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user1274878
user1274878

Reputation: 1415

EC2 instance drops ICMP packets. How to measure the latency?

I am trying to measure the latency between one of my machines, and an EC2 instance. EC2 instances cannot be pinged. So I tried using application level timestaps (using gettimeofday()). I send a tcp packet with a timestamp in the payload.

Upon receiving this packet, I calculate the timestamp on my machine, and obtain the difference. It always comes out to be negative. My guess was that the clocks in the two machines could be skewed. So I used ntp to synchronize both the machines, but the problem still persists.

Can someone please help.

Upvotes: 0

Views: 641

Answers (2)

Michael - sqlbot
Michael - sqlbot

Reputation: 179314

EC2 instances can be pinged, if configured to allow it. I set one up for this today while trying to track down packet drops in us-west-2. In the security group protecting the instance, you add a rule to permit "ICMP Echo Request" from the source address of the machine where you're originating the ping.

Upvotes: 2

SamV
SamV

Reputation: 7586

See the AWS FAQ for this quote.

Why can't I ping my instance? Ping uses ICMP ECHO, which by default is blocked by your firewall. You'll need to grant ICMP access to your instances by updating the firewall restrictions that are tied to your security group.

ec2-authorize default -P icmp -t -1:-1 -s 0.0.0.0/0

Check out the latest developer guide for details.

Section: Instance Addressing and Network Security -> Network Security -> Examples

Upvotes: 1

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