AWS Route Limitation
An AWS VGW carries a hard limit of 100 BGP routes in total. When the BGP prefixes exceed 100, VGW randomly resets the BGP session, leading to unpredictable potential network downtime.
AWS publishes VPC limits at this link.
In addition to limits, there are limitations in functionality.
Below is a list of commonly asked limits and limitations by network engineers.
Functions | Limits | Comments |
---|---|---|
VPC Peering Limit per VPC |
125 |
Default limit is 50. Constrained also by route limit of 100 |
VPC Route entries in a route table |
100 |
Default is 50. Performance impact on 100 routes. |
BGP prefix total on VGW |
100 |
Exceeding the limit results in random BGP resets |
VGW instance size scaling DNAT function in VGW SNAT function in VGW NAT Gateway policies VPN connections per VPC |
reset BGP not available not available not available 10 |
Trigger a BGP downtime |
VPN traffic initiation VIF per Direct Connect |
from on-prem 50 |
Traffic must be initiated from on-prem to establish a VPN tunnel with VGW |
Inter region peering MTU size |
1500 bytes |
Unlike intra region peering, there is no jumbo frame support, therefore inter region performance is maxed out at 5Gbps. |
Outgoing SMTP traffic on port 25 |
throttled |
You can send a request to lift the throttle. |
I have more than 100 VPCs. How do I overcome AWS Route Limits (100)?
When AWS VGW carries more than 100 routes, its BGP session will crash unexpectedly, resulting in your network outage.
Azure network has similar limitations; the following techniques work for both cloud providers.
These are the options Aviatrix solution provides:
1. Summarizing Spoke VPC/VNet Routes
Enable Spoke VPC route summarization so that Aviatrix Transit Gateway advertises as few routes to VGW as possible. As long as you can limit the number of total routes on the VGW to less than 100, the Aviatrix Transit Network can support as many Spoke VPC/VNets as you need.
Aviatrix Controller sends alert and warning messages when it determines that the total routes carried by the VGW exceeds 80. This is to alert you to start reducing routes carried by the VGW to avoid potential network outage. This alert message is sent each time there is a route VGW advertised from VGW to Transit GW.
2. Bypassing VGW
To permanently solve the route limit problem and not have to worry about summarizing routes, use External Device Option to connect to on-prem directly over Direct Connect or the Internet.