Cisco PIX Firewall and VPN Configuration Guide, Version 6.2
TCP/IP Reference Information
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TCP/IP Reference Information

Table Of Contents

TCP/IP Reference Information

IP Addresses

Ports

Protocols and Applications

Supported Multimedia Applications

Supported Protocols and Applications

Using Subnet Masks

Masks

Uses for Subnet Information

With Limited IP Addresses

Addresses in the .128 Mask

Addresses in the .192 Mask

Addresses in the .224 Mask

Addresses in the .240 Mask

Addresses in the .248 Mask

Addresses in the .252 Mask


TCP/IP Reference Information


This appendix includes the following sections:

IP Addresses

Ports

Protocols and Applications

Using Subnet Masks

IP Addresses

IP address classes are defined as follows:

Class A— If the first octet is between 1 and 127 (inclusive), the address is a Class A address. In a Class A address, the first octet is the one-byte net address and the last three octets are the host address. The network mask for Class A addresses is 255.0.0.0.

Class B— If the first octet is between 128 and 191 (inclusive), the address is a
Class B address. In a Class B address, the first two octets are the net address and the last two octets are the host address. The network mask for Class B addresses is 255.255.0.0.

Class C— If the first octet is 192 or higher, the address is a Class C address. In a
Class C address, the first three octets are the net address and the last octet is the host address. The network mask for Class C addresses is 255.255.255.0.

Class D—These addresses are used for multicast transmissions and within the range from 224.0.0.0 to 239.255.255.255. Some of these addresses are assigned to multicasts used by specific TCP/IP protocols. Other Class D addresses are assigned to applications, such as streaming video, that send data to many recipients simultaneously. For information about enabling the PIX Firewall to transmit multicast traffic, refer to "Enabling Stub Multicast Routing" in Chapter 2, "Establishing Connectivity."

We recommend that you use RFC 1918 IP addresses for inside and perimeter addresses. These addresses follow:

Class A: 10.0.0.0 to 10.255.255.255

Class B: 172.16.0.0 to 172.31.255.255

Class C: 192.168.0.0 to 192.168.255.255

Class D: 224.0.0.0 to 239.255.255.255

PIX Firewall requires that IP addresses in the ip address, static, global, failover, and virtual commands be unique. These IP addresses cannot be the same as your router IP addresses.

In this guide, the use of "address" and "IP address" are synonymous.

IP addresses are primarily one of these values:

local_ip—An untranslated IP address on the internal, protected network. In an outbound connection originated from local_ip, the local_ip is translated to the global_ip. On the return path, the global_ip is translated to the local_ip. The local_ip to global_ip translation can be disabled with the nat 0 0 0 command. In syslog messages, this address is referenced as laddr.

global_ip—A translated global IP address in the pool or those addresses declared with the global or static commands. In syslog messages, this address is referenced as gaddr.

foreign_ip—An untranslated IP address on an external network. foreign_ip is an address for hosts on the external network. If the alias command is in use, an inbound message originating for the foreign_ip source address is translated to dnat_ip by PIX Firewall.

dnat_ip—(dual NAT) A translated (by the alias command) IP address on an external network. In an outbound connection destined to dnat_ip, it will be untranslated to foreign_ip. In syslog messages, this address is referenced as faddr.

virtual_ip—(used with the virtual command) A fictitious public or private IP address that is not the address of a real web server on the interface you are accessing. We recommend that you use an RFC 1918 address or one you make up.

Ports

The following literal names can be used instead of a numerical port value in command lines:

PIX Firewall permits the following TCP literal names: bgp, chargen, cmd, daytime, discard, domain, echo, exec, finger, ftp, ftp-data, gopher, h323, hostname, http, ident, irc, klogin, kshell, lpd, nntp, pop2, pop3, pptp, rpc, smtp, sqlnet, sunrpc, tacacs, talk, telnet, time, uucp, whois, and www.

PIX Firewall uses port 1521 for SQL*Net. This is the default port used by Oracle for SQL*Net. This value, however, does not agree with IANA port assignments.

PIX Firewall listens for RADIUS on ports 1645 and 1646. If your RADIUS server uses ports 1812 and 1813, you will need to reconfigure it to listen on ports 1645 and 1646.

Permitted UDP literal names are biff, bootpc, bootps, discard, dnsix, echo, mobile-ip, nameserver, netbios-dgm, netbios-ns, ntp, rip, snmp, snmptrap, sunrpc, syslog, tacacs, talk, tftp, time, who, and xdmcp.


