Experiment report for node Uni 1. Actions taken - Inspected Uni’s local addressing, interfaces, routes, and forwarding state: - Ran: - `ip addr show lo` - `ip addr show` - `ip route show` - `sysctl net.ipv4.ip_forward` - Found Uni’s stable loopback address: `128.173.0.1/32`. - Confirmed directly connected links: - `Uni-eth0` to User: Uni `10.0.6.2/30`, peer `10.0.6.1/30` - `Uni-eth1` to AS1: Uni `10.0.1.1/30`, peer `10.0.1.2/30` - Confirmed IPv4 forwarding was enabled: - `net.ipv4.ip_forward = 1` - Observed initial routing: - Default route via AS1: `default via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - Downstream User route: `128.173.10.1 via 10.0.6.1 dev Uni-eth0 src 128.173.0.1` - Advertised Uni’s stable loopback and known downstream reachability: - Sent AS1 a route update advertising: - Uni loopback `128.173.0.1/32` - downstream campus node `128.173.10.1/32` reachable via Uni - Sent User a route update advertising: - Uni loopback `128.173.0.1/32` - Uni’s role as the upstream/default gateway for campus traffic - Verified basic connectivity: - Ran: - `ping -c 3 -I 128.173.0.1 128.173.10.1` - `ping -c 3 10.0.1.2` - `ping -c 3 10.0.6.1` - Verified: - User loopback `128.173.10.1` was reachable from Uni’s loopback - AS1 link peer `10.0.1.2` was reachable - User link peer `10.0.6.1` was reachable - Audited local packet filtering and NAT state: - Ran: - `nft list ruleset` - `iptables -S` - `iptables -t nat -S` - Found: - Filter policies were ACCEPT - NAT had outbound masquerade: - `-A POSTROUTING -o Uni-eth1 -j MASQUERADE` - Requested route information from neighbors: - Asked AS1 to advertise its stable loopback and reachable upstream/service prefixes. - Asked User to advertise its loopback and any campus prefixes, and to confirm default routing via Uni. - Installed AS1-advertised upstream/service routes: - AS1 advertised: - AS1 loopback `4.2.2.1/32` - AS2 loopback `154.54.1.1/32` - ACM service prefixes `198.82.0.1/32` and `198.82.0.254/32` - EveLink `91.214.0.1/32` - Installed missing routes with: - `ip route add 4.2.2.1/32 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `ip route add 154.54.1.1/32 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `ip route add 198.82.0.1/32 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `ip route add 198.82.0.254/32 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `ip route add 91.214.0.1/32 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - Verified resulting routing table included: - `default via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `4.2.2.1 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `91.214.0.1 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `154.54.1.1 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `198.82.0.1 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `198.82.0.254 via 10.0.1.2 dev Uni-eth1 src 128.173.0.1` - `128.173.10.1 via 10.0.6.1 dev Uni-eth0 src 128.173.0.1` - Investigated User’s KP report that `acm.org` failed to load: - User reported: - DNS resolved `acm.org` to `198.82.0.1` - ICMP to `198.82.0.1` succeeded - TCP to ports 80 and 443 succeeded - TLS completed successfully - HTTP and HTTPS both returned `HTTP/1.1 503 Service Unavailable` - From Uni, I reproduced the symptom: - Ran: - `ping -c 3 -I 128.173.0.1 198.82.0.1` - HTTP GET using `nc` with source `128.173.0.1` - HTTPS GET using `curl` with source `128.173.0.1` - HTTP test returned: - `HTTP/1.1 503 Service Unavailable` - `Server: nginx/1.18.0` - body: `503 Service Unavailable` - HTTPS test returned the same 503 response. - Escalated the KP investigation upstream: - Sent AS1 a KP WHY request describing the local findings and User’s observations. - Asked AS1 to investigate or relay to ACM/responsible domain. - Did not report a final answer to User until AS1/ACM returned a definitive response. - Followed up with AS1 while the investigation was pending: - Sent a KP follow-up to AS1 after User requested status. - AS1 later confirmed it reproduced the same 503 from outside the university network and had relayed the request via AS2 to ACM. - Delivered final diagnosis to User: - After AS1 relayed ACM’s definitive response, I sent User the conclusion: - `CANNOT pending ACM administrator action` - Explained that no Uni, AS1, or AS2 routing/DNS/TCP/TLS/firewall/NAT change was indicated. - Performed final verification: - Ran: - `curl -4 -sk --interface 128.173.0.1 --resolve acm.org:443:198.82.0.1 -D /tmp/acm_final_headers -o /tmp/acm_final_body https://acm.org/` - Confirmed the symptom persisted: - `HTTP/1.1 503 Service Unavailable` - body: `503 Service Unavailable` 2. Justification behind decisions - I inspected local state first because Uni is the campus gateway and the KP policy requires local investigation before escalating. Routing, interface state, forwarding, firewall, and NAT are all possible causes of user connectivity failures. - I used Uni’s loopback address `128.173.0.1` as the source for non-adjacent diagnostics because link addresses are point-to-point infrastructure addresses and may not be routable remotely. - I advertised only stable loopback and downstream campus reachability, not point-to-point `/30` infrastructure links, because the link addresses are local to each physical connection and should not be advertised network-wide. - I accepted AS1’s small route advertisement because it contained a limited, plausible set of upstream/service loopback prefixes consistent with AS1’s role as Uni’s upstream ISP. It was not anomalously large. - I installed routes using only `ip route add`, as required. I did not use FRR, vtysh, bgpd, zebra, ospfd, or any routing daemon. - I audited firewall/NAT state but did not change it. Firewall and security enforcement changes require administrator approval, and the observed rules did not indicate a local block. - I did not report an early conclusion to User after only local reproduction. The KP policy requires waiting for a definitive FIX or CANNOT once a WHY request has been escalated. - I escalated to AS1 because the observed failure was beyond Uni’s local domain: DNS, ICMP, TCP, and TLS worked, while the remote web server returned HTTP 503. That strongly indicated a service/application-side issue. - I reported CANNOT only after ACM, via AS1 and AS2, confirmed that durable remediation required ACM administrator-approved action. 3. What was discovered about the network - Uni’s stable address is `128.173.0.1/32`. - User’s stable address is `128.173.10.1/32`. - AS1’s stable address is `4.2.2.1/32`. - Uni has two direct neighbors: - User over `10.0.6.0/30` - AS1 over `10.0.1.0/30` - Uni is correctly configured as a gateway: - IPv4 forwarding is enabled. - Default route points to AS1 at `10.0.1.2`. - User loopback route points to User at `10.0.6.1`. - Uni’s filtering/NAT state is permissive for forwarding: - Filter policies are ACCEPT. - NAT masquerades traffic outbound on `Uni-eth1`. - AS1 provides upstream reachability to: - `4.2.2.1/32` - `154.54.1.1/32` - `198.82.0.1/32` - `198.82.0.254/32` - `91.214.0.1/32` - default Internet transit - The `acm.org` issue was not caused by: - Uni routing - User default routing - AS1 routing - DNS resolution - ICMP reachability - TCP connectivity - TLS negotiation - Uni firewall or NAT - The confirmed issue was that ACM’s public web service at `198.82.0.1` was returning: - `HTTP/1.1 503 Service Unavailable` - from `nginx/1.18.0` - for both HTTP and HTTPS requests to `acm.org` 4. Coordination with other agents - Coordinated with User: - Received User’s route update: - User loopback `128.173.10.1/32` - default route confirmed via Uni at `10.0.6.2` - Received User’s KP investigation request for `acm.org`. - Later received follow-up test results from User confirming persistent HTTP 503. - Sent final diagnosis to User: - `CANNOT pending ACM administrator action` - Coordinated with AS1: - Sent route advertisement for Uni and campus reachability. - Received AS1 route advertisement and confirmation that AS1 had installed routes back to Uni and User. - Sent KP WHY request for the ACM service failure. - Sent follow-up requests while waiting for a definitive answer. - Received AS1’s interim diagnosis: - AS1 reproduced the HTTP 503 outside Uni. - AS1 escalated to ACM via AS2. - Received AS1’s definitive relay from ACM: - ACM confirmed the service-side 503. - ACM attempted low-risk remediation. - Durable fix requires ACM administrator approval. - Final status: CANNOT pending admin action. Final outcome Uni’s routing and gateway function were working correctly. The user-visible failure loading `acm.org` was traced to ACM’s own service returning HTTP/HTTPS 503. No Uni-side fix was appropriate or authorized. The final KP result was CANNOT pending ACM administrator action.