Building the ACM Cluster, Part 8: Adventures in Routing: Source Based (Multi-homed) Routing
Published on in ACM, ACM Cluster
(This post is related to the ACM cluster build. However, it is really generic systems stuff and not terribly related to the actual cluster build. It is much more closely related to quirks of JHU networking.)
The Problem
JHU has two distinct networks - firewalled and firewall-free. (In truth there are more and there are gradations, but these are the two JHUACM has IP allocations on.) Some services cannot be run form inside the firewalled network. For these the ACM has a small firewall-free allocation. Because the cluster will be hosting VMs inside both networks, it needs to be capable of routing traffic from both. This means doing something called source-based routing or multihomed routing. This refers to the fact that this machine will have two connections to the internet. Typically, this is a very rare setup - Multihoming is usually used at the ISP or datacenter level, rather than at the level of the individual box.
The Solution
The solution is to convert linux to …