Note To assign a port for DNS access, use domain, not dns. The dns keyword translates into the port value for dnsix.


Port numbers can be viewed online at the IANA website:

http://www.iana.org/assignments/port-numbers

Table D-1 lists the literal values.

Table D-1 Port Literal Values 

Literal
Value
Description

bgp

179

Border Gateway Protocol, RFC 1163

biff

512

Used by mail system to notify users that new mail is received

bootpc

68

Bootstrap Protocol Client

bootps

67

Bootstrap Protocol Server

chargen

19

Character Generator

cmd

514

Similar to exec except that cmd has automatic authentication

daytime

13

Day time, RFC 867

discard

9

Discard

domain

53

DNS (Domain Name System)

dnsix

195

DNSIX Session Management Module Audit Redirector

echo

7

Echo

exec

512

Remote process execution

finger

79

Finger

ftp

21

File Transfer Protocol (control port)

ftp-data

20

File Transfer Protocol (data port)

gopher

70

Gopher

hostname

101

NIC Host Name Server

nameserver

42

Host Name Server

ident

113

Ident authentication service

irc

194

Internet Relay Chat protocol

isakmp

500

ISAKMP

klogin

543

KLOGIN

kshell

544

Korn Shell

lpd

515

Line Printer Daemon - printer spooler

login

513

Remote login

mobile-ip

434

MobileIP-Agent

netbios-ns

137

NetBIOS Name Service

netbios-dgm

138

NetBIOS Datagram Service

nntp

119

Network News Transfer Protocol

ntp

123

Network Time Protocol

pim-auto-rp

496

Protocol Independent Multicast, reverse path flooding, dense mode

pop2

109

Post Office Protocol - Version 2

pop3

110

Post Office Protocol - Version 3

radius

1645, 1646

Remote Authentication Dial-In User Service

rip

520

Routing Information Protocol

smtp

25

Simple Mail Transport Protocol

snmp

161

Simple Network Management Protocol

snmptrap

162

Simple Network Management Protocol - Trap

sqlnet

1521

Structured Query Language Network

sunrpc

111

Sun RPC (Remote Procedure Call)

syslog

514

System Log

tacacs

49

TACACS+ (Terminal Access Controller Access Control System Plus)

talk

517

Talk

telnet

23

RFC 854 Telnet

tftp

69

Trivial File Transfer Protocol

time

37

Time

uucp

540

UNIX-to-UNIX Copy Program

who

513

Who

whois

43

Who Is

www

80

World Wide Web

xdmcp

177

X Display Manager Control Protocol, used to communicate between X terminals and workstations running UNIX


Protocols and Applications

This section provides information about the protocols and applications with which you may need to work when configuring PIX Firewall. It includes the following topics:

Supported Multimedia Applications

Supported Protocols and Applications

Possible literal values are ahp, eigrp, esp, gre, icmp, igmp, igrp, ip, ipinip, ipsec, nos, ospf, pcp, snp, tcp, and udp. You can also specify any protocol by number. The esp and ah protocols only work in conjunction with Private Link.


Note PIX Firewall does not pass multicast packets. Many routing protocols use multicast packets to transmit their data. If you need to send routing protocols across the PIX Firewall, configure the routers with the Cisco IOS software neighbor command. We consider it inherently dangerous to send routing protocols across the PIX Firewall. If the routes on the unprotected interface are corrupted, the routes transmitted to the protected side of the firewall will pollute routers there as well.


Table D-2 lists the numeric values for the protocol literals.

Table D-2 Protocol Literal Values 

Literal
Value
Description

ah

51

Authentication Header for IPv6, RFC 1826

eigrp

88

Enhanced Interior Gateway Routing Protocol

esp

50

Encapsulated Security Payload for IPv6, RFC 1827

gre

47

General Routing Encapsulation

icmp

1

Internet Control Message Protocol, RFC 792

igmp

2

Internet Group Management Protocol, RFC 1112

igrp

9

Interior Gateway Routing Protocol

ip

0

Internet Protocol

ipinip

4

IP-in-IP encapsulation

nos

94

Network Operating System (Novell's NetWare)

ospf

89

Open Shortest Path First routing protocol, RFC 1247

pcp

108

Payload Compression Protocol

snp

109

Sitara Networks Protocol

tcp

6

Transmission Control Protocol, RFC 793

udp

17

User Datagram Protocol, RFC 768


Protocol numbers can be viewed online at the IANA website:

http://www.iana.org/assignments/protocol-numbers

Supported Multimedia Applications

PIX Firewall supports the following multimedia and video conferencing applications:

