Validate host IP, UDP, and TCP duties at their layer boundaries

Keep this document to one review outcome: Validate host IP, UDP, and TCP duties at their layer boundaries. Only the official source and traced locations below supply facts. Confirm applicability before acting.

Source fact:

The official RFC 1122 — Requirements for Internet Hosts – Communication Layers from RFC Editor supports the following bounded statements:

• A host must verify the IPv4 header checksum on every received datagram and silently discard a datagram with a bad checksum. The research record locates this support at Section 3.2.1.2 (Checksum).
• A host must generate and validate UDP checksums, enable checksum generation by default, and silently discard a received nonzero checksum that is invalid. The research record locates this support at Section 4.1.3.4 (UDP Checksums).
• For an active TCP open on a multihomed host with no chosen local address, TCP must ask IP to select one before the first SYN and retain it for later segments. The research record locates this support at Section 4.2.3.7 (TCP Multihoming).

Do not import neighboring assumptions into the source record. The supported task is a scoped comparison involving address plans, interfaces, routes, peers, protocol roles, timers, middleboxes, and intended failure domains and the conditions the source actually describes.

What the source does not establish

This RFC evidence supports only the named network-protocol decision; it does not select vendor settings, topology, capacity, or an acceptable failure mode. A correct source interpretation can still be inapplicable to a particular design. Confirm DNS, Active Directory authentication, PKI, time, routing policy, transport reachability, and monitoring, ownership, and change authority instead of treating documented behavior as a deployment guarantee.

Applicability questions

• For source statement 1 at Section 3.2.1.2 (Checksum), which observable configuration, record, or test can confirm applicability here?
• For source statement 2 at Section 4.1.3.4 (UDP Checksums), which observable configuration, record, or test can confirm applicability here?
• For source statement 3 at Section 4.2.3.7 (TCP Multihoming), which observable configuration, record, or test can confirm applicability here?
• Within address plans, interfaces, routes, peers, protocol roles, timers, middleboxes, and intended failure domains, which versions, roles, and configuration states define the review population?
• Could DNS, Active Directory authentication, PKI, time, routing policy, transport reachability, and monitoring invalidate the test, hide a failure, or change applicability?
• Who owns the decision, and which observation requires stopping, escalation, or rollback?

DSE recommendation:

DSE recommends using the cited source as the evidence anchor for this decision. Use a two-person review for the source interpretation and the resulting operational decision. Record the source location, examined part of address plans, interfaces, routes, peers, protocol roles, timers, middleboxes, and intended failure domains, observed and expected states, owner, and reason for deviation.

An implementation decision needs an owner, approved window, prechecks, observable outcome, stop authority, and rollback path. Validate DNS, Active Directory authentication, PKI, time, routing policy, transport reachability, and monitoring before and after the test, and store only sanitized operational evidence.

Verification and evidence

Tie each conclusion back to Section 3.2.1.2 (Checksum); Section 4.1.3.4 (UDP Checksums); Section 4.2.3.7 (TCP Multihoming) and to observable material such as configuration snapshots, route or neighbor state, packet captures, counters, topology records, and controlled failover results. Preserve provenance and stable identifiers without copying secrets into the evidence set.

Preserve both successful and failed observations, along with approval and rollback evidence. Avoid uncontrolled production experiments. Assign an expiry or event-driven recheck so the conclusion is not treated as permanent.

Official references

• RFC 1122 — Requirements for Internet Hosts – Communication Layers — RFC Editor