Cluster IP Space

The cluster reaches the outside world through a small set of public IP addresses. Use them when configuring firewall whitelists or other allow-lists on remote services (license servers, data sources, SSH allow-lists) that the cluster needs to talk to.

Login Nodes

Login nodes connect directly to the internet — when you SSH out from one, the remote side sees the node’s own IP.

Node	IP Address
`login3.hpc.caltech.edu`	131.215.148.44
`login4.hpc.caltech.edu`	131.215.148.45
`vislogin3.hpc.caltech.edu`	131.215.148.91
`vislogin4.hpc.caltech.edu`	131.215.148.129

Head Nodes

Compute nodes don’t have direct internet access. Outbound traffic from a job NATs through one of the head nodes, so the remote side sees the head node’s IP rather than the compute node’s.

Node	IP Address
`head3.hpc.caltech.edu`	131.215.148.40
`head4.hpc.caltech.edu`	131.215.148.41

Whitelisting from a remote firewall

A job can land on any of the nodes above, so to avoid having to predict which one, whitelist all six public IPs at the remote end:

Node	IP Address
`login3.hpc.caltech.edu`	131.215.148.44
`login4.hpc.caltech.edu`	131.215.148.45
`vislogin3.hpc.caltech.edu`	131.215.148.91
`vislogin4.hpc.caltech.edu`	131.215.148.129
`head3.hpc.caltech.edu`	131.215.148.40
`head4.hpc.caltech.edu`	131.215.148.41

If the remote firewall doesn’t need to be that precise — or you’d rather not maintain six separate entries — you can allow the whole 131.215.148.0/24 subnet, which covers all of the addresses above (and the rest of the cluster’s network range).