Preference of nexthop with source address broke ECMP for packets with source addresses which are not in the broadcast domain, but rather added to loopback/dummy interfaces. Original behaviour was to balance over nexthops while now it uses the latest nexthop from the group. For the case with 198.51.100.1/32 assigned to dummy0 and routed using 192.0.2.0/24 and 203.0.113.0/24 networks: 2: dummy0: mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000 link/ether d6:54:8a:ff:78:f5 brd ff:ff:ff:ff:ff:ff inet 198.51.100.1/32 scope global dummy0 valid_lft forever preferred_lft forever 7: veth1@if6: mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether 06:ed:98:87:6d:8a brd ff:ff:ff:ff:ff:ff link-netnsid 0 inet 192.0.2.2/24 scope global veth1 valid_lft forever preferred_lft forever inet6 fe80::4ed:98ff:fe87:6d8a/64 scope link proto kernel_ll valid_lft forever preferred_lft forever 9: veth3@if8: mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether ae:75:23:38:a0:d2 brd ff:ff:ff:ff:ff:ff link-netnsid 0 inet 203.0.113.2/24 scope global veth3 valid_lft forever preferred_lft forever inet6 fe80::ac75:23ff:fe38:a0d2/64 scope link proto kernel_ll valid_lft forever preferred_lft forever ~ ip ro list: default nexthop via 192.0.2.1 dev veth1 weight 1 nexthop via 203.0.113.1 dev veth3 weight 1 192.0.2.0/24 dev veth1 proto kernel scope link src 192.0.2.2 203.0.113.0/24 dev veth3 proto kernel scope link src 203.0.113.2 before: for i in {1..255} ; do ip ro get 10.0.0.$i; done | grep veth | awk ' {print $(NF-2)}' | sort | uniq -c: 255 veth3 after: for i in {1..255} ; do ip ro get 10.0.0.$i; done | grep veth | awk ' {print $(NF-2)}' | sort | uniq -c: 122 veth1 133 veth3 Fixes: 32607a332cfe ("ipv4: prefer multipath nexthop that matches source address") Signed-off-by: Vadim Fedorenko --- v1 -> v2: - add score calculation for nexthop to keep original logic - adjust commit message to explain the config - use dummy device instead of loopback --- net/ipv4/fib_semantics.c | 24 ++++++++---------------- 1 file changed, 8 insertions(+), 16 deletions(-) diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index a5f3c8459758..4d3650d20ff2 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -2167,8 +2167,8 @@ void fib_select_multipath(struct fib_result *res, int hash, { struct fib_info *fi = res->fi; struct net *net = fi->fib_net; - bool found = false; bool use_neigh; + int score = -1; __be32 saddr; if (unlikely(res->fi->nh)) { @@ -2180,7 +2180,7 @@ void fib_select_multipath(struct fib_result *res, int hash, saddr = fl4 ? fl4->saddr : 0; change_nexthops(fi) { - int nh_upper_bound; + int nh_upper_bound, nh_score = 0; /* Nexthops without a carrier are assigned an upper bound of * minus one when "ignore_routes_with_linkdown" is set. @@ -2190,24 +2190,16 @@ void fib_select_multipath(struct fib_result *res, int hash, (use_neigh && !fib_good_nh(nexthop_nh))) continue; - if (!found) { + if (saddr && nexthop_nh->nh_saddr == saddr) + nh_score += 2; + if (hash <= nh_upper_bound) + nh_score++; + if (score < nh_score) { res->nh_sel = nhsel; res->nhc = &nexthop_nh->nh_common; - found = !saddr || nexthop_nh->nh_saddr == saddr; + score = nh_score; } - if (hash > nh_upper_bound) - continue; - - if (!saddr || nexthop_nh->nh_saddr == saddr) { - res->nh_sel = nhsel; - res->nhc = &nexthop_nh->nh_common; - return; - } - - if (found) - return; - } endfor_nexthops(fi); } #endif -- 2.47.3