variance and max paths...

variance will allow you to put unequal routes into the route table by making them near equal... max paths can be used to limit that amount...

from router 2's perspective, it doesn't take an astronaut to figure out which route will be best... the more bandwidth, the lower metric...

r2(config-router)#do sh ip eigrp topo 172.18.1.0/24
EIGRP-IPv4 Topology Entry for AS(1)/ID(172.20.10.1) for 172.18.1.0/24
  State is Passive, Query origin flag is 1, 2 Successor(s), FD is 3139840
  Descriptor Blocks:
  172.20.15.14 (Serial2/1), from 172.20.15.14, Send flag is 0x0
      Composite metric is (3139840/128256), route is Internal
      Vector metric:
        Minimum bandwidth is 1024 Kbit
        Total delay is 25000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
        Originating router is 172.18.1.1
  172.20.15.18 (Serial2/2), from 172.20.15.18, Send flag is 0x0
      Composite metric is (5639936/128256), route is Internal
      Vector metric:
        Minimum bandwidth is 512 Kbit
        Total delay is 25000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
        Originating router is 172.18.1.1
  172.20.15.22 (Serial2/3), from 172.20.15.22, Send flag is 0x0
      Composite metric is (20640000/128256), route is Internal
      Vector metric:
        Minimum bandwidth is 128 Kbit
        Total delay is 25000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
        Originating router is 172.18.1.1

if we wanted all three in the route table, divide the largest by the smallest to get the variance... 3 goes into 20 almost 7 times... variance would be 7 to get them all near equal...2 could get the two best in...


without variance i can get 1 in...

r2(config-router)#do sh ip route eigrp 

Gateway of last resort is not set

      172.18.0.0/24 is subnetted, 1 subnets
D        172.18.1.0 [90/3139840] via 172.20.15.14, 00:04:02, Serial2/1
D     192.168.16.0/24 [90/20640000] via 172.20.15.2, 00:04:02, Serial1/0
D     192.168.17.0/24 [90/2297856] via 172.20.15.6, 00:04:02, Serial1/2

2 will get the best 2 in because 3 goes into 5.6 almost 2 times

r2(config-router)#var 2
r2(config-router)#do sh ip route eigrp

Gateway of last resort is not set

      172.18.0.0/24 is subnetted, 1 subnets
D        172.18.1.0 [90/5639936] via 172.20.15.18, 00:03:04, Serial2/2
                    [90/3139840] via 172.20.15.14, 00:03:04, Serial2/1

6 won't work because 20 divided by 3 is closer to 7...

r2(config-router)#var 6
r2(config-router)#do sh ip route eigrp

Gateway of last resort is not set

      172.18.0.0/24 is subnetted, 1 subnets
D        172.18.1.0 [90/5639936] via 172.20.15.18, 00:00:03, Serial2/2
                    [90/3139840] via 172.20.15.14, 00:00:03, Serial2/1

yeah, 6 is a loser...

r2(config-router)#var 7
r2(config-router)#do sh ip route eigrp

Gateway of last resort is not set

      172.18.0.0/24 is subnetted, 1 subnets
D        172.18.1.0 [90/20640000] via 172.20.15.22, 00:00:03, Serial2/3
                    [90/5639936] via 172.20.15.18, 00:00:03, Serial2/2
                    [90/3139840] via 172.20.15.14, 00:00:03, Serial2/1

we got them all in now...

but we want to go back to 1, while keeping our variance options open...

r2(config-router)#maximum-paths 1
r2(config-router)#do sh ip route eigrp

Gateway of last resort is not set

      172.18.0.0/24 is subnetted, 1 subnets
D        172.18.1.0 [90/3139840] via 172.20.15.14, 00:00:04, Serial2/1
D     192.168.16.0/24 [90/20640000] via 172.20.15.2, 00:00:04, Serial1/0
D     192.168.17.0/24 [90/2297856] via 172.20.15.6, 00:00:04, Serial1/2

if we put all 3 in and kill a link, what happens...

r2(config-router)#no max 1
r2(config-router)#do sh ip route eigrp

Gateway of last resort is not set

      172.18.0.0/24 is subnetted, 1 subnets
D        172.18.1.0 [90/20640000] via 172.20.15.22, 00:00:03, Serial2/3
                    [90/5639936] via 172.20.15.18, 00:00:03, Serial2/2
                    [90/3139840] via 172.20.15.14, 00:00:03, Serial2/1
D     192.168.16.0/24 [90/20640000] via 172.20.15.2, 00:00:03, Serial1/0
D     192.168.17.0/24 [90/6663936] via 172.20.15.18, 00:00:03, Serial2/2
                      [90/10639872] via 172.20.15.10, 00:00:03, Serial1/1
                      [90/2297856] via 172.20.15.6, 00:00:03, Serial1/2
r2(config-router)#int s2/2
r2(config-if)#shut
r2(config-if)#int s2/2
*Sep 11 19:36:35: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 172.20.15.18 (Serial2/2) is down: interface down
r2(config-if)#int s2/2
*Sep 11 19:36:37: %LINK-5-CHANGED: Interface Serial2/2, changed state to administratively down
*Sep 11 19:36:38: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial2/2, changed state to down
r2(config-if)#do sh ip route eigrp

Gateway of last resort is not set

      172.18.0.0/24 is subnetted, 1 subnets
D        172.18.1.0 [90/20640000] via 172.20.15.22, 00:00:07, Serial2/3
                    [90/3139840] via 172.20.15.14, 00:00:07, Serial2/1
      172.20.0.0/16 is variably subnetted, 13 subnets, 3 masks
D        172.20.15.16/30 [90/21024000] via 172.20.15.22, 00:00:06, Serial2/3
                         [90/6023936] via 172.20.15.14, 00:00:06, Serial2/1
D     192.168.16.0/24 [90/20640000] via 172.20.15.2, 00:00:30, Serial1/0
D     192.168.17.0/24 [90/10639872] via 172.20.15.10, 00:00:07, Serial1/1
                      [90/2297856] via 172.20.15.6, 00:00:07, Serial1/2

duh...

you can get the same result by multiplying the lower number by x to get to the higher number... somehow dividing makes more sense to me...