5.8 via 155.1.45.4

R4 is standing between BB3 and R5.

Thanks to redistribution on R4,

the routes of BB3,

such as 30.1.0.0 networks can be seen on R5.

 

 

R5# show ip route | include 30

30.0.0.0/8 is variably subnetted, 5 subnets, 2 masks

D EX 30.0.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

D EX 30.1.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

D EX 30.2.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

D EX 30.3.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

D 30.0.0.0/14 [90/2172416] via 155.1.0.4, S0/0/0

 

 

In addition,

interface Serial0/0/0.1 point-to-point

ip summary-address eigrp 100 30.0.0.0 255.252.0.0 5

on R4,

makes the following.

D 30.0.0.0/14 [90/2172416] via 155.1.0.4, Serial0/0/0

 

 

Here is my question.

R5#

D EX 30.0.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

D EX 30.1.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

D EX 30.2.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

D EX 30.3.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

 

Why are they coming via 155.1.45.4?

Not via 155.1.0.4?

 

Comments

  • JoeMJoeM ✭✭✭

    Here is my question.

    R5#

    D EX 30.0.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

    D EX 30.1.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

    D EX 30.2.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

    D EX 30.3.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

     

    Why are they coming via 155.1.45.4?

    Not via 155.1.0.4?

     

    The serial has the best metric for these routes -- over the serial vs the frame-relay.

    The summary-address is coming over the Frame-Relay, because that is where the summary was placed.

     

    EDIT:   run this command.   

             show ip eigrp topology 30.0.0.0 255.255.0.0

  •  

    MG, Joe.

     

    Let me recalculate.

     


     

  • JoeMJoeM ✭✭✭

    Actually the answer is different. 

    I do not have the lab up, but I am betting that the metrics are the same. 

    What happens is the summay-address removes the longer prefixes.  This is the same for the other subnets (31.0.0.0/14)

     

     

  •  

    Let me recalculate and will get back to you, por favor.

  • Here is my question.

    R5#

    D EX 30.0.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

    D EX 30.1.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

    D EX 30.2.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

    D EX 30.3.0.0/16 [170/2172416] via 155.1.45.4, S0/1/0

     

    Why are they coming via 155.1.45.4?

    Not via 155.1.0.4?

     

    You have configured the route summarization on the frame-relay interface s0/0/0.1 but not on the R4's s0/1/0 interface that has point-to-point connection to R5. Specific prefixes are always be preferred over summary route by the routing protocol regardless of whatever the metric or AD is. So, I believe you are running into such an issue for this scenario.

    In order to have a proper test or to verify it, you can configure exact summary route on s0/1/0 of R4 as well. Once you configure it, the metric will be checked & routed accordingly.

    HTH

     

  • JM, 

     

    R5#show ip route | include 30.|31.

         31.0.0.0/8 is variably subnetted, 5 subnets, 2 masks

    D EX    31.3.0.0/16 [170/2172416] via 155.1.0.4, , S0/0/0

    D EX    31.2.0.0/16 [170/2172416] via 155.1.0.4, , S0/0/0

    D EX    31.1.0.0/16 [170/2172416] via 155.1.0.4, , S0/0/0

    D EX    31.0.0.0/16 [170/2172416] via 155.1.0.4, , S0/0/0

    D       31.0.0.0/14 [90/2172416] via 155.1.45.4, , S0/1/0

     

         30.0.0.0/8 is variably subnetted, 5 subnets, 2 masks

    D EX    30.2.0.0/16 [170/2172416] via 155.1.45.4, , S0/1/0

    D EX    30.3.0.0/16 [170/2172416] via 155.1.45.4, , S0/1/0

    D EX    30.0.0.0/16 [170/2172416] via 155.1.45.4, , S0/1/0

    D       30.0.0.0/14 [90/2172416] via 155.1.0.4, , S0/0/0

    D EX    30.1.0.0/16 [170/2172416] via 155.1.45.4, , S0/1/0

     

     

    >What happens is the summay-address removes the longer prefixes.

    >This is the same for the other subnets (31.0.0.0/14)

     

    You mean,

    as for 30.0.0.0/8,

    via 155.1.0.4 was dominated by 30.0.0.0/14.

     

    Therefore, the rest of them have no choice

    but to use via 155.1.45.4?

  • JoeMJoeM ✭✭✭

    Please run the command I posted above.  This will let you know what routes R5 has in its EIGRP Topology Table for that prefix.

     

    The summary-address removes the longer prefixes.

