위의 그림에서 B1과 WAN1이 Neighbor가 될때 FD의 Metric을 구해보자
Metric = 256 * ((10,000,000 / slowest-bandwidth) + cumulative-delay)
An example certainly helps in this case. Figure 3-5 repeats some information about the
topology exchange process between Routers B1 and WAN1 (refer to Figure 3-1), essentially
showing the metric components as sent by B1 to WAN1 (Step 1)
The metric components from WAN1’s perspective (Step 2).
Steps 3 and 4 in Figure 3-5 show WAN1’s calculation of the RD and FD for 10.11.1.0/24, respectively.
Router WAN1 takes the metric components as received from B1, and plugs them into the formula, to calculate the RD, which is the same integer metric that Router B1 would have calculated as its FD.
Step 4 shows the same formula but with the metric components as listed at Step 2–after the adjustments made on WAN1.
Step 4 shows WAN1’s FD calculation, which is much larger due to the much lower constraining bandwidth
plus the much larger cumulative delay.
WAN1 chooses its best route to reach 10.11.1.0/24 based on the lowest FD among all possible routes.
Looking back to the much more detailed Figure 3-1, presumably a couple of
other routes might have been possible, but WAN1 happens to choose the route shown in
Figure 3-5 as its best route. As a result, WAN1’s show ip route command lists the FD calculated
in Figure 3-5 as the metric for this route, as shown in Example 3-4.
WAN1#show ip eigrp topo 10.11.1.0/24
IP-EIGRP (AS 1): Topology entry for 10.11.1.0/24
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2172416
Routing Descriptor Blocks:
10.1.1.2 (Serial0/0/0.1), from 10.1.1.2, Send flag is 0x0
Composite metric is (2172416/28160), Route is Internal
Vector metric:
Minimum bandwidth is 1544 Kbit
Total delay is 20100 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 1
10.9.1.2 (FastEthernet0/0), from 10.9.1.2, Send flag is 0x0
Composite metric is (2174976/2172416), Route is Internal
Vector metric:
Minimum bandwidth is 1544 Kbit
Total delay is 20200 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 2
WAN1#show ip route 10.11.1.0
Routing entry for 10.11.1.0/24
Known via “eigrp 1”, distance 90, metric 2172416, type internal
Redistributing via eigrp 1
Last update from 10.1.1.2 on Serial0/0/0.1, 00:02:42 ago
Routing Descriptor Blocks:
* 10.1.1.2, from 10.1.1.2, 00:02:42 ago, via Serial0/0/0.1
Route metric is 2172416, traffic share count is 1
Total delay is 20100 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
!
! Below, the route for 10.11.1.0/24 is again listed, with the metric (FD), and
! the same next-hop and outgoing interface information.
!
WAN1#show ip route eigrp
10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
D 10.11.1.0/24 [90/2172416] via 10.1.1.2, 00:10:40, Serial0/0/0.1
D 10.12.1.0/24 [90/2172416] via 10.1.1.6, 00:10:40, Serial0/0/0.2
D 10.1.2.0/30 [90/2172416] via 10.9.1.2, 00:10:40, FastEthernet0/0
D 10.1.2.4/30 [90/2172416] via 10.9.1.2, 00:10:40, FastEthernet0/0
| Interface Type | Bandwidth (Kbps) | Delay (Microseconds) |
| Serial | 1544 | 2000 |
| GigE | 1,000,000 | 10 |
| FastE | 100,000 | 100 |
| Ethernet | 10,000 | 1000 |
이는 몇몇 인터페이스에 대한 bandwidth와 delay의 default value이다.
