Customer announces someone else's prefix; our filter blocks it¶
Case 22 of the Network Change Verdict Corpus. Category: filter-works. Expected verdict: safe (an experienced operator would approve it).
Why it is expected safe¶
ce1 starts announcing 8.8.8.0/24. pe1's customer filter rejects it, so nothing leaks. The customer-side change is bad, but our network behaves correctly, so a test of our network must pass.
The config change¶
Against the FRR configs of the base lab:
--- a/ce1.conf
+++ b/ce1.conf
@@ -18,3 +18,9 @@
neighbor 10.0.1.1 route-map ALLOW-ALL out
exit-address-family
!
+ip route 8.8.8.0/24 blackhole
+router bgp 65100
+ address-family ipv4 unicast
+ network 8.8.8.0/24
+ exit-address-family
+!
What each strategy said¶
The expected verdict was committed to git before any run. All three strategies tested the same running lab (method).
| Strategy | Verdict | Result | Checks that failed |
|---|---|---|---|
| Ping only | safe | ✅ | none |
| All BGP sessions up | safe | ✅ | none |
| Netdryrun intent checks | safe | ✅ | none |
What Netdryrun flagged¶
Nothing: every check in the intent spec passed, so Netdryrun called the change safe.
Reproduce it¶
On Linux or WSL2 with Docker and containerlab, from a checkout of the repository:
Case file: corpus/cases/22-customer-leaks-third-party.yml. Published result: netdryrun 0.2.0, containerlab 0.81.1, FRR quay.io/frrouting/frr:10.4.1, commit ec23379, run on 2026-10-26.