Metrics (networking)
On computer networks, the metric defines a numerical measure of the quality of a connection when using a particular route.
With kindness can this be meant all the choice -influencing factors. Most often this refers to the available bandwidth, the connection quality or incurred monetary costs. It is also possible the delay, load, MTU, reliability and hop count into account. The metric used will decide whether a high or a low numerical value determines the quality of the route. For example, when considering the high bandwidth values are preferred. Specifies the metric, however, the monetary cost of a route in, you will prefer a low value. Thus there are several possible routes to the destination can be determined by the metric, which of these routes used for the connection.
Categories
Network metrics are particularly distinguished according to how calculated the value of a metric along a path from the individual metrics along this path. A distinction is made between additive, multiplicative and concave metrics.
Be a metric for a connection between the network nodes and, and be a path between nodes and. Then, the said metrics are defined as follows:
- Additive ( eg, delay in transmission )
- Multiplication ( eg loss probability)
- Concave: ( eg bandwidth )
Routing table
An example of the use of the metrics are routing tables that are used for routing the path finding. A decision is based on the metric that is to be used by multiple compounds in question. Depending on the used metric is usually the lowest ( eg, transmission delay ) or high ( eg bandwidth ) value.
Kernel IP routing table Destination Gateway Flags Metric Ref Use Iface Genmask 91.198.174.2 192.168.0.254 255.255.255.255 UGH 0 0 3 eth0 91.198.174.2 172.16.0.254 255.255.255.255 UGH 6 0 0 wlan0 192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 172.16.0.0 0.0.0.0 255.255.0.0 U 0 0 0 wlan0 0.0.0.0 172.16.0.254 0.0.0.0 UG 0 0 0 wlan0 In this example there are two network interface ( Iface column ), eth0 ( Wired) and wlan0 (Wireless LAN). For the IP address 91.198.174.2 there are two special host routes. These host routes are routes to a single computer, whereas so-called network routes a path to a network area have, so to a group of computers. The first entry with metric 3 states: If a path is searched to the IP address 91.198.174.2, trying to send the data packets through the interface named eth0 (cable). However, the second entry with metric 6 contains the instructions to send it via interface wlan0 (Wireless LAN). So there are two - to the value for the metric - similar entries that describe possible paths to the same destination. On the basis of the value is now chosen which interface to send to be used primarily. In the example would be all the packets (third and fourth entry ) are not intended for one of the two local networks, are routed through the wireless LAN to the default gateway (last entry ), unless it is to the target with the IP address 91.198.174.2, then would first attempt to take the path over the cable, because there the value of the metric is less.
Command to set a route with metric 1:
Route add -host 91.198.174.2 gw 192.168.0.254 metric 1 dev eth0 ( in GNU / Linux, Windows may be using a slightly different syntax)
The range of values of a metric can vary as widely as to determine the best route are only relative values of importance. Thus the allowed values for the metric in the EIGRP routing protocol are between 0 and ( = 4,294,967,295 ). When routing with Microsoft Windows XP, the range of values is, however, only 1-9999.