From 8b251e8eb677b511d66e4a8fd235690122f403b2 Mon Sep 17 00:00:00 2001 From: Brandon Philips Date: Thu, 20 Mar 2014 11:28:12 -0700 Subject: [PATCH] network: dhcp: create explicit host route to gateway Some DHCP servers gives you a netmask of 255.255.255.255 so the gateway is not routable. Other DHCP client implementations look through the existing routes to figure out if they should add an explicit host route. See below for a link. However, it makes sense to just create the route explicitly whether it is needed or not since it is explicit, makes the dhcp route entries independent of other entries and saves us from knowing the state of the kernel tables. After patch route table on a machine with a network (common case): default via 10.0.2.2 dev ens3 10.0.2.0/24 dev ens3 proto kernel scope link src 10.0.2.15 10.0.2.2 dev ens3 scope link After patch route table on a machine without a network (this case): default via 10.240.0.1 dev ens4v1 10.240.0.1 dev ens4v1 scope link The code from dhcpcd that works around this issue is on line 637. https://android.googlesource.com/platform/external/dhcpcd/+/master/configure.c --- src/network/networkd-link.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c index 275ad97..f85ac8a 100644 --- a/src/network/networkd-link.c +++ b/src/network/networkd-link.c @@ -237,6 +237,7 @@ static int link_enter_set_routes(Link *link) { if (link->dhcp_lease) { _cleanup_route_free_ Route *route = NULL; + _cleanup_route_free_ Route *route_gw = NULL; struct in_addr gateway; r = sd_dhcp_lease_get_router(link->dhcp_lease, &gateway); @@ -253,6 +254,30 @@ static int link_enter_set_routes(Link *link) { return r; } + r = route_new_dynamic(&route_gw); + if (r < 0) { + log_error_link(link, "Could not allocate route: %s", + strerror(-r)); + return r; + } + + /* The dhcp netmask may mask out the gateway. Add an explicit + * route for the gw host so that we can route no matter the + * netmask or existing kernel route tables. */ + route_gw->family = AF_INET; + route_gw->dst_addr.in = gateway; + route_gw->dst_prefixlen = 32; + route_gw->scope = RT_SCOPE_LINK; + + r = route_configure(route_gw, link, &route_handler); + if (r < 0) { + log_warning_link(link, + "could not set host route: %s", strerror(-r)); + return r; + } + + link->route_messages ++; + route->family = AF_INET; route->in_addr.in = gateway; -- 1.8.5.2 (Apple Git-48)