常见语法
过滤器支持的函数：
过滤器的语言还有下面几个函数：
upper(string－field)－把字符串转换成大写
lower(string－field)－把字符串转换成小写
upper((和lower((在处理大小写敏感的字符串比较时很有用。例如：
upper(ncp.nds_stream_name) contains "MACRO"
lower(mount.dump.hostname) =="angel"
协议字段类型
每个协议的字段都有规定的类型。这些类型是：
unsigned integer 无符号整数（8比特、16比特、24比特、32比特）
signed integer 有符号整数（8比特、16比特、24比特、32比特）
Boolean 布尔值
Ethernet address 以太网地址（6字节）
Byte array 字节数组
IPv4 address IPv4地址
IPv6 address IPv6地址
IPX network number IPX网络地址
Text string 文本串
Double-precision floating point number 双精度浮点值
三种进制表示方法：
frame.pkt_len>10
frame.pkt_len>012
frame.pkt_len>0xa
布尔值用1 0表示
以太网地址
eth.dst eq ff:ff:ff:ff:ff:ff
aim.data == 0.1.0.d
fddi.src == aa-aa-aa-aa-aa-aa
echo.data == 7a
ipv4和主机名
ip.dst eq www.mit.edu
ip.src == 192.168.1.1
示例：
获取from或to ip 111.111.111.111
host 172.18.5.4
获取from或to ip 段
net 192.168.0.0/24 or net 192.168.0.0 mask 255.255.255.0
from ip段
src net 192.168.0.0/24 or src net 192.168.0.0 mask 255.255.255.0
to ip地址段
dst net 192.168.0.0/24 or dst net 192.168.0.0 mask 255.255.255.0
指定port数据
port 53 //53是dns
port段
(tcp[0:2] > 1500 and tcp[0:2] < 1550) or (tcp[2:2] > 1500 and tcp[2:2] < 1550)
或
tcp portrange 1501-1549
指定协议：如：Ethernet type EAPOL，ip
ether proto 0x888e
ip
目标地址不是某个ethernet
not ether dst 01:80:c2:00:00:0e
除去广播数据
not broadcast and not multicast
显示http 80 get数据
port 80 and tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x47455420 GET 16进制是0x474554位过滤
IP Filters |
ip[0] & 0x0flow nibble: header length in 4octet words. should be 5ip[1]type of service/QoS/DiffServip[2:2]total length of datagram in octetsip[4:2]IP ID numberip[6] & 0x80reserved bit (possibly used for ECN)ip[6] & 0x40DF bitip[6] & 0x20MF bitip[6:2] & 0x1ffffragment offset (number of 8octet blocks)ip[8]ttlip[9]protocolip[10:2]header checksumip[12:4]source IPip[16:4]destination IPSamples (ip[12:4] = ip[16:4])Src IP = Dest IP (land attack)ip[0] & 0xf0high nibble: IP version. almost always 4(ip[0] & 0xf0 != 0x40)IP versions !=4(ip[0:1] & 0x0f > 5)IP with options set(ip[19] = 0xff)Broadcasts to x.x.x.255(ip[19] = 0x00)Broadcasts to x.x.x.0(ip and ip[1] & 0xfc == 0xb8)search for EF in DSCP(ip and ip[1] & 0xfc == 0x28)search for AF11 in DSCP(ip and ip[1] & 0xfc != 0x00)search for DCSP Packets != 0(ip[6] & 0x20 != 0) && (ip[6:2] & 0x1fff = 0)initial fragments(ip[6] & 0x20 != 0) && (ip[6:2] & 0x1fff != 0)intervening fragments(ip[6] & 0x20 = 0) && (ip[6:2] & 0x1fff != 0)terminal fragments(ip[0] & 0x0f) != 5has ip options (or is truncated, or is just some sort of freak...)ip[8] < 5short TTL valueip[6] = 32MF setiip[2:2] > 999IP Packet greater then 999 |
ICMP Filters |
icmp[0]typeicmp[1]codeicmp[2:2]checksumSamples icmp[0]=0x#all Packets with ICMP Typeicmp[0]=0x# and icmp[1]=0x#all Packets with ICMP Type X and Code = Yicmp[0]=8ICMP Request Messagesicmp[8]=0ICMP Request Replayicmp[0]=0x11ICMP Address Mask Requesticmp[0]=0x12ICMP Address Mask Replayicmp[0]=11 and icmp[1]=0ICMP Time Exeedeticmp[0]=3 and icmp[1]=4ICMP Time Exeedeticmp[0]=8 and ip[2:2] > 64Large ICMP Packets |