CUseeMe Networks CU-SeeMe

CUseeMe Networks CU-SeeMe Pro

CUseeMe Networks MeetingPoint

Intel Internet Video Phone

Microsoft NetMeeting

Microsoft NetShow

NetMeeting

RealNetworks RealAudio and RealVideo

Point-to-Point Protocol over Ethernet (PPPoE)

VDOnet VDOLive

VocalTec Internet Phone

VXtreme WebTheater

Xing StreamWorks

Supported Protocols and Applications

PIX Firewall supports the following TCP/IP protocols and applications:

Address Resolution Protocol (ARP)

Archie

Berkeley Standard Distribution (BSD)-rcmds

Bootstrap Protocol (BOOTP)

Domain Name System (DNS)

File Transfer Protocol (FTP)

Generic Route Encapsulation (GRE)

Gopher

HyperText Transport Protocol (HTTP)

Internet Control Message Protocol (ICMP)

Internet Protocol (IP)

NetBIOS over IP (Microsoft Networking)

Point-to-Point Tunneling Protocol (PPTP)

Simple Network Management Protocol (SNMP)

Sitara Networks Protocol (SNP)

SQL*Net (Oracle client/server protocol)

Sun Remote Procedure Call (RPC) services, including Network File System (NFS)

Telnet

Transmission Control Protocol (TCP)

Trivial File Transfer Protocol (TFTP)

User Datagram Protocol (UDP)

Using Subnet Masks

This section lists information by subnet mask and identifies which masks are for networks, hosts, and broadcast addresses.


Note In some networks, broadcasts are also sent on the network address.


This section includes the following topics:

Masks

Uses for Subnet Information

With Limited IP Addresses

Addresses in the .128 Mask

Addresses in the .192 Mask

Addresses in the .224 Mask

Addresses in the .240 Mask

Addresses in the .248 Mask

Addresses in the .252 Mask

Masks

For the PIX Firewall commands that accept network masks, specify the correct mask for a network address. For hosts, use 255.255.255.255. However, for the ip address command, use a network mask, and for the global command, use a network address for both Port Address Translation (PAT) addresses and when specifying a pool of global addresses.

For the conduit and access-list commands, precede host addresses with the host parameter and without specifying a mask.

The following are examples of commands in which a mask can be specified:

ip address inside 10.1.1.1 255.255.255.0
ip address outside 209.165.201.1 255.255.255.224
nat (inside) 1 10.1.1.0 255.255.255.0
global (outside) 1 209.165.201.2 netmask 255.255.255.224
static (inside,outside) 209.165.201.3 10.1.1.3 netmask 255.255.255.255
access-list acl_out permit tcp any host 209.165.201.3 eq www
aaa authentication include http outside 209.165.201.3 255.255.255.255 0 0 TACACS+
route outside 0 0 209.165.201.4 1
telnet 10.1.1.2 255.255.255.255

In these examples, the ip address commands specify addresses for the inside and outside network interfaces. The ip address command only uses network masks. The inside interface is a Class A address, but only the last octet is used in the example network and therefore has a Class C mask. The outside interface is part of a subnet so the mask reflects the .224 subnet value.

The nat command lets users start connections from the inside network. Because a network address is specified, the class mask specified by the ip address inside command is used.

The global command provides a PAT address to handle the translated connections from the inside. The global address is also part of the subnet and contains the same mask specified in the ip address outside command.

The static command maps an inside host to a global address for access by outside users. Host masks are always specified as 255.255.255.255.

The access-list command permits any outside host to access the global address specified by the static command. The host parameter is the same as if you specified 209.165.201.3 255.255.255.255.

The aaa command indicates that any users wishing to access the global address must be authenticated. Because authentication only occurs when users access the specified global which is mapped to a host, the mask is for a host. The "0 0" entry indicates any host and its respective mask.

The route statement specifies the address of the default router. The "0 0" entry indicates any host and its respective mask.

The telnet command specifies a host that can access the PIX Firewall unit's console using Telnet. Because it is a single host, a host mask is used.

If you are using subnet masks, refer to "Using Subnet Masks," to be sure that each IP address you choose for global or static addresses is in the correct subnet.

The subnet masks are also identified by the number of bits in the mask. Table D-3 lists subnet masks by the number of bits in the network ID.

