====== Finding IP addresses ======

Let's assume you must work in a network but they forgot to tell you the ip address range.


===== Passive sniffing =====

  * Simply use tcpdump, wireshark or any sniffer that displays the IP addresses of existing packets.

  * Eg:

  # tcpdump -nnei eth1
  13:46:05.577596 00:1a:73:3f:7a:9d > 00:03:6f:e1:5b:21, ethertype IPv4 (0x0800), length 74: 192.168.0.194.33387 > 80.58.32.97.53:  5597+ A? www.google.com. (32)
  13:46:05.676650 00:03:6f:e1:5b:21 > 00:1a:73:3f:7a:9d, ethertype IPv4 (0x0800), length 142: 80.58.32.97.53 > 192.168.0.1 94.33387:  5597 4/0/0 ...
In this example, ''192.168.0.194'' is a host in the network, and ''00:03:6f:e1:5b:21'' is the mac address of the gateway. We don't know the ip address of the gateway yet, that would probably require waiting for an arp packet, or try guess it, or active scan.


===== DHCP discovery =====

  * If DHCP is enabled on the network, use a dhcp client or a fast discovery tool like [[http://tv.latinsud.com/dhd/|DHD]].

  * Eg:
<code>
# dhd
Sniffing on any
Injecting on eth1 (00:0b:16:a1:b2:c3)

 #0:
        SERVER-MAC: 00:03:6f:e1:5b:21
               IP: 192.168.0.1
        CLIENT-MAC: 00:0b:16:a1:b2:c3
               IP: 192.168.0.195
               MASK: 255.255.255.0
        GW: 192.168.0.1
        DNS: 192.168.0.1

 >> "0  "0  "0  "0
</code>
In this example, ''192.168.0.1'' with mac address ''00:03:6f:e1:5b:21'' is the gateway.

===== Active scan =====

  * Use a fast ARP scanner like [[http://nixgeneration.com/~jaime/netdiscover/|netdiscover]], or a multipurpose one like nmap, ettercap, etc.

  * Eg:

<code>
  # netdiscover -i eth1
  Currently scanning: 192.168.1.0/16   |   Our Mac is: 00:0b:16:a1:b2:c3

  2 Captured ARP Req/Rep packets, from 2 hosts.   Total size: 102
  _____________________________________________________________________________
   IP            At MAC Address      Count  Len   MAC Vendor
  -----------------------------------------------------------------------------
  192.168.0.1     00:03:6f:e1:5b:21    01    042   Telsey SPA
  192.168.0.194   00:1a:73:3f:7a:9d    01    060   Unknown vendor
</code>
In this example, there are 2 hosts from which ''192.168.0.1'' with mac address ''00:03:6f:e1:5b:21'' seems to be the gateway.