Route Tables
6 posts tagged Route Tables.
You can route around the local route, and that is how intra-VPC inspection works
"The local route always wins and cannot be overridden" is the version most people learn. It is wrong in a specific and useful way: a route more specific than the VPC CIDR wins by longest prefix match, which is what makes inspecting traffic between two subnets possible.
Networking4 minA stale static route silently shadows the BGP route you are advertising
VPC route priority puts static routes above propagated ones at the same prefix. So a leftover static route wins over a healthy BGP advertisement, and the routing table looks correct because the route is there.
Networking4 minA 200 millisecond penalty is what a completely broken IPv6 path looks like
Happy Eyeballs means a dead address family costs you latency instead of errors. The fixed delay on dual-stack destinations is a specific enough fingerprint to diagnose from, and it can sit unnoticed indefinitely.
Networking4 minVPC peering has no reverse path forwarding, and AWS documents what that costs
A hub peered to two VPCs that share a CIDR will deliver one of them's replies to the other. AWS states the behaviour outright, and the configuration is legal to build because the overlap guardrail is narrower than people think.
Networking4 minThe misconfiguration that does not appear in the API output
A subnet with no explicit route table association is returned by nothing. DescribeRouteTables says so in one line of its own reference, and it means "check the route tables" structurally cannot find the problem.
Networking4 minOne Transit Gateway rule explains both an outage and a security hole
Route lookup happens against the route table associated with the attachment traffic arrived on. That single sentence produces a connection that should work and does not, and a connection that should be impossible and is not.
Networking4 min