How does multihop choose it's route?

MikeyCarter · 02-20-2009, 10:51 AM

I was about to ask "how do I verify it works", but figured it out as I was typing the question:

Code:

ip route
192.168.50.0/24 dev ovirtbr0  proto kernel  scope link  src 192.168.50.1 
172.29.0.0/24 dev eth0  proto kernel  scope link  src 172.29.0.83  metric 1 
172.29.0.0/24 dev wlan0  proto kernel  scope link  src 172.29.0.84  metric 2 
192.168.122.0/24 dev virbr0  proto kernel  scope link  src 192.168.122.1 
default 
	nexthop via 172.29.0.2  dev eth0 weight 1
	nexthop via 172.29.0.2  dev wlan0 weight 1

ping -c 5 www.google.ca; route -Cn | grep -e Source -e 74.125.95
PING www.l.google.com (74.125.95.99) 56(84) bytes of data.
64 bytes from iw-in-f99.google.com (74.125.95.99): icmp_seq=1 ttl=245 time=48.2 ms
64 bytes from iw-in-f99.google.com (74.125.95.99): icmp_seq=2 ttl=245 time=63.3 ms
64 bytes from iw-in-f99.google.com (74.125.95.99): icmp_seq=3 ttl=245 time=45.7 ms
64 bytes from iw-in-f99.google.com (74.125.95.99): icmp_seq=4 ttl=245 time=50.9 ms
64 bytes from iw-in-f99.google.com (74.125.95.99): icmp_seq=5 ttl=245 time=47.8 ms

--- www.l.google.com ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4052ms
rtt min/avg/max/mdev = 45.785/51.228/63.327/6.266 ms
Source          Destination     Gateway         Flags Metric Ref    Use Iface
172.29.0.83     74.125.95.104   172.29.0.2            0      0        5 eth0
172.29.0.84     74.125.95.99    172.29.0.2            0      0        5 wlan0
74.125.95.104   172.29.0.83     172.29.0.83     l     0      0        4 lo
74.125.95.147   172.29.0.83     172.29.0.83     l     0      0        1 lo
172.29.0.84     74.125.95.99    172.29.0.2            0      0        0 eth0
172.29.0.83     74.125.95.147   172.29.0.2            0      0        2 eth0
172.29.0.83     74.125.95.147   172.29.0.2            0      0        0 wlan0
172.29.0.83     74.125.95.104   172.29.0.2            0      0        0 wlan0
74.125.95.99    172.29.0.84     172.29.0.84     l     0      0        4 lo

So now my question how does it choose the route? Is it simply a case of which interface responds first? Which theoretically would be the interface which has the least amount of traffic?

acid_kewpie · 02-20-2009, 11:00 AM

In general the route chosen is the most specific route with the lowest metric. so a route x/24 metric 10 would chosen over x/24 metric 20, and one to y/28 metric 10 would be chosen over y/24 metric 10.