TCP Filters |
tcp[0:2]source porttcp[2:2]destination porttcp[4:4]sequence numbertcp[8:4]ack numbertcp[12]header lengthtcp[13]tcp flags ---- --S- 0000 0010 = 0x02 normal syn ---A --S- 0001 0010 = 0x12 normal syn-ack ---A ---- 0001 0000 = 0x10 normal ack --UA P--- 0011 1000 = 0x38 psh-urg-ack. interactive stuff like ssh ---A -R-- 0001 0100 = 0x14 rst-ack. it happens. ---- --SF 0000 0011 = 0x03 syn-fin scan --U- P--F 0010 1001 = 0x29 urg-psh-fin. nmap fingerprint packet -Y-- ---- 0100 0000 = 0x40 anything >= 0x40 has a reserved bit set XY-- ---- 1100 0000 = 0xC0 both reserved bits set XYUA PRSF 1111 1111 = 0xFF FULL_XMAS scantcp[14:2]window sizetcp[16:2]checksumttcp[18:2]urgent pointerSamples tcp[13] = 0x02is SYN. nothing else.(tcp[13] & 0x02) != 0contains SYN. we don't care what else...(tcp[13] & 0x03) = 3is some kind of SYN-FIN. realy Bad winnuke (not tested)tcp[20:4] = 0x47455420GET in request |
UDP Filters |
udp[0:2]source portudp[2:2]destination portudp[4:2]datagram lengthudp[6:2]UDP checksum |
protocols |
ip[9] == 8EGPip[9] == 9IGPip[9] == 88EIRGPip[9] == 50ESPip[9] == 51AHip[9] == 89OSPFip[9] == 124ISIS other, see /etc/protocols |
Routing Protocols |
(udp and port 520) or (host 224.0.0.9)RIP 1 + 2tcp and port 179BGPip[9] == 8EGPip[9] == 9IGPip[9] == 88EIRGPip[9] == 89OSPFip[9] == 124ISIS |
ether Filters |
ether[20:2] == 0x2000CDP paketsether[12:2] == 0x0806ARP pakets |
IPv6 |
ip6filters native IPv6 traffic (including ICMPv6)icmp6filters native ICMPv6 trafficproto ipv6filters tunneled IPv6-in-IPv4 trafficTCP ip6 and (ip6[6] == 0x06)IPv6 TCPip6 and (ip6[6] == 0x06) and (ip6[53] == 0x02)IPv6 TCP Synip6 and (ip6[6] == 0x06) and (ip6[53] == 0x10)IPv6 TCP ACKip6 and (ip6[6] == 0x06) and (ip6[53] == 0x12)IPv6 TCP Syn/ACKUDP ip6 and (ip6[6] == 0x11)IPv6 TCPICMP (ip6[6] == 0x3a)ICMP v6(ip6[6] == 0x3a) and (ip6[40] == 0x01)ipv6 and type 1 Dest Unreachable(ip6[6] == 0x3a) and (ip6[40] == 0x02)ipv6 and type 2 Packet too big(ip6[6] == 0x3a) and (ip6[40] == 0x03)ipv6 and type 3 Time Exeedet(ip6[6] == 0x3a) and (ip6[40] == 0x04)ipv6 and type 4 Parameter Problem(ip6[6] == 0x3a) and (ip6[40] == 0x80)ipv6 and type 128 Echo Request(ip6[6] == 0x3a) and (ip6[40] == 0x81)ipv6 and type 129 Echo Reply(ip6[6] == 0x3a) and (ip6[40] == 0x86)ipv6 and type 133 Router Solicitation(ip6[6] == 0x3a) and (ip6[40] == 0x87)ipv6 and type 134 Router Advertisement(ip6[6] == 0x3a) and (ip6[40] == 0x88)ipv6 and type 135 Neighbor Solicitation(ip6[6] == 0x3a) and (ip6[40] == 0x89)ipv6 and type 136 Neighbor Advertisement |
MY Filters |
tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'IP broadcast or multicast packets that were not sent via ethernet broadcast or multicast: |