    R5 will choose and use the longer prefixes.....and it will fail-over to the summary-address.

  •  

    I have turned off and on all routers and start from scratch, un moment.

     

    Will get back the result of show ip eigrp topology 30.0.0.0 255.255.0.0

     

  •  

    meanwhile,

     

    Hari,

     

    >You have configured the route summarization on the frame-relay interface s0/0/0.1 but not on the R4's s0/1/0 interface that has point-to-point connection to R5.

    >Specific prefixes are always be preferred over summary route by the routing protocol regardless of whatever the metric or AD is.

     

    Aha.

     

    So the rest of the network,

    that is,

    30.0.0.0

    30.1.0.0

    30.2.0.0

    30.3.0.0

    did not want to use the summary route(via 155.1.0.4).

     

    They prefer non-summary, via 155.1.45.4

    The winner is specific prefixes.

     

    I presume?

     

     

  •  

    R5#show ip eigrp topology 30.0.0.0 255.255.0.0

    please hold, will get back.

  • JoeMJoeM ✭✭✭

    Now if you want to play with this more,  remove the summary-address and then run that command again.

    You should see both routes from the two interfaces (frame and serial).

     

  •  

    R5#show ip eigrp topology 30.0.0.0 255.255.0.0
    IP-EIGRP (AS 100): Topology entry for 30.0.0.0/16
      State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2172416
      Routing Descriptor Blocks:
     

     155.1.45.4 (Serial0/1/0), from 155.1.45.4, Send flag is 0x0
          Composite metric is (2172416/28160), Route is External
          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
          External data:
            Originating router is 150.1.4.4
            AS number of route is 0
            External protocol is RIP, external metric is 1
            Administrator tag is 0 (0x00000000)

      155.1.0.3 (Serial0/0/0), from 155.1.0.3, Send flag is 0x0
          Composite metric is (3201792/2689792), Route is External
          Vector metric:
            Minimum bandwidth is 1544 Kbit
            Total delay is 60310 microseconds
            Reliability is 255/255
            Load is 1/255
            Minimum MTU is 1500
            Hop count is 6
          External data:
            Originating router is 150.1.4.4
            AS number of route is 0
            External protocol is RIP, external metric is 1
            Administrator tag is 0 (0x00000000)
    R5#
    R5#
    R5#

  •  

    R4:

     

    interface Serial0/0/0.1 point-to-point

    no ip summary-address eigrp 100 30.0.0.0 255.252.0.0 5

    !

    interface Serial0/1/0

    no ip summary-address eigrp 100 31.0.0.0 255.252.0.0 5

     

     

     

     

     

     

    R5:

     

    R5#show ip eigrp topology 30.0.0.0 255.255.0.0

    IP-EIGRP (AS 100): Topology entry for 30.0.0.0/16

      State is Passive, Query origin flag is 1, 2 Successor(s), FD is 2172416

      Routing Descriptor Blocks:

     

    155.1.0.4 (Serial0/0/0), from 155.1.0.4, Send flag is 0x0

          Composite metric is (2172416/28160), Route is External

          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

          External data:

            Originating router is 150.1.4.4

            AS number of route is 0

            External protocol is RIP, external metric is 1

            Administrator tag is 0 (0x00000000)

     

    155.1.45.4 (Serial0/1/0), from 155.1.45.4, Send flag is 0x0

          Composite metric is (2172416/28160), Route is External

          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

          External data:

            Originating router is 150.1.4.4

            AS number of route is 0

            External protocol is RIP, external metric is 1

            Administrator tag is 0 (0x00000000)

     

     155.1.0.3 (Serial0/0/0), from 155.1.0.3, Send flag is 0x0

          Composite metric is (3201792/2689792), Route is External

          Vector metric:

            Minimum bandwidth is 1544 Kbit

            Total delay is 60310 microseconds

            Reliability is 255/255

            Load is 1/255

            Minimum MTU is 1500

            Hop count is 6

          External data:

            Originating router is 150.1.4.4

            AS number of route is 0

            External protocol is RIP, external metric is 1

            Administrator tag is 0 (0x00000000)

    R5#

    R5#

    R5#

     

  •  

    They prefer non-summary, via 155.1.45.4

    The winner is specific prefixes.

     

    I presume?

     

    Yes, the specific routes are preferred over the less specific prefixes using longest match rule. For an example, /30 is more specific than /29. So, /30 is always preferred over /29.

    Good luck!

  •  

    Thanks, guys.

     

    It works!

     

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