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Linux and Multiple Internet Uplinks: a New Tool
New submitter Alessandro Zarrilli writes: Linux has been able do multipath routing for a long time: it means being able to have routes with multiple gateways and to use them in a (weighted) round-robin fashion. But Linux is missing a tool to actively monitor the state of internet uplinks and change the routing accordingly. Without it, from a LAN perspective, it's like having a RAID-0: just one uplink goes down and all of your LAN-to-WAN traffic goes down too. Documentation and examples on the subject are lacking; existing solutions are few and deeply integrated in firewall/routing specific distributions. To address these issues, a new standalone tool was just released: Fault Tolerant Router. It also includes a complete (iptables + ip policy routing) configuration generator.
Strange.
I was using routing patches to Linux nearly 7 years ago to do this (admittedly it wasn't in the stock kernel, but the patches weren't huge)... you were able to specify multipath and multiple gateways and if one route went down, the others were prioritised and would take over, and also your upstream etc. were balanced properly and took account of failing routes automatically without any kind of daemon etc. running.
I ran a school off multiple ADSL and even 3G connections with it - the only manual maintenance I ever had to do was to put the ADSL modems onto a SMS-controlled relay (SMS came in on the same 3G stick!) because our ISP would often give us "dead" sessions if they'd had problems (where you'd get PPP and an IP and a remote gateway but couldn't do anything across them) and we were then able to manually reset if necessary. My bursar and I used the system for five years like that, only ever resetting it to enable VPN when all the upstream routes had got dead sessions, and that less than once or twice a year.
And, no, we didn't have to do much. It was a stock Slackware install with one set of patches to a (2.6?) kernel to enable the multipath routing etc. Pretty well advertised at the time, one plain page of simple patches (I remember porting them myself to a newer kernel version, just before the new diffs came out), I'll try and dig it up.
And "RAID-0 for upstream"? Bollocks. It "just worked" whatever interfaces were up (proven by it would even include the 3G PPP interface whenever it came up, and that only came up when we manually instructed it to connect as it cost money).
Not saying this isn't good software, but it's by far not the problem the summary purports it to be, not a first by any means, and certainly not "new".
There is a small shell script called gwping, which can be used to do the exactly same thing, easier and simpler. It's ~150 lines (with comments and everything) and takes 10-20 minutes to setup with the policy routing and everything, we don't need an overbloated runtime to do something so simple.