Subject: IP tracking for dual ISP on a srx Junos version tested on: 12.1r3
As internet links come cheaper we see more and more sites with dual ISP connections. Very often this is implemented with a high quality mean link and a cheap(er) backup line. When DSL or alike connections are used a failure occurs quite often at the WAN side of a router or DSL modem. A simple backup route in the routing table doesn’t help us in this case, the Ethernet side of the device stays up when the WAN side fails, so our SRX keeps the main route active. In the screenos devices we could use iptracking on the interface to deal with this problem. We can do something similar with Junos on the SRX. A little more complex to configure, but with (way) more control over what should be checked.
On Junos devices you can use the rpm (Realtime Performance Monitoring, don’t get confused you redhat users) implementation to do the monitoring for you. You can setuo full rpm with latency monitoring or even url tracking, but also a “simple” tracking with a ping packet is possible. For ISP tracking and failover this should be enough. We tested this and wrote this document about our findings.
See pdf for the complete document
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