Understanding Networking Protocols
Networking protocols provide the rules needed for computers to communicate with each other on a network. Some of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocols, such as TCP and IP, provide basic connectivity. If you’re planning to take the Security+ exam, you should have a basic understanding of many of the different protocols and networking devices that have a relevance to security.
For example, can you answer this question?
Q. While reviewing logs on a firewall, you see several requests for the AAAA record of gcgapremium.com. What is the purpose of this request?
A. To identify the IPv4 address of gcgapremium.com
B. To identify the IPv6 address of gcgapremium.com
C. To identify the mail server for gcgapremium.com
D. To identify any aliases used by gcgapremium.com
More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation is available at the end of this post.
Common TCP/IP Protocols
TCP/IP isn’t a single protocol, but a full suite of protocols. If any of these protocols are completely new to you, you might want to do some additional research to ensure you understand the basics. These groups of protocols include:
- Basic connectivity protocols (TCP, UDP, IP, ICMP, ARP, NDP)
- Encryption protocols (SSH, SCP, SSL, TLS, IPsec)
- Application protocols (HTTP, HTTPS, FTP, SFTP, FTPS, TFTP)
- Email protocols (SMTP, POP3, IMAP4)
IPv4
IPv4 uses 32-bit IP addresses expressed in dotted decimal format. For example, the IPv4 IP address of 192.168.1.5 is four decimals separated by periods or dots. You can also express the address in binary form with 32 bits.
All Internet IP addresses are public IP addresses, and internal networks use private IP addresses. Public IP addresses are tightly controlled. You can’t just use any public IP address. Instead, you must either purchase or rent it. Internet Service Providers (ISPs) purchase entire ranges of IP addresses and issue them to customers. If you access the Internet from home, you are very likely receiving a public IP address from an ISP.
Routers on the Internet include rules to drop any traffic that is coming from or going to a private IP address, so you cannot use private IP addresses on the Internet. RFC 1918 specifies the following private address ranges:
- 10.x.y.z. 10.0.0.0 through 10.255.255.255
- 172.16.y.z–172.31.y.z. 172.16.0.0 through 172.31.255.255
- 192.168.y.z. 192.168.0.0 through 192.168.255.255
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IPv6
Although the number of IP addresses at first seemed inexhaustible, the Internet Assigned Numbers Authority (IANA) assigned the last block of IPv4 addresses in February 2011. To prepare, the Internet Engineering Task Force (IETF) created IPv6, which provides a significantly larger address space than IPv4.
IPv6 supports a significantly larger address space than IPv4 with over 340 undecillion IP addresses. For context, the order is billion, trillion, quadrillion, quintillion, sextillion, septillion, octillion, nonillion, decillion, and undecillion. Everyone will have enough addresses to assign IP addresses to their computers, TVs, mobile phones, refrigerators, coffeemakers, toasters, and anything else they might want to control remotely.
IPv6 uses 128-bit IP addresses expressed in hexadecimal format. For example, the IPv6 IP address of fe80:0000:0000:0000:02d4:3ff7:003f:de62 includes eight groups of four hexadecimal characters, separated by colons. Each hexadecimal character is composed of four bits.
You can simplify IPv6 addresses by omitting leading zeroes in any group of hexadecimal characters, and with zero compression. The IPv6 address looks like this with these two rules:
- Omit leading zeroes: fe80:0:0:0:2d4:3ff7:3f:de62
- Zero compression: fe80::02d4:3ff7:003f:de62
- Both rules: fe80::2d4:3ff7:3f:de62
The first example omits leading zeroes in five of the groups. Because you know that each group includes four characters, you know that any group with less than four characters is missing the leading zeroes. For example, :2d4 actually represents :02d4.
Zero compression substitutes a string of zeroes with two colons (::). For example, fe80::02d4:3ff7:003f:de62 is the same as fe80:0000:0000:0000:02d4:3ff7:003f:de62. You can only use one double colon in an IPv6 address.
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Another benefit of IPv6 over IPv4 is that it has more security built in. For example, the tunneling services provided by IPsec are built in to IPv6 and work natively with it. This allows you to encrypt just about any data in transit relatively easily, including older legacy protocols such as Telnet.
In contrast, IPsec isn’t native to IPv4 and it has some compatibility issues. For example, when IPsec passes through a device using Network Address Translation (NAT), NAT breaks IPsec. Although there are ways to work around the issues, IPv6 doesn’t have the same problems.
DNS, IPv4, and IPv6
Domain Name System (DNS) uses some different records for IPv6. As an example, DNS IPv4 uses A records (also called a host record) to map the host name to an IPv4 address. In contrast, IPv6 uses an AAAA record to map the host name to an IPv6 address. The Configuring DNS Servers blog post has more information some DNS records.
Remember this
IPv6 has a significantly larger address space than IPv4. IPsec is built in to IPv6 and can encrypt any type of IPv6 traffic.
Q. While reviewing logs on a firewall, you see several requests for the AAAA record of gcgapremium.com. What is the purpose of this request?
A. To identify the IPv4 address of gcgapremium.com
B. To identify the IPv6 address of gcgapremium.com
C. To identify the mail server for gcgapremium.com
D. To identify any aliases used by gcgapremium.com
Answer is B. A Domain Name System (DNS) AAAA record identifies the IPv6 address of a given name.
An A record identifies the IPv4 address of a given name.
An MX record identifies a mail server.
A CNAME record identifies aliases.
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