** Description changed:

- Tools such as vpnc try to flush routes when run inside network
- namespaces by writing 1 into /proc/sys/net/ipv4/route/flush. This
- currently does not work because flush is not enabled in non-initial
- network namespaces.
- Since routes are per network namespace it is safe to enable
+ SRU Justification
+ 
+ Impact: Tools such as vpnc try to flush routes when run inside network 
namespaces by writing 1 into /proc/sys/net/ipv4/route/flush. This
+ currently does not work because flush is not enabled in non-initial network 
namespaces. Users have complained about this at various times (cf. Link: 
https://github.com/lxc/lxd/issues/4257).
+ 
+ Fix: Enable /proc/sys/net/ipv4/route/flush inside non-initial network
+ namespaces.
+ 
+ Regression Potential: None, since this didn't use to work before. Since
+ routes are per network namespace it is safe to enable
  /proc/sys/net/ipv4/route/flush in there.
  
- This has been reported against LXD a few times before
+ Test Case: Tested with LXD on a kernel with the patch applied and by
+ running vpnc successfully.
  
- Link: https://github.com/lxc/lxd/issues/4257
+ Target Kernels: All LTS kernels starting from 4.15. Kernel 5.3 has the
+ patchset upstream.
  
- Please backport this to our LTS kernels. :)
+ Patches:
+ 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5cdda5f1d6adde02da591ca2196f20289977dc56

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https://bugs.launchpad.net/bugs/1836912

Title:
  ipv4: enable route flushing in network namespaces

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