1

In a 3-way peering connection A to B and A to C. Can A address same instance IP/32 in both B and C via peering connection - I am not sure. Both B and C have matching /16 CIDRs.

Routing for Response Traffic - simply talks about A sending responses back to correct calling instance(in B).

enter image description here VPC Peering

But does not talk about instance in C calling A, neither A calling B or C. What will happen when same /32 from C calls A.

Improve this question

1 Answer 1

Reset to default
1

Form the drawing in the reference link that you provided the route table looks like this:

Destination Target 172.16.0.0/16 Local 10.0.1.0/24 pcx-aaaabbbb 10.0.0.0/24 pcx-aaaacccc

Therefore if Subnet A sends a packet in to an IP address in Subnet B (10.0.1.0/24), it will go to VPC B. Since the two Subnet Bs have overlapping CIDRs the route table will determine the destination. PCX-AAAABBBB has an entry for 10.0.1.0/24.

Instances in VPC C Subnet B will not be able to talk to VPC A as there is no return route back to VPC C. The response for those packets will either be dropped or sent to VPC B Subnet B.

Improve this answer
Sign up to request clarification or add additional context in comments.

5 Comments

Thx yes I get this explanation. My core question is: Can A call/address same instance IP/32 in both B and C via peering connection. How ?
VPC A cannot talk to VPC C Subnet B. There is no route. IF VPC A wants to talk to VPC C Subnet B IP 10.0.1.55 (for example) a "more specific" route could be added: 10.0.1.55/32 pcx-aaaaccc.
If both VPCs (B and C) have exact same IP 10.0.1.66/32 (as depicted) - how will A talk to both - how will a more specific route resolve the instance?
Your scenario is not supported by AWS.
Yes, that would be my general understanding too. So only way maybe is to change the IP, or eliminate the route completely prevent conflicts

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.