From: David S. Miller Date: Wed, 24 Jun 2015 09:16:03 +0000 (-0700) Subject: Merge branch 'ipv4-nexthop-link-status' X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=f389a40ec30f1c6c63eb61ec104d7c9886e1109a;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git Merge branch 'ipv4-nexthop-link-status' Andy Gospodarek says: ==================== changes to make ipv4 routing table aware of next-hop link status This series adds the ability to have the Linux kernel track whether or not a particular route should be used based on the link-status of the interface associated with the next-hop. Before this patch any link-failure on an interface that was serving as a gateway for some systems could result in those systems being isolated from the rest of the network as the stack would continue to attempt to send frames out of an interface that is actually linked-down. When the kernel is responsible for all forwarding, it should also be responsible for taking action when the traffic can no longer be forwarded -- there is no real need to outsource link-monitoring to userspace anymore. This feature is only enabled with the new per-interface or ipv4 global sysctls called 'ignore_routes_with_linkdown'. net.ipv4.conf.all.ignore_routes_with_linkdown = 0 net.ipv4.conf.default.ignore_routes_with_linkdown = 0 net.ipv4.conf.lo.ignore_routes_with_linkdown = 0 ... When the above sysctls are set, the kernel will not only report to userspace that the link is down, but it will also report to userspace that a route is dead. This will signal to userspace that the route will not be selected. With the new sysctls set, the following behavior can be observed (interface p8p1 is link-down): default via 10.0.5.2 dev p9p1 10.0.5.0/24 dev p9p1 proto kernel scope link src 10.0.5.15 70.0.0.0/24 dev p7p1 proto kernel scope link src 70.0.0.1 80.0.0.0/24 dev p8p1 proto kernel scope link src 80.0.0.1 dead linkdown 90.0.0.0/24 via 80.0.0.2 dev p8p1 metric 1 dead linkdown 90.0.0.0/24 via 70.0.0.2 dev p7p1 metric 2 90.0.0.1 via 70.0.0.2 dev p7p1 src 70.0.0.1 cache local 80.0.0.1 dev lo src 80.0.0.1 cache 80.0.0.2 via 10.0.5.2 dev p9p1 src 10.0.5.15 cache While the route does remain in the table (so it can be modified if needed rather than being wiped away as it would be if IFF_UP was cleared), the proper next-hop is chosen automatically when the link is down. Now interface p8p1 is linked-up: default via 10.0.5.2 dev p9p1 10.0.5.0/24 dev p9p1 proto kernel scope link src 10.0.5.15 70.0.0.0/24 dev p7p1 proto kernel scope link src 70.0.0.1 80.0.0.0/24 dev p8p1 proto kernel scope link src 80.0.0.1 90.0.0.0/24 via 80.0.0.2 dev p8p1 metric 1 90.0.0.0/24 via 70.0.0.2 dev p7p1 metric 2 192.168.56.0/24 dev p2p1 proto kernel scope link src 192.168.56.2 90.0.0.1 via 80.0.0.2 dev p8p1 src 80.0.0.1 cache local 80.0.0.1 dev lo src 80.0.0.1 cache 80.0.0.2 dev p8p1 src 80.0.0.1 cache and the output changes to what one would expect. If the global or interface sysctl is not set, the following output would be expected when p8p1 is down: default via 10.0.5.2 dev p9p1 10.0.5.0/24 dev p9p1 proto kernel scope link src 10.0.5.15 70.0.0.0/24 dev p7p1 proto kernel scope link src 70.0.0.1 80.0.0.0/24 dev p8p1 proto kernel scope link src 80.0.0.1 linkdown 90.0.0.0/24 via 80.0.0.2 dev p8p1 metric 1 linkdown 90.0.0.0/24 via 70.0.0.2 dev p7p1 metric 2 If the dead flag does not appear there should be no expectation that the kernel would skip using this route due to link being down. v2: Split kernel changes into 2 patches: first to add linkdown flag and second to add new sysctl settings. Also took suggestion from Alex to simplify code by only checking sysctl during fib lookup and suggestion from Scott to add a per-interface sysctl. Added iproute2 patch to recognize and print linkdown flag. v3: Code cleanups along with reverse-path checks suggested by Alex and small fixes related to problems found when multipath was disabled. v4: Drop binary sysctls v5: Whitespace and variable declaration fixups suggested by Dave v6: Style changes noticed by Dave and checkpath suggestions. v7: Last checkpatch fixup. Though there were some that preferred not to have a configuration option and to make this behavior the default when it was discussed in Ottawa earlier this year since "it was time to do this." I wanted to propose the config option to preserve the current behavior for those that desire it. I'll happily remove it if Dave and Linus approve. An IPv6 implementation is also needed (DECnet too!), but I wanted to start with the IPv4 implementation to get people comfortable with the idea before moving forward. If this is accepted the IPv6 implementation can be posted shortly. There was also a request for switchdev support for this, but that will be posted as a followup as switchdev does not currently handle dead next-hops in a multi-path case and I felt that infra needed to be added first. FWIW, we have been running the original version of this series with a global sysctl and our customers have been happily using a backported version for IPv4 and IPv6 for >6 months. ==================== Signed-off-by: David S. Miller --- f389a40ec30f1c6c63eb61ec104d7c9886e1109a