EIGRP Composite Metrics

Bandwidth – is a metric assigned to an interface. Bandwidth describes the transmission speed of an interface. If the bandwidth is not manually entered, EIGRP will assign implicit value to the interface depending on the hardware type. To manually configure the bandwidth, it is done on the interface level and the value is in kilobits.

! The value EIGRP assigned to the fastethernet0/0.
R2#show interface fa0/0
FastEthernet0/0 is up, line protocol is up 
 Hardware is DEC21140, address is ca03.344b.0000 (bia ca03.344b.0000)
 MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100000 usec, 
 reliability 255/255, txload 1/255, rxload 1/255
 ... output omitted for brevity ...
!
! Now, statically lowering the bandwidth of the same interface.
R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#interface fa0/0
R2(config-if)#bandwidth 10000
R2(config-if)#
R2(config-if)#do show interface fa0/0
FastEthernet0/0 is up, line protocol is up 
 Hardware is DEC21140, address is ca03.344b.0000 (bia ca03.344b.0000)
 MTU 1500 bytes, BW 10000 Kbit/sec, DLY 100000 usec, 
 reliability 255/255, txload 1/255, rxload 1/255

When calculating the composite metric to the destination, EIGRP will take the lowest bandwidth value between the router’s interface all the way down to the destination.

Figure 1

Figure 1

Delay – is a metric assigned to an interface. IOS assigns an implicit value depending on the type of hardware. Configuring the delay is done on the interface level using the delay command. Also, this is entered in tens of microseconds. Therefore, if you to configure the delay value of 10000 for an interface you would enter the value in tens of microseconds:

! Delay value before changing its value.
R2#show interface fastethernet0/0
FastEthernet0/0 is up, line protocol is up 
 Hardware is DEC21140, address is ca03.344b.0000 (bia ca03.344b.0000)
 MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec, 
 reliability 255/255, txload 1/255, rxload 1/255
!
! Changing the delay value to 10000.
R2#configure terminal 
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#interface fastethernet0/0
R2(config-if)#delay 1000
R2(config-if)#
R2(config-if)#do show interface fa0/0
FastEthernet0/0 is up, line protocol is up 
 Hardware is DEC21140, address is ca03.344b.0000 (bia ca03.344b.0000)
 MTU 1500 bytes, BW 100000 Kbit/sec, DLY 10000 usec, 
 reliability 255/255, txload 1/255, rxload 1/255

When calculates composite metric to the destination, EIGRP takes the total delay value into account.

Figure 1

Figure 2

Reliability – is dynamically estimated metric of an interface that evaluates the ratio between of the successfully received traffic and all received traffic. The ratio is expressed in decimal number from 1 to 255. 255 is equivalent to 100% reliable whereas 1 is 1% reliable. The calculation is done by comparing the reliability of the advertising neighbor to the destination and the reliability to the reliability to reach the advertising neighbor.

Figure 3

Figure 3

Load– is dynamically calculated metric of an interface that measures the amount of traffic coming through the interface in relation to its capacity.

Maximum Transition Unit (MTU) – EIGRP does not use MTU to be part of its metric calculation even though EIGRP advertise the MTU along the path.

Hop Count – this is also not used in metric calculation. The hop count is simply used as a last resort security measure for potential loops. The default value is 100, and it can be modify from 1 to 255. To configure the hop count, this is done under the EIGRP router config mode.

R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#router eigrp 1
R2(config-router)#metric maximum-hops 150
R2(config-router)#
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About networkshinobi

This blog is about the things I learned about computers and networking to help me to remember them as I push further my studies. I created this blog to help myself to continue my education; and if you find this blog helpful for your studies, that is great. That is one of the reasons why I made this blog, to share my interest and knowledge. Also, all the entries/posts I made are based on my views, opinion and for educational purposes only. If you see some mistakes, feel free to drop some comments. I would appreciate all the helpful comments. Thanks BTC: 14wVPFBWNAKmfNsgUrPpw8EytkXFLjxYoU ETH: 0x8528793dF77a57186f5B15dA6DC1eaA3c5e92c4a LTC : LMpW2rGYnYdUwvnHA4huB6TGcPEEc1JzXw
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