Test Linux weird behavior on ECMP routes

ecmp_weird_route.sh

#!/bin/sh -e

NS=testns

BR1=testbr1
VETH1=testveth1
BR2=testbr2
VETH2=testveth2
LINKS="$VETH1 $VETH2 $BR1 $BR2"

NET1=192.168.11.xx/24
NET2=192.168.12.xx/24
IPNS="ip netns exec $NS ip"

clean() {
    for l in $LINKS; do
        if ip -o link show $l >/dev/null 2>&1; then
            ip link del $l
        fi
    done

    if ip netns list | grep -q $NS; then
        #ip netns exec $NS ip link del node0
        ip netns del $NS
    fi
}
trap clean INT QUIT TERM HUP PIPE 0

make_address() {
    local net addr
    net=$1
    addr=$2

    echo $net | sed "s/xx/$addr/"
}

cidr2ip() {
    echo $1 | cut -d / -f 1
}

GW1=$(make_address $NET1 1)
GW2=$(make_address $NET2 1)
ADDR1=$(make_address $NET1 2)
ADDR2=$(make_address $NET2 2)

setup_veth() {
    local br veth dest
    br=$1
    veth=$2
    dest=$3

    ip link add $br type bridge
    ip link add $veth type veth peer name ${veth}_
    ip link set $br up
    ip link set $veth master $br up
    ip link set ${veth}_ netns $NS name $dest up
}

setup() {
    ip netns add $NS
    $IPNS link set lo up

    setup_veth $BR1 $VETH1 eth0
    setup_veth $BR2 $VETH2 eth1

    local gw1 gw2
    ip addr add $GW1 dev $BR1
    ip addr add $GW2 dev $BR2
    $IPNS addr add $ADDR1 dev eth0
    $IPNS addr add $ADDR2 dev eth1

    $IPNS route add 0.0.0.0/0 nexthop via $(cidr2ip $GW1) nexthop via $(cidr2ip $GW2)
}

setup_node0() {
    $IPNS link add node0 type dummy
    $IPNS link set node0 up
    $IPNS addr add 192.168.10.2/32 dev node0
}

test_route_from() {
    local dest dev from r rdev
    dest=$1
    dev=$2
    from=$3
    r=$($IPNS -o route get $dest from $from)
    rdev=$(echo $r | sed -nr 's/^.*dev (eth[[:digit:]]+).*/\1/p')
    if [ "$dev" != "$rdev" ]; then
        echo "WRONG dev/from pair: ip -o route get $dest from $from:"
        printf "%s\n" "$r"
        return
    fi
}

test_route() {
    test_route_from "$1" eth0 $(cidr2ip $ADDR1)
    test_route_from "$1" eth1 $(cidr2ip $ADDR2)
}

run_tests() {
    test_route 12.34.56.78
    test_route 216.58.200.160
    test_route 216.58.200.161
    test_route 216.58.200.162
    test_route 216.58.200.163
    test_route 216.58.200.164
    test_route 52.85.149.10
    test_route 52.85.149.11
    test_route 52.85.149.12
    test_route 52.85.149.13
    test_route 52.85.149.14
}

# main
setup
#setup_node0
run_tests
read -p "Press enter to finish" ret