Exam ANS-C00 topic 1 question 81 discussion

C, and E. https://aws.amazon.com/premiumsupport/knowledge-center/vpc-resolve-port-allocation-errors/ Limit the number of connections that clients can make to a single destination. Keeplive reduce the number of new connection establish.

The issue with D is that you still only have ONE private subnet which has ONE route table. Having multiple default routes in a single route table won't work. Therefore, I will go with C and E.

From here: https://docs.aws.amazon.com/vpc/latest/userguide/vpc-nat-gateway.html Each IPv4 address can support up to 55,000 simultaneous connections to each unique destination. A unique destination is identified by a unique combination of destination IP address, the destination port, and protocol (TCP/UDP/ICMP). You can increase this limit by associating up to 8 IPv4 addresses to your NAT Gateways (1 primary IPv4 address and 7 secondary IPv4 addresses). You are limited to associating 2 Elastic IP addresses to your public NAT gateway by default. You can increase this limit by requesting a quota adjustment. For more information, see Elastic IP addresses.

C & E make sense

C and E as per the link: https://aws.amazon.com/premiumsupport/knowledge-center/vpc-resolve-port-allocation-errors/

Why A. is wrong: You can associate exactly one Elastic IP address with a public NAT gateway. You cannot disassociate an Elastic IP address from a NAT gateway after it's created. To use a different Elastic IP address for your NAT gateway, you must create a new NAT gateway with the required address, update your route tables, and then delete the existing NAT gateway if it's no longer required. Ref: https://docs.aws.amazon.com/vpc/latest/userguide/vpc-nat-gateway.html

B and E

D&E are correct

https://aws.amazon.com/premiumsupport/knowledge-center/vpc-resolve-port-allocation-errors/?nc1=h_ls ・Create a NAT gateway in each Availability Zone, and then distribute your clients across Availability Zones. Route traffic to the internet using a NAT gateway in the same Availability Zone as your client to reduce cross Availability Zone data charges.

Keepalive is implemented on server side, not client. might help reduce network congestion if same client , reaccess server. B and E

B & E for me....HTTP Keepalive to keep the TCP session open and NAT gateways to distribute the load and avoid port exhaustion on the NAT Gateway

C,E https://docs.aws.amazon.com/vpc/latest/userguide/nat-gateway-troubleshooting.html

TCP keep alive doesn't mean reusing the TCP connection. HTTP-keep alive does. Therefore answer should be B & E.

Answers A and D are not correct at all. It’s the tie between B and C HTTP keep alive can set the timeout and number if request, which is potential resolution as per below site https://aws.amazon.com/premiumsupport/knowledge-center/vpc-resolve-port-allocation-errors/ TCP keep alive on the other hand is a way to keep the connection active so might not work here. So my answers are B E

C is wrong We have an HTTP connexion built on top of a TCP socket Without HTTP keepalive, the client connects to the server (through TCP), make a request, then disconnects. That disconnect shutdown the TCP connection, that will never be used again. With HTTP keepalive, the client connects to the server (through TCP), make a request, then keep the connection UP, just in case. If 10sec later, a new request has to be made, it will use the existing connection. So, if you have no HTTP keepalive, TCP keepalive is useless, because the connection will not timeout : it will be shutdown on purpose Answers are B && E

Keepalive actually helps reduce the number of sessions. The NAT gateway will keep an orphan session for up to 350 seconds before releasing the port. If the instance uses a keepalive every 30 seconds, it will detect that the session is dead and it will sent an RST packet to reset it. NAT gateway will release the session upon receiving the RST packet as well. CE are correct

CE https://docs.aws.amazon.com/vpc/latest/userguide/nat-gateway-troubleshooting.html#nat-gateway-troubleshooting-timeout