> For the complete documentation index, see [llms.txt](https://fashaun.gitbook.io/gw-feature/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://fashaun.gitbook.io/gw-feature/tcpdump.md).

# tcpdump

Read pcap file

```
$(tcpdump -r $file_name.pcap)
```

Capture in ASCII

```
$(tcpdump -A)
```

filter dhcp packet and write (-w) to file

```
$(tcpdump -i $interface_name -s 0 port 67 or port 68 -w "$file_name.pcap")
```

filter arp or other protocols (fddi, tr, wlan, ip, ip6, arp, rarp, decnet, tcp and udp)

```
$(tcpdump -i $interface_name arp)
```

filter destination

```
$(tcpdump -i $interface_name dst $ip_addr)
```

filter radius

```
#Check port number by /etc/services
$(tcpdump -i $interface_name port 1812 or port 1813 or port 3799)
```

Get radius attribute (Attr will be stripped in packet )

```
$(tcpdump -i $interface_name -s 0 port 1812 or port 1813 or port 3799)
```

Get VLAM ID

```
$(tcpdump -n -i $interface_name host $host_ip -e)
```

Display Captured Packets in HEX and ASCII

```
$(tcpdump -XX -i $interface)
```

\##Ping

Ping continueously

$(ping -t $ip -I $interface)