Table D-3 Masks Listed by Number of Bit

Network
ID Bits
Host ID Bits
Subnet
Example Notation
# of Subnets
# of Hosts on
Each Subnet

24

8

.0

192.168.1.1/24

1

254

25

7

.128

192.168.1.1/25

2

126

26

6

.192

192.168.1.1/26

4

62

27

5

.224

192.168.1.1/27

8

30

28

4

.240

192.168.1.1/28

16

14

29

3

.248

192.168.1.1/29

32

6

30

2

.252

192.168.1.1/30

64

2


The .255 mask indicates a single host in a network.

Uses for Subnet Information

Use subnet information to ensure that your host addresses are in the same subnet and that you are not accidentally using a network or broadcast address for a host.

The network address provides a way to reference all the addresses in a subnet, which you can use in the global, outbound, and static commands. For example, you can use the following net static command statement to map global addresses 192.168.1.65 through 192.168.1.126 to local addresses 192.168.2.65 through 192.168.2.126:

static (dmz1,dmz2) 192.168.1.64 192.168.2.64 netmask 255.255.255.192.

Subnet mask information is especially valuable when you have disabled Network Address Translation (NAT) using the nat 0 command. PIX Firewall requires that IP addresses on each interface be in different subnets.

However all the hosts on a PIX Firewall interface between the PIX Firewall and the router must be in the same subnet as well. For example, if you have an address such as 192.168.17.0 and you are not using NAT, you could use the 255.255.255.192 subnet mask for all three interfaces and use addresses 192.168.17.1 through 192.168.17.62 for the outside interface, 192.168.17.65 through 192.168.17.126 for the perimeter interface, and 192.168.17.129 through 192.168.17.190 for the inside interface.

With Limited IP Addresses

Another use for subnet mask information is for network planning when an Internet service provider (ISP) gives you a limited number of IP addresses and requires you to use a specific subnet mask. Use the information in this appendix to ensure that the outside addresses you choose are in the subnet for the appropriate subnet mask.

For example, if your ISP assigns you 192.168.17.176 with a subnet mask of .240, you can see in Table D-7, Subnet Number 12 for the .240 mask, that hosts can have IP addresses of 192.168.17.177 through 192.168.17.190. Because this only yields 14 hosts, you will probably use one for your router, another for the outside interface of the PIX Firewall, one for a static for a web server, if you have it, one for a static for your mail server, and the remaining 10 for global addresses. One of these addresses should be a PAT address so that you do not run out of global addresses.

Addresses in the .128 Mask

Table D-4 lists valid addresses for the .128 subnet mask. This mask permits up to 2 subnets with enough host addresses for 126 hosts per subnet.

Table D-4 .128 Network Mask Addresses

Subnet Number
Network Address
Starting Host Address
Ending Host Address
Broadcast Address

1

.0

.1

.126

.127

2

.128

.129

.254

.255


Addresses in the .192 Mask

Table D-5 lists valid addresses for the .192 subnet mask. This mask permits up to 4 subnets with enough host addresses for 62 hosts per subnet.

Table D-5 .192 Network Mask Addresses

Subnet Number
Network Address
Starting Host Address
Ending Host Address
Broadcast Address

1

.0

.1

.62

.63

2

.64

.65

.126

.127

3

.128

.129

.190

.191

4

.192

.193

.254

.255


Addresses in the .224 Mask

Table D-6 lists valid addresses for the .224 subnet mask. This mask permits up to 8 subnets with enough host addresses for 30 hosts per subnet.

Table D-6 .224 Network Mask Addresses 

Subnet Number
Network Address
Starting Host Address
Ending Host Address
Broadcast Address

1

.0

.1

.30

.31

2

.32

.33

.62

.63

3

.64

.65

.94

.95

4

.96

.97

.126

.127

5

.128

.129

.158

.159

6

.160

.161

.190

.191

7

.192

.193

.222

.223

8

.224

.225

.254

.255


Addresses in the .240 Mask

Table D-7 lists valid addresses for the .240 subnet mask. This mask permits up to 16 subnets with enough host addresses for 14 hosts per subnet.

