ways.
ex: by TTL value , protocols or source/destination ip..
but i use TTL value for filtering.


2nd Step

Create a Route-map and matches the ACL and define the Action
in this case action is route packet to the specific next-hop


3rd Step

Apply Route-map for an Interface



This Looping Method i used also called Policy based Route or PBR

Topology

Loop Occurs between R2 interface fa1/0 and R3 interface fa1/0

Configurations

R1 Configs...

 !  
 !  
 interface Loopback0  
  ip address 1.1.1.1 255.255.255.255  
 !  
 interface FastEthernet0/0  
  ip address 10.0.0.1 255.255.255.252  
  duplex full  
 !  
 interface FastEthernet1/0  
  ip address 192.168.1.1 255.255.255.0  
  duplex half  
 !  
 router eigrp 1  
  network 1.1.1.1 0.0.0.0  
  network 10.0.0.0 0.0.0.3  
  network 192.168.1.0  
  no auto-summary  
 !  

R2 Configs...

   
 !  
 !  
 interface Loopback0  
  ip address 2.2.2.2 255.255.255.255  
 !  
 interface FastEthernet0/0  
  mac-address 0000.2222.0000  
  ip address 10.0.0.5 255.255.255.252  
  duplex full  
  speed auto  
 !  
 interface FastEthernet0/1  
  mac-address 0000.2222.1111  
  ip address 10.0.0.2 255.255.255.252  
  ip policy route-map ICMP_MAP  
  duplex full  
  speed auto  
 !  
 interface FastEthernet1/0  
  mac-address 0000.2222.2222  
  ip address 10.0.0.13 255.255.255.252  
  ip policy route-map ICMP_MAP  
  duplex half  
 !  
 router eigrp 1  
  network 2.2.2.2 0.0.0.0  
  network 10.0.0.0 0.0.0.3  
  network 10.0.0.4 0.0.0.3  
  no auto-summary  
 !  
 ip access-list extended ROUND_ICMP  
  permit udp any any ttl lt 35  
  permit icmp any any traceroute  
  permit icmp any any ttl lt 35  
 !  
 logging alarm informational  
 !  
 !  
 !  
 route-map ICMP_MAP permit 5  
  match ip address ROUND_ICMP  
  set ip next-hop 10.0.0.14  
 !  
 !  

R3 Configs...

   
 !  
 interface Loopback0  
  ip address 3.3.3.3 255.255.255.255  
 !  
 interface FastEthernet0/0  
  mac-address 0000.3333.0000  
  ip address 10.0.0.10 255.255.255.252  
  ip policy route-map ICMP_MAP  
  duplex full  
  speed auto  
 !  
 interface FastEthernet0/1  
  mac-address 0000.3333.1111  
  ip address 10.0.0.6 255.255.255.252  
  duplex full  
  speed auto  
 !  
 interface FastEthernet1/0  
  mac-address 0000.3333.3333  
  ip address 10.0.0.14 255.255.255.252  
  ip policy route-map ICMP_MAP  
  duplex half  
 !  
 router eigrp 1  
  network 3.3.3.3 0.0.0.0  
  network 10.0.0.4 0.0.0.3  
  network 10.0.0.8 0.0.0.3  
  no auto-summary  
 !  
 !  
 ip access-list extended ROUND_ICMP  
  permit udp any any ttl lt 35  
  permit icmp any any traceroute  
  permit icmp any any ttl lt 35  
 !  
 logging alarm informational  
 !  
 !  
 !  
 route-map ICMP_MAP permit 5  
  match ip address ROUND_ICMP  
  set ip next-hop 10.0.0.13  
 !  
 !  

R4 Configs...

 !  
 interface Loopback0  
  ip address 4.4.4.4 255.255.255.255  
 !  
 interface FastEthernet0/0  
  ip address 10.0.0.9 255.255.255.252  
  duplex full  
 !  
 router eigrp 1  
  network 4.4.4.4 0.0.0.0  
  network 10.0.0.8 0.0.0.3  
  no auto-summary  
 !  

That's it... :)

Any trouble ?? Please comment.. Thank you