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 MUST SHOULD MAY SHOULD NOT MUST NOT Implement IP and ICMP ✔ Multiple IP addresses (“multihoming”) - local host - remote host ✔ ✔ Forward datagram received from connected network ✔ Silently discard version number ≠ 4 ✔ Able to log discarded datagrams ✔ Src address must be host's own IP address ✔ Support reassembly ✔

HOST REQUIREMENTS: IPv4 (partial list) 6 MUST SHOULD MAY SHOULD NOT MUST NOT Timestamp IP option Source route IP option ✔ ✔ Send packet with TTL of 0 Discard received packets with TTL < 2 Transport layer can set TTL ✔ ✔✔✔✔ Send ICMP for ICMP Error message Send ICMP for broadcast or multicast IP datagram Send ICMP error message (if not prohibited) ✔ ✔✔✔✔ Generate ICMP Dest Unreachable (code 2/3) Send ICMP Redirect Update routing table for incoming ICMP Redirect ✔ ✔ ✔ ICMP Echo Request and Reply (client and server) Discard Echo Request to broadcast address ✔ ✔

HOST REQUIREMENTS: IPv4 (partial list) 7 MUST SHOULD MAY SHOULD NOT MUST NOT Use netmask in local/remote decision for outgoing packets ✔ Operate without router or connected network ✔ Use default gateway if no match in routing table ✔ Ping routers continuously ✔ Use broadcast address as src IP address ✔

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 MUST SHOULD MAY SHOULD NOT MUST NOT Drop packets because unused IP header field values Ignore unrecognized IP options ✔ ✔ Check IP header checksum ✔ Support IP fragmentation First fragment is smallest Send fragments in order Generate least possible number of fragments ✔ ✔✔✔✔ ✔ Decrement TTL by at least one Discard packet when TTL is zero Send ICMP Error due to dropped packet with TTL=0 Generate packet with TTL=0 ✔✔✔✔ ✔ ✔

ROUTER REQUIREMENTS: IPv4 (partial list) 10 MUST SHOULD MAY SHOULD NOT MUST NOT Router must operate as a stand-alone device ✔ Be able to reboot from NOC Have mechanism for retrieving status ✔ Forward destination Forward destination with host number all `1’ Discard packets with host number all `1’ ✔ ✔✔✔✔ ✔ See RFC’s for more rules.

HOST REQUIREMENTS: IPv4 (partial list) 11 MUST SHOULD MAY SHOULD NOT MUST NOT Implement IP and ICMP ✔ Multiple IP addresses (“multihoming”) - local host - remote host ✔ ✔ Forward datagram received from connected network ✔ Silently discard version number ≠ 4 ✔ Able to log discarded datagrams ✔ Src address must be host's own IP address ✔ Support reassembly ✔

HOST REQUIREMENTS: IPv4 (partial list) 12 MUST SHOULD MAY SHOULD NOT MUST NOT Timestamp IP option Source route IP option ✔ ✔ Send packet with TTL of 0 Discard received packets with TTL < 2 Transport layer can set TTL ✔ ✔✔✔✔ Send ICMP for ICMP Error message Send ICMP for broadcast or multicast IP datagram Send ICMP error message (if not prohibited) ✔ ✔✔✔✔ Generate ICMP Dest Unreachable (code 2/3) Send ICMP Redirect Update routing table for incoming ICMP Redirect ✔ ✔ ✔ ICMP Echo Request and Reply (client and server) Discard Echo Request to broadcast address ✔ ✔

HOST REQUIREMENTS: IPv4 (partial list) 13 MUST SHOULD MAY SHOULD NOT MUST NOT Use netmask in local/remote decision for outgoing packets ✔ Operate without router or connected network ✔ Use default gateway if no match in routing table ✔ Ping routers continuously ✔ Use broadcast address as src IP address ✔

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 MUST SHOULD MAY SHOULD NOT MUST NOT Drop packets because unused IP header field values Ignore unrecognized IP options ✔ ✔ Check IP header checksum ✔ Support IP fragmentation First fragment is smallest Send fragments in order Generate least possible number of fragments ✔ ✔✔✔✔ ✔ Decrement TTL by at least one Discard packet when TTL is zero Send ICMP Error due to dropped packet with TTL=0 Generate packet with TTL=0 ✔✔✔✔ ✔ ✔

ROUTER REQUIREMENTS: IPv4 (partial list) 16 MUST SHOULD MAY SHOULD NOT MUST NOT Router must operate as a stand-alone device ✔ Be able to reboot from NOC Have mechanism for retrieving status ✔ Forward destination Forward destination with host number all `1’ Discard packets with host number all `1’ ✔ ✔✔✔✔ ✔ See RFC’s for more rules.