Solved: Re: EIGRP - missing path

hubertzw · ‎11-07-2017

Hi,

I'm trying to understand why I can't see secondary path in one of following case scenarios:

a)fa0/0-> delay 100, variance 1:

P 10.10.3.0/24, 1 successors, FD is 158720
        via 172.16.3.3 (158720/156160), FastEthernet1/1
        via 172.16.1.2 (179200/128256), FastEthernet0/0

R1#sh ip route 10.10.3.0
Routing entry for 10.10.3.0/24
  Known via "eigrp 100", distance 90, metric 158720, type internal
  Redistributing via eigrp 100
  Last update from 172.16.3.3 on FastEthernet1/1, 00:01:34 ago
  Routing Descriptor Blocks:
  * 172.16.3.3, from 172.16.3.3, 00:01:34 ago, via FastEthernet1/1
      Route metric is 158720, traffic share count is 1
      Total delay is 5200 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2
R1#

b)fa0/0->no delay, variance 1:

P 10.10.3.0/24, 1 successors, FD is 156160
        via 172.16.1.2 (156160/128256), FastEthernet0/0

R1#sh ip route 10.10.3.0
Routing entry for 10.10.3.0/24
  Known via "eigrp 100", distance 90, metric 156160, type internal
  Redistributing via eigrp 100
  Last update from 172.16.1.2 on FastEthernet0/0, 00:00:30 ago
  Routing Descriptor Blocks:
  * 172.16.1.2, from 172.16.1.2, 00:00:30 ago, via FastEthernet0/0
      Route metric is 156160, traffic share count is 1
      Total delay is 5100 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1
R1#

c)fa0/0-> delay 100, variance 2:

P 10.10.3.0/24, 2 successors, FD is 179200
        via 172.16.1.2 (179200/128256), FastEthernet0/0
        via 172.16.3.3 (158720/156160), FastEthernet1/1

R1#sh ip route 10.10.3.0
Routing entry for 10.10.3.0/24
  Known via "eigrp 100", distance 90, metric 158720, type internal
  Redistributing via eigrp 100
  Last update from 172.16.3.3 on FastEthernet1/1, 00:01:54 ago
  Routing Descriptor Blocks:
    172.16.3.3, from 172.16.3.3, 00:01:54 ago, via FastEthernet1/1
      Route metric is 158720, traffic share count is 80
      Total delay is 5200 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2
  * 172.16.1.2, from 172.16.1.2, 00:01:54 ago, via FastEthernet0/0
      Route metric is 179200, traffic share count is 71
      Total delay is 6000 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1
R1#

d)fa0/0->no delay, variance 2:

P 10.10.3.0/24, 2 successors, FD is 156160, serno 121
        via 172.16.1.2 (156160/128256), FastEthernet0/0
        via 172.16.3.3 (158720/156160), FastEthernet1/1

R1#sh ip route 10.10.3.0
Routing entry for 10.10.3.0/24
  Known via "eigrp 100", distance 90, metric 156160, type internal
  Redistributing via eigrp 100
  Last update from 172.16.3.3 on FastEthernet1/1, 00:00:46 ago
  Routing Descriptor Blocks:
    172.16.3.3, from 172.16.3.3, 00:00:46 ago, via FastEthernet1/1
      Route metric is 158720, traffic share count is 59
      Total delay is 5200 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2
  * 172.16.1.2, from 172.16.1.2, 00:00:46 ago, via FastEthernet0/0
      Route metric is 156160, traffic share count is 60
      Total delay is 5100 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1
R1#

In a scenario A I see two available paths in topology table and one of them is successor, why I can't see the same number of paths in scenario B?

IMO I should see also the path available via Fa1/1 (172.16.3.3) with a metric: 158720/156160 and 1 successor over Fa0/0.

Thanks

hubertzw · ‎11-11-2017

I found the error is a bug. When I changed IOS version the second route is not taken to topology table:

R1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#router eigrp 100
R1(config-router)#no variance
...
*Nov 11 23:22:38.043: DUAL: Find FS for dest 10.10.3.0/24. FD is 156160, RD is 156160
*Nov 11 23:22:38.043: DUAL:     172.16.1.2 metric 156160/128256
*Nov 11 23:22:38.043: DUAL:     172.16.3.3 metric 158720/156160 found Dmin is 156160
*Nov 11 23:22:38.043: DUAL: RT installed 10.10.3.0/24 via 172.16.1.2
...


R1(config-router)#va
R1(config-router)#variance 2
R1(config-router)#
..
*Nov 11 23:24:37.723: DUAL: Find FS for dest 10.10.3.0/24. FD is 156160, RD is 156160
*Nov 11 23:24:37.727: DUAL:     172.16.1.2 metric 156160/128256
*Nov 11 23:24:37.727: DUAL:     172.16.3.3 metric 158720/156160 found Dmin is 156160
*Nov 11 23:24:37.727: DUAL: RT installed 10.10.3.0/24 via 172.16.1.2

View solution in original post

hubertzw · ‎11-07-2017

ok, I found the reason, with 'all-links' I can see both:

R1#sh ip eigrp topo all-links
...
P 10.10.3.0/24, 1 successors, FD is 156160, serno 140
        via 172.16.1.2 (156160/128256), FastEthernet0/0
        via 172.16.3.3 (158720/156160), FastEthernet1/1

Weird I don't need this parameter for scenario A .

hubertzw · ‎11-07-2017

eh, I found the reason: feasibility condition, sorry for spam but I didn't know how to remove posts

DP20 · ‎11-07-2017

The command, Sh ip eigrp topology all-links, shows all eigrp routes, including the ones that don't meet the feasibility condition.
A route can only be a feasible successor(backup), if its reported distance is less than the current successor's feasible distance.

