ssh pub key auto passby

Scenario:
log in from you laptop to a cluster and then go from there to some other cluster. Need set up auto pass by my ssh pub key.

1. make sure add all you ssh key to ssh agent
ssh-add
ssh-add -l

2. ssh to the intermediate cluster with -A (auto passby):
ssh -A user@host
ssh-add -l

3. ssh to the destiny cluster:
ssh user@destiny