1

Requirements for Internet Routers (Gateways) and Hosts

Relates to Lab 3. (Supplement)

Covers the compliance requirements of Internet routers and hosts.

2

What does it mean to be IP compliant?

• Requirements for Internet Routers and hosts have been document in Request for Comments (RFCs) of the Internet Engineering Task Force (IETF):

• RFC 985: Requirements for Internet Gateways – Draft (1986)• RFC 1009: Requirements for Internet Gateways (1987)• RDC 1716: Towards Requirements for IP Routers (1994)• RFC 1812: Requirements for IP Version 4 Routers (1995)• RFC 1122 (STD 3): Requirements for Internet Hosts - Communication

Layers (1989)• RFC 1123 (STD 3): Requirements for Internet Hosts - Application and

Support (1989)• Updated in many other RFCs

Language of Requirements

MUST – absolute requirement of the specification.

MUST IMPLEMENT – Implementation is required, but need not be enabled by default

MUST NOT – absolute prohibition of the specification.

SHOULD – there may exist valid reasons to, but full implications must be understood and weighed (recommended)

SHOULD NOT – there may exist valid reasons to include, but full implications must be understood and weighed (not recommended)

MAY / OPTIONAL – optional

3

Robustness Principle

"Be liberal in what you accept, and conservative in what you send”

• The principle should be applied by all protocols to increase robustness and interoperability

• Other hosts and routers may use deficient implementations

”Be Adaptive to Change" • Assume that protocol will be extended in the future, and

options will be added

4

HOST REQUIREMENTS: IPv4 (partial list)

5

HOST REQUIREMENTS: IPv4 (partial list)

6

HOST REQUIREMENTS: IPv4 (partial list)

7

Definition of an IP router (gateway)

1. Conforms to specific Internet protocols, including IP and ICMP

2. Interfaces to two or more packet networks– Encapsulation/decapsulation, MTU, address translation

3. Receives and forwards Internet datagrams. – Recognizes error conditions, Drop when TTL=0, perform

fragmentation

4. Chooses next hop

5. Supports a routing protocol

6. System Support (debugging, status report, etc.)

8

ROUTER REQUIREMENTS: IPv4 (partial list)

9

ROUTER REQUIREMENTS: IPv4 (partial list)

10

See RFC’s for more rules.

HOST REQUIREMENTS: IPv4 (partial list)

11

HOST REQUIREMENTS: IPv4 (partial list)

12

HOST REQUIREMENTS: IPv4 (partial list)

13

Definition of an IP router (gateway)

1. Conforms to specific Internet protocols, including IP and ICMP

2. Interfaces to two or more packet networks– Encapsulation/decapsulation, MTU, address translation

3. Receives and forwards Internet datagrams. – Recognizes error conditions, Drop when TTL=0, perform

fragmentation

4. Chooses next hop

5. Supports a routing protocol

6. System Support (debugging, status report, etc.)

14

ROUTER REQUIREMENTS: IPv4 (partial list)

15

ROUTER REQUIREMENTS: IPv4 (partial list)

16

See RFC’s for more rules.