** Changed in: linux (Ubuntu Zesty)
Status: New => Fix Committed
** Changed in: linux (Ubuntu Xenial)
Status: New => Fix Committed
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https://bugs.launchpad.net/bugs/1715812
Title:
Neighbour confirmation broken, breaks ARP cache aging
Status in linux package in Ubuntu:
Confirmed
Status in linux source package in Xenial:
Fix Committed
Status in linux source package in Zesty:
Fix Committed
Bug description:
[SRU Justification]
[Impact]
A host can lose access to another host whose MAC address changes if they have
active connections to other hosts that share a route. The ARP cache does not
time out as expected - instead the old MAC address is continuously reconfirmed.
[Fix]
Apply series [1], which changes the algorithm for neighbour confirmation.
That is, from upstream:
51ce8bd4d17a net: pending_confirm is not used anymore
0dec879f636f net: use dst_confirm_neigh for UDP, RAW, ICMP, L2TP
63fca65d0863 net: add confirm_neigh method to dst_ops
c3a2e8370534 tcp: replace dst_confirm with sk_dst_confirm
c86a773c7802 sctp: add dst_pending_confirm flag
4ff0620354f2 net: add dst_pending_confirm flag to skbuff
9b8805a32559 sock: add sk_dst_pending_confirm flag
[Test case]
Create 3 real or virtual systems, all hooked up to a switch.
One system needs an active-backup bond with fail_over_mac=1 num_grat_arp=0.
Put all the systems in the same subnet, e.g. 192.168.200.0/24
Call the system with the bond A, and the other two systems B and C.
On B, run in 3 shells:
- netperf -t TCP_RR to C
- ping -f A
- watch 'ip -s neigh show 192.168.200.0/24'
On A, cause the bond to fail over.
Observe that:
- without the patches, B intermittently fails to notice the change in
A's MAC address. This presents as the ping failing and not recovering,
and the arp table showing the old mac address never timing out and
never being replace with a new mac address.
- with the patches, the arp cache times out and B sends another mac
probe and detects A's new address.
It helps to use taskset to put ping and netperf on the same CPU, or
use single-CPU vms.
See [2] for more details.
[References]
[2] Original report:
https://www.mail-archive.com/netdev@vger.kernel.org/msg138762.html
[1]: https://www.spinics.net/lists/linux-rdma/msg45907.html
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