
D-7
Cisco PIX Firewall and VPN Configuration Guide
78-15033-01
Appendix D TCP/IP Reference Information
Using Subnet Masks
• Transmission Control Protocol (TCP)
• Trivial File Transfer Protocol (TFTP)
• User Datagram Protocol (UDP)
• RFC 1700
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, page D-7
• Uses for Subnet Information, page D-9
• Using Limited IP Addresses, page D-9
• Addresses in the .128 Mask, page D-9
• Addresses in the .192 Mask, page D-10
• Addresses in the .224 Mask, page D-10
• Addresses in the .240 Mask, page D-10
• Addresses in the .248 Mask, page D-11
• Addresses in the .252 Mask, page D-12
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 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
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