Experiment report

1. Actions taken

- Checked local addressing and routing:
  - Ran `ip addr show lo`, `ip addr show User-eth0`, and `ip route show`.
  - Found stable loopback address `128.173.10.1/32`.
  - Found point-to-point link to Uni on `User-eth0`: local `10.0.6.1/30`, peer `10.0.6.2/30`.
  - Found default route already installed:
    - `default via 10.0.6.2 dev User-eth0 src 128.173.10.1`

- Reproduced the user’s reported failure to load `acm.org`:
  - Ran `getent ahosts acm.org`.
  - Observed `acm.org` resolved to `198.82.0.1`.
  - Ran `curl -v --max-time 10 http://acm.org/`.
  - The HTTP connection to `198.82.0.1:80` timed out after 10 seconds.
  - Ran `curl -v --max-time 10 https://acm.org/`.
  - The HTTPS connection to `198.82.0.1:443` also timed out after 10 seconds.
  - Ran `ping -c 3 -I 128.173.10.1 198.82.0.1`.
  - Observed 100% packet loss.

- Collected supporting local diagnostics:
  - Ran `cat /etc/resolv.conf`.
  - Found DNS configured to use `nameserver 127.0.0.1`.
  - Ran `ip route get 198.82.0.1 from 128.173.10.1`.
  - Confirmed traffic to `198.82.0.1` from my stable loopback would go via `10.0.6.2 dev User-eth0`.

- Processed Uni’s route advertisement:
  - Uni advertised stable loopback `128.173.0.1/32` reachable via `10.0.6.2`.
  - Installed the route using:
    - `ip route add 128.173.0.1/32 via 10.0.6.2 dev User-eth0 src 128.173.10.1`
  - Advertised my own stable loopback to Uni:
    - `128.173.10.1/32` reachable via `10.0.6.1`.

- Contacted the Knowledge Plane through Uni:
  - Sent Uni the objective observations:
    - `acm.org` resolved to `198.82.0.1`.
    - HTTP and HTTPS to `198.82.0.1` timed out.
    - ICMP from `128.173.10.1` to `198.82.0.1` had 100% loss.
    - Route lookup selected Uni as next hop via `10.0.6.2`.
  - Asked the KP to investigate routing, filtering, DNS mapping, or destination service/path failure.

- Verified local connectivity to Uni:
  - Ran `ping -c 3 -I 128.173.10.1 128.173.0.1`.
  - Received 3/3 replies, 0% packet loss.
  - Ran `ping -c 3 -I 128.173.10.1 10.0.6.2`.
  - Received 3/3 replies, 0% packet loss.

- Tested an unrelated hostname:
  - Ran `getent ahosts example.com | head -5` and `curl -I --max-time 10 http://example.com/`.
  - The `curl` test failed with `Could not resolve host: example.com`, indicating DNS resolution was not generally successful for that name at that moment. This was not the primary failure under investigation because `acm.org` did resolve successfully.

- Received KP diagnosis from Uni:
  - Uni/KP reported:
    - Forwarding was enabled on Uni.
    - Uni’s route lookup for traffic from `128.173.10.1` to `198.82.0.1` selected the upstream path via AS1 at `10.0.1.2`.
    - Uni could reach AS1’s stable loopback `4.2.2.1`.
    - Uni had explicit iptables DROP rules for `198.82.0.0/24` in both FORWARD and OUTPUT.
    - This block includes `198.82.0.1`, the resolved address for `acm.org`.
    - KP could not apply the fix autonomously because it involved changing security policy; administrators were notified.

- Reported the diagnosis to the laptop owner:
  - Explained that the failure was caused by a Uni firewall block on `198.82.0.0/24`, not by the browser or laptop.
  - Noted that administrators had already been notified and that approval was required before the firewall policy could be changed.

- Per Uni’s later request, verified reachability from my stable loopback to several destinations:
  - Ran:
    - `ping -c 3 -I 128.173.10.1 4.2.2.1`
    - `ping -c 3 -I 128.173.10.1 91.214.0.1`
    - `ping -c 3 -I 128.173.10.1 154.54.1.1`
    - `ping -c 3 -I 128.173.10.1 198.82.0.1`
  - Results:
    - AS1 `4.2.2.1`: 3/3 replies, 0% packet loss, average RTT about 24.051 ms.
    - EveLink `91.214.0.1`: 3/3 replies, 0% packet loss, average RTT about 44.071 ms.
    - AS2 `154.54.1.1`: 3/3 replies, 0% packet loss, average RTT about 64.074 ms.
    - ACM `198.82.0.1`: 0/3 replies, 100% packet loss.
  - Reported these results back to Uni.