Table D-7 .240 Network Mask Addresses 

Subnet Number
Network Address
Starting Host Address
Ending Host Address
Broadcast Address

1

.0

.1

.14

.15

2

.16

.17

.30

.31

3

.32

.33

.46

.47

4

.48

.49

.62

.63

5

.64

.65

.78

.79

6

.80

.81

.94

.95

7

.96

.97

.110

.111

8

.112

.113

.126

.127

9

.128

.129

.142

.143

10

.144

.145

.158

.159

11

.160

.161

.174

.175

12

.176

.177

.190

.191

13

.192

.193

.206

.207

14

.208

.209

.222

.223

15

.224

.225

.238

.239

16

.240

.241

.254

.255


Addresses in the .248 Mask

Table D-8 lists valid addresses for the .248 subnet mask. This mask permits up to 32 subnets with enough host addresses for 6 hosts per subnet.

Table D-8 .248 Network Mask Addresses 

Subnet Number
Network Address
Starting Host Address
Ending Host Address
Broadcast Address

1

.0

.1

.6

.7

2

.8

.9

.14

.15

3

.16

.17

.22

.23

4

.24

.25

.30

.31

5

.32

.33

.38

.39

6

.40

.41

.46

.47

7

.48

.49

.54

.55

8

.56

.57

.62

.63

9

.64

.65

.70

.71

10

.72

.73

.78

.79

11

.80

.81

.86

.87

12

.88

.89

.94

.95

13

.96

.97

.102

.103

14

.104

.105

.110

.111

15

.112

.113

.118

.119

16

.120

.121

.126

.127

17

.128

.129

.134

.135

18

.136

.137

.142

.143

19

.144

.145

.150

.151

20

.152

.153

.158

.159

21

.160

.161

.166

.167

22

.168

.169

.174

.175

23

.176

.177

.182

.183

24

.184

.185

.190

.191

25

.192

.193

.198

.199

26

.200

.201

.206

.207

27

.208

.209

.214

.215

28

.216

.217

.222

.223

29

.224

.225

.230

.231

30

.232

.233

.238

.239

31

.240

.241

.246

.247

32

.248

.249

.254

.255


Addresses in the .252 Mask

Table D-9 lists valid addresses for the .252 subnet mask. This mask permits up to 64 subnets with enough host addresses for 2 hosts per subnet.

Table D-9 .252 Network Mask Addresses 

Subnet Number
Network Address
Starting Host Address
Ending Host Address
Broadcast Address

1

.0

.1

.2

.3

2

.4

.5

.6

.7

3

.8

.9

.10

.11

4

.12

.13

.14

.15

5

.16

.17

.18

.19

6

.20

.21

.22

.23

7

.24

.25

.26

.27

8

.28

.29

.30

.31

9

.32

.33

.34

.35

10

.36

.37

.38

.39

11

.40

.41

.42

.43

12

.44

.45

.46

.47

13

.48

.49

.50

.51

14

.52

.53

.54

.55

15

.56

.57

.58

.59

16

.60

.61

.62

.63

17

.64

.65

.66

.67

18

.68

.69

.70

.71

19

.72

.73

.74

.75

20

.76

.77

.78

.79

21

.80

.81

.82

.83

22

.84

.85

.86

.87

23

.88

.89

.90

.91

24

.92

.93

.94

.95

25

.96

.97

.98

.99

26

.100

.101

.102

.103

27

.104

.105

.106

.107

28

.108

.109

.110

.111

29

.112

.113

.114

.115

30

.116

.117

.118

.119

31

.120

.121

.122

.123

32

.124

.125

.126

.127

33

.128

.129

.130

.131

34

.132

.133

.134

.135

35

.136

.137

.138

.139

36

.140

.141

.142

.143

37

.144

.145

.146

.147

38

.148

.149

.150

.151

39

.152

.153

.154

.155

40

.156

.157

.158

.159

41

.160

.161

.162

.163

42

.164

.165

.166

.167

43

.168

.169

.170

.171

44

.172

.173

.174

.175

45

.176

.177

.178

.179

46

.180

.181

.182

.183

47

.184

.185

.186

.187

48

.188

.189

.190

.191

49

.192

.193

.194

.195

50

.196

.197

.198

.199

51

.200

.201

.202

.203

52

.204

.205

.206

.207

53

.208

.209

.210

.211

54

.212

.213

.214

.215

55

.216

.217

.218

.219

56

.220

.221

.222

.223

57

.224

.225

.226

.227

58

.228

.229

.230

.231

59

.232

.233

.234

.235

60

.236

.237

.238

.239

61

.240

.241

.242

.243

62

.244

.245

.246

.247

63

.248

.249

.250

.251

64

.252

.253

.254

.255