Variance only applies to routes that meet the above feasibility condition, although I'm a bit perplexed because Scenario D clearly contradicts the feasibility condition.

What happens when you change the variance back to 1 for Scenario D?

hubertzw · ‎11-07-2017

It's basically scenario B again:

R1#sh ip eigrp topology
EIGRP-IPv4 Topology Table for AS(100)/ID(10.10.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

...
P 10.10.3.0/24, 1 successors, FD is 156160
        via 172.16.1.2 (156160/128256), FastEthernet0/0

R1#

R1#sh ip eigrp topology all-links
EIGRP-IPv4 Topology Table for AS(100)/ID(10.10.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

...
P 10.10.3.0/24, 1 successors, FD is 156160, serno 153
        via 172.16.1.2 (156160/128256), FastEthernet0/0
        via 172.16.3.3 (158720/156160), FastEthernet1/1

R1#

So, by the definition FD(156160) of 172.16.1.2 is not higher than RD(156160) of 172.16.3.3. They are the same and it's clear why I can't see path via 172.16.3.3. Not sure why I can see two with 'variance 2':

R1(config)#router ei
R1(config)#router eigrp 100
R1(config-router)#va
R1(config-router)#variance 2
R1(config-router)#
...
*Nov  7 16:52:45.930: EIGRP-IPv4(100): Find FS for dest 10.10.3.0/24. FD is 156160, RD is 156160 on tid 0
*Nov  7 16:52:4
R1(config-router)#5.930: EIGRP-IPv4(100):       172.16.1.2 metric 156160/128256
*Nov  7 16:52:45.930: EIGRP-IPv4(100):  172.16.3.3 metric 158720/156160 found Dmin is 156160
*Nov  7 16:52:45.930: DUAL: AS(100) RT installed 10.10.3.0/24 via 172.16.1.2
*Nov  7 16:52:45.930: DUAL: AS(100) RT installed 10.10.3.0/24 via 172.16.3.3
*Nov  7 16:52:45.930: DUAL: AS(100) Send update about 10.10.3.0/24. Reason: new if on tid 0
R1(config-router)#

R1(config-router)#no variance
R1(config-router)#
...
*Nov  7 16:55:46.526: EIGRP-IPv4(100): Find FS for dest 10.10.3.0/24. FD is 156160, RD is 156160 on tid 0
*Nov  7 16:55:46.526: EIGRP-IPv4(100):  172.16.1.2 metric 156160/128256
*Nov  7 16:55:46.526: EIGRP-IPv4(100):  172.16.3.3 metric 158720/156160 found Dmin is 156160
*Nov  7 16:55:4
R1(config-router)#6.526: DUAL: AS(100) RT installed 10.10.3.0/24 via 172.16.1.2
*Nov  7 16:55:46.526: DUAL: AS(100) Send update about 10.10.3.0/24. Reason: lost if on tid 0
R1(config-router)#

It looks like the variance is taken into feasible condition check:

variance 1:

172.16.1.2 metric 156160/128256 <- installed

172.16.3.3 metric 158720/156160 found Dmin is 156160 <- removed (expected)

variance 2:

172.16.1.2 metric 156160/128256 <- installed

172.16.3.3 metric 158720/156160 found Dmin is 156160 <- installed (why?)

hubertzw · ‎11-11-2017

I found the error is a bug. When I changed IOS version the second route is not taken to topology table:

R1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#router eigrp 100
R1(config-router)#no variance
...
*Nov 11 23:22:38.043: DUAL: Find FS for dest 10.10.3.0/24. FD is 156160, RD is 156160
*Nov 11 23:22:38.043: DUAL:     172.16.1.2 metric 156160/128256
*Nov 11 23:22:38.043: DUAL:     172.16.3.3 metric 158720/156160 found Dmin is 156160
*Nov 11 23:22:38.043: DUAL: RT installed 10.10.3.0/24 via 172.16.1.2
...


R1(config-router)#va
R1(config-router)#variance 2
R1(config-router)#
..
*Nov 11 23:24:37.723: DUAL: Find FS for dest 10.10.3.0/24. FD is 156160, RD is 156160
*Nov 11 23:24:37.727: DUAL:     172.16.1.2 metric 156160/128256
*Nov 11 23:24:37.727: DUAL:     172.16.3.3 metric 158720/156160 found Dmin is 156160
*Nov 11 23:24:37.727: DUAL: RT installed 10.10.3.0/24 via 172.16.1.2