Steps to Ensure Direct Connect Connection is Used
Question
You work for an organization that has a Direct Connect Connection and a backup VPN connection.
This has been setup just recently.
After setting it up, the traffic flow still prefers the VPN connection instead of the Direct connection.
You have prepended a longer AS_PATH on the VPN connection , but even then this connection is being preferred.
Which of the below steps can be used to ensure the Direct Connect connection is used.
Answers
Explanations
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A. B. C. D.Answer - D.
It could be that the route being specified for the routing table is more specific for the VPN connection , hence this is being preferred.
The AWS Documentation clearly states that the most specific route in your route table that matches the traffic to determine how to route the traffic is used.
Hence it is better to ensure the VPN connection has a less specific route to ensure that it is not the preferred route which is taken.
For more information on Routing, please refer to below URL:
http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Route_Tables.html#route-tables-vgwWhen there are multiple connections to the same destination, the network routing protocol will choose the connection with the lowest cost or path. The path cost is calculated based on various factors such as the number of network hops, bandwidth, latency, and AS_PATH.
In this scenario, even after setting up Direct Connect and VPN connections, the traffic flow still prefers the VPN connection instead of the Direct Connect connection. To troubleshoot this issue, one of the following steps can be taken:
A. Remove the prepended AS_PATH: When a longer AS_PATH is advertised on the VPN connection, it increases the path cost, and the Direct Connect connection should be preferred. However, if even after this configuration, the VPN connection is still preferred, then removing the prepended AS_PATH may help. Removing the prepended AS_PATH will lower the path cost for the VPN connection, and the Direct Connect connection will be preferred.
B. Reconfigure the VPN as a static VPN instead of dynamic: The VPN connection can be configured as either a dynamic or a static VPN. In dynamic VPN, the VPN connection is established automatically using Border Gateway Protocol (BGP). In static VPN, the VPN connection is manually configured, and BGP is not used. Reconfiguring the VPN connection as a static VPN may help as it eliminates any potential issues with BGP configuration.
C. Increase the MED property on the VPN connection: Multiple paths to the same destination can be advertised with different MED (Multi-Exit Discriminator) values. When MED is used, the path with the lowest MED value is preferred. Increasing the MED value on the Direct Connect connection will make it more preferred than the VPN connection.
D. Advertise a less specific prefix on the VPN connection: If a less specific prefix is advertised on the VPN connection, the network routing protocol will prefer the more specific prefix advertised on the Direct Connect connection. For example, if the Direct Connect connection advertises a /24 prefix, and the VPN connection advertises a /20 prefix, advertising a /23 prefix on the VPN connection will make it less specific than the /24 prefix advertised on the Direct Connect connection. This will make the Direct Connect connection preferred over the VPN connection.
In conclusion, troubleshooting network routing issues require analyzing the routing protocol used and making necessary configuration changes to ensure the preferred path is used.
