Lucent Technologies Release 8.2 manual LAN1, LAN2

Networking Screens		A Screens Reference
Metric	The metric value indicates the desirability of the IP route in terms of the efficiency of
	the data transmission between two nodes.
	Valid Values	Usage
	0 or 1	A metric value of 1 is used only on a switch that has more than
		one C-LAN board installed.
		You can always enter either 0 or 1 in the Metric field but the
		choice should be guided by the information below.
	If there are two routes to the same destination, one with metric 0 and one with metric
	1, the switch software will choose the route with metric 0 because it is (if properly
	administered) the more efficient route of the two. On the other hand, if both routes are
	administered with metric 0, the switch will choose whichever it sees first, not
	necessarily the most efficient one.
	By entering 1 in the Metric field, you are telling the switch, “this is a complex route;
	if you know of a simpler route (metric 0) to this destination, use that instead.” In other
	words, metric 1 diverts usage of the route to a metric-0route, if available.
	The following diagram illustrates the use of the Metric field. Switches A and C are
	connected via switch B over two LANs. Switch B has two C-LAN boards, which are
	connected via a ppp link. The network nodes are numbered 1 through 6.

LAN

ethernet

1

C-LANa

Switch A

2C-LAN1

3

ppp

4

C-LAN2

Switch B

5

LAN

ethernet

6

C-LANc

Switch C

The following IP routes are required for communications between switches A and C:

	Administered			Destination		Gateway
Route		on	Board Loc.		Node		Node	Metric
1	Switch A		C-LANa	6		2		0
2	Switch B		C-LAN1	6		4		1
3	Switch B		C-LAN2	1		3		1
4	Switch C		C-LANc	1		5		0
Implied		Switch B	C-LAN2	6		5		0

The implied route from C-LAN2 to node 6 via node 5 is not administered on the IP Routing screen but is a built-in part of the C-LAN firmware and the automatic subnet routing feature. (We are assuming that automatic subnet routing is enabled for node 5 on the Data Module screen.) Therefore, on Switch B there are two routes to destination 6 — route 2 and the implied route.

Administration for Network Connectivity
555-233-504 — Issue 1 — April 2000	CID: 77730	253