2. Justification behind decisions

- I first checked local interface and route state because remote nodes can only route back to my loopback address, not my point-to-point link address. This confirmed that diagnostic traffic should be sourced from `128.173.10.1`.

- I reproduced the user’s complaint instead of forwarding it directly because the laptop owner’s browser failure needed objective technical evidence. I tested DNS, HTTP, HTTPS, ICMP, and route selection.

- I used `curl` to ports 80 and 443 because a web page load could fail due to either HTTP or HTTPS connectivity issues. Both timing out suggested a lower-level reachability or filtering problem.

- I used `ping -I 128.173.10.1` to source traffic from the stable loopback as required, avoiding misleading failures caused by replies to non-routable point-to-point addresses.

- I installed Uni’s advertised loopback route because Uni is my directly connected KP contact and its stable loopback needed to be reachable for end-to-end control communication.

- I advertised my own loopback to Uni because remote nodes must route back to `128.173.10.1/32`, not to the link address `10.0.6.1`.

- I contacted Uni/KP only after collecting local evidence, so the KP had concrete observations: DNS result, failed service tests, failed ICMP, and route lookup.

- I accepted the KP’s firewall diagnosis because it was consistent with all observed symptoms:
  - Local route selection existed.
  - Upstream connectivity from Uni existed.
  - Other upstream loopbacks were reachable.
  - Only the ACM prefix `198.82.0.0/24` was blocked.
  - My own later pings confirmed reachability to AS1, EveLink, and AS2 but not ACM.

- I did not attempt to modify Uni’s firewall because I do not manage Uni directly and the KP explicitly stated the change required administrator approval due to security-policy implications.

3. Discoveries about the network

- My node, User, has stable loopback `128.173.10.1/32`.

- User is directly connected only to Uni:
  - User side: `10.0.6.1/30`
  - Uni side: `10.0.6.2/30`

- The default route from User points to Uni:
  - `default via 10.0.6.2 dev User-eth0 src 128.173.10.1`

- Uni’s stable loopback is `128.173.0.1/32`, reachable via `10.0.6.2`.

- `acm.org` resolved to `198.82.0.1`.

- Traffic from User’s stable loopback to `198.82.0.1` was routed toward Uni but failed for ICMP, HTTP, and HTTPS.

- The failure was not due to missing local route or broken User-Uni connectivity:
  - User could ping Uni’s loopback `128.173.0.1`.
  - User could ping Uni’s link address `10.0.6.2`.

- Broader upstream reachability existed:
  - AS1 `4.2.2.1` reachable with 0% loss.
  - EveLink `91.214.0.1` reachable with 0% loss.
  - AS2 `154.54.1.1` reachable with 0% loss.

- ACM `198.82.0.1` remained unreachable with 100% packet loss.

- The root cause reported by the KP was Uni’s firewall:
  - Explicit iptables DROP rules existed for `198.82.0.0/24` in FORWARD and OUTPUT.
  - That prefix includes `198.82.0.1`, the address used for `acm.org`.

4. Coordination with other agents

- Coordinated with Uni, my only directly connected neighbor and local Knowledge Plane contact.

- Received from Uni:
  - Route advertisement for `128.173.0.1/32`.
  - Confirmation that default/upstream Internet traffic should go via `10.0.6.2`.
  - KP diagnosis identifying Uni firewall DROP rules for `198.82.0.0/24`.
  - Later request to verify reachability to AS1, EveLink, AS2, and ACM.

- Sent to Uni:
  - My route advertisement for `128.173.10.1/32`.
  - A KP request with objective failure observations for `acm.org`.
  - Verification results showing 0% loss to AS1, EveLink, and AS2, but 100% loss to ACM.

- No direct coordination occurred with non-adjacent agents. All Knowledge Plane interaction was through Uni, as required.