# IP Forwarding ## Info Detects whether the remote device has ip forwarding or "Internet connection sharing" enabled, by sending an ICMP echo request to a given target using the scanned host as default gateway. ### Check status ``` # sysctl net.ipv4.ip_forward net.ipv4.ip_forward = 1 ``` ### enable ip forwarding ``` sysctl -w net.ipv4.ip_forward=1 ``` ### How to identify systems on the local LAN Use your favourite ARP scanning to identify systems on the local LAN. Save the output (I use to arp.txt in the example below). * For IPv4 * `arp-scan -l` * `arp-scan -l` ``` arp-scan -l | tee arp_scan_macs.txt Interface: eth0, datalink type: EN10MB (Ethernet) Starting arp-scan 1.6 with 256 hosts (http://www.nta-monitor.com/tools/arp-scan/) 10.0.0.100 00:13:72:09:ad:76 Dell Inc. 10.0.0.200 00:90:27:43:c0:57 INTEL CORPORATION 10.0.0.254 00:08:74:c0:40:ce Dell Computer Corp. 3 packets received by filter, 0 packets dropped by kernel Ending arp-scan 1.6: 256 hosts scanned in 2.099 seconds (121.96 hosts/sec). 3 responded ``` * `arp` * `arp -a` ``` arp -a | tee arp_macs.txt (10.10.2.1) at 1f:2e:39:d7:2f:04 [ether] on eth0 (10.10.2.3) at 1f:23:39:d8:2e:44 [ether] on eth0 ``` * For IPv6 * `ip` `ip -6 neighbor` ``` fe80::ca21:aabe:fdc6:d7c1 dev eth0 lladdr f9:42:64:d6:0a:d5 router STALE ``` ## Nmap Usage `sudo nmap -sn --script ip-forwarding --script-args='target=www.example.com'` Example: ``` root@Kali:~# nmap -sn 192.168.0.30 --script ip-forwarding --script-args='target=192.168.73.130' Starting Nmap 7.80 (https://nmap.org) at 2020-01-23 14:20 GMT Nmap scan report for 192.168.0.30 Host is up (0.00097s latency). MAC Address: 00:0C:29:B2:A4:BD (VMware) Host script results: | ip-forwarding: |_ The host has ip forwarding enabled, tried ping against (192.168.73.130) ``` ## Nessus Look for 'IP Forwarding Enabled' ## Gateway Finder Gateway-finder is a scapy script that will help you determine which of the systems on the local LAN has IP forwarding enabled and which can reach the Internet. ### Usage Collet mac address of the hosts you want to check `arp-scan -l | tee arp.txt` Step 2: Run gateway-finder on the list of local systems Gateway-finder needs two bits of input from you: * The MAC addresses of the potential gateways * The IP address of a system on the Internet (I use a google.com address in the example below): If arp.txt also contains an IP of each system on the same line as the MAC, you'll get much nicer output. If you need to use a different network interfaces, use the -I option. `python gateway-finder.py -f arp.txt -i 209.85.227.99` ``` # python gateway-finder.py -f arp.txt -i 209.85.227.99 gateway-finder v1.0 http://pentestmonkey.net/tools/gateway-finder [+] Using interface eth0 (-I to change) [+] Found 3 MAC addresses in arp.txt [+] 00:13:72:09:AD:76 [10.0.0.100] appears to route ICMP Ping packets to 209.85.227.99. Received ICMP TTL Exceeded in transit response. [+] 00:13:72:09:AD:76 [10.0.0.100] appears to route TCP packets 209.85.227.99:80. Received ICMP TTL Exceeded in transit response. [+] We can ping 209.85.227.99 via 00:13:72:09:AD:76 [10.0.0.100] [+] We can reach TCP port 80 on 209.85.227.99 via 00:13:72:09:AD:76 [10.0.0.100] [+] Done ``` ## Gateway Finder imp Link: Usage: * `sudo python3 gateway-finder-imp.py` * `-h` - help * `-M ` - use file with next-hop MACs * `-m ` - use selected next-hop MAC * `-d ` - use selected destination IPs * `-D ` - use file with selected destination IPs * `-i ` - use selected network interface * `-p ... ` - use ports * `--v` - verbose mode * `--vv` - maximum verbosity * examples * `gateway-finder-imp.py -d 8.8.8.8 -m de:ad:be:af:de:ad -i enp0s31f6` use selected next-hop MAC and selected destination IP * `gateway-finder-imp.py -D dst_hosts.txt -M next_hop_macs.txt -i wlp3s0` - use selected next-hop MAC and file with selected destination IPs * `gateway-finder-imp.py -d 8.8.8.8 -M next_hop_macs.txt -i eth0` - use file with next-hop MACs and file with selected destination IPs * `gateway-finder-imp.py -D file_with_dst_IPs.txt -M file_with_nex_hop_MACs.txt -i eth1 -p 22 443 80 8080 23` * `gateway-finder-imp.py -d 2a00:1450:4010:c05::64 -M mac_with_ipv6_0.txt -i wlp3s0 -p 443 80 -6 --vTries to find a layer-3 gateway to the Internet. Attempts to reach an IP` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://infra.newerasec.com/infrastructure-testing/gaining-access/ip-forwarding.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.