eigrp - Could not ping between routers

[BlobBalls75605]

   Hi, I'm new to the networking academy. I've tried to get the 'triangle routers' to ping each other but not as intended to be succeeded. Is there any problem with my configuration? 

Router 1

en
config t
int fa0/0
ip add 172.16.1.1 255.255.255.0
no shutdown
exit
int s0/0
ip add 172.16.3.1 255.255.255.252
no shutdown
clock rate 64000
exit
int s0/1
ip add 192.168.10.5 255.255.255.252
no shutdown
exit
router eigrp 10
network 172.16.1.0 0.0.0.255
network 172.16.3.0 0.0.0.3
network 192.168.10.4 0.0.0.3
exit
exit
copy run start

Router 2

en
config t
int fa0/0
ip add 172.16.2.1 255.255.255.0
no shutdown
exit
int s0/0
ip add 192.168.10.9 255.255.255.252
no shutdown
clock rate 64000
exit
int s0/1
ip add 172.16.3.2 255.255.255.252
no shutdown
exit
router eigrp 10
network 172.16.2.0 0.0.0.255
network 192.168.10.8 0.0.0.3
network 172.16.3.1 0.0.0.3
exit
exit
copy run start

Router 3
en
config t
int fa0/0
ip add 192.168.1.1 255.255.255.0
no shutdown
exit
int s0/0
ip add 192.168.10.6 255.255.255.252
no shutdown
clock rate 64000
exit
int s0/1
ip add 192.168.10.10 255.255.255.252
no shutdown
exit
router eigrp 10
network 192.168.1.0 0.0.0.255
network 192.168.10.5 0.0.0.3
network 192.168.10.9 0.0.0.3
exit
exit
copy run start

[Francesco Molino]

Hi

Based on the design we see links between all 3 routers forming a triangle.
On all routers, under router eigrp section, add no auto-summary.

On R2, remove network 172.16.3.1 0.0.0.3 and replace it by network 172.16.3.0 0.0.0.3
On R3, remove the following lines under router eigrp section:
network 192.168.10.5 0.0.0.3
network 192.168.10.9 0.0.0.3
And replace them by:
network 192.168.10.4 0.0.0.3
network 192.168.10.8 0.0.0.3


Once you've done that, please share the output of show ip eigrp neighbor and show ip route for each routers.
Please put these outputs in a text file.

[Giuseppe Larosa]

Hello @BlobBalls75605 ,

@Francesco Molino  is right

you are facing one of the legacy aspects of EIGRP protocol the automatic auto summary at major network boundary.

The major networks are those determined by the most significant = rightmost octet in an IPv4 address.

So 192.168.0.0/24 are class C up to 223.255.255.0/24  Class C major network  254 hosts

128.0.0.0/16 to 191.255.0.0/16 are Class B major network 65,5534 hosts

127.0.0.0/8  reserved for loopback addresses and for internal communication between router processors and linecars (seen this in use in Cisco 12000 an ancestor or current CSR)

1.0.0.0/8 to 126.0.0.0/8 are Class A

These major networks existed because the first routing protocols like RIPv1 and IGRP were not able to carry the subnet mask and allowed only the Fixed Length Subnet Mask FLSM meaning that all links should have the same subnet mask within a single major network.

EIGRP has been created from IGRP and has the following properties:

EIGRP is able to carry the subnet mask so it support VLSM so we can use /30 subnets on serial links instead of wasting a /24 just to make an example. V= Variable.

All current routing protocols RIPv2, EIGRP, OSPF, IS-IS and  BGP carry the subnet mask and are called classless routing protocols.

EIGRP by default summarizes to major network when sending an EIGRP update out of an interface with an IP address belonging to a different major network.

So R1 should see routes for the R2 and R3 LAN subnets as 172.16.0.0/16 and 192.168.1.0/24 respectively but this should not create connectivity problems (until there is no major network partitioned )

From the point of view of R3 both R1 and R2 are providing a path to 172.16.0.0/16 and this is  the cause of your conectivty issues.

Major network 172.16.0.0/16 is partitioned with subnet 172.16.1.0/24 behind R1 and subnet 172.16.2.0/24 behind R2.

Hope to help

Giuseppe

[Richard Burts]

We have had a couple of helpful posts explaining the issues about auto summarization. But there is a more fundamental problem that is impacting connectivity. According to the diagram and the posted configs we have these addresses on the serial links connecting the routers:

R1 S0/0 172.16.3.1/30 to R3 S0/1 192.168.10.10/30 

R1 S0/1 192.168.10.5/30 to R2 S0/0 192.168.10.9/30

R2 S0/1 172.16.3.2/30 to R3 S0/0 192.168.10.6/30

None of these have a peer in the same subnet and several of them the peer is not even in the same major network. Running EIGRP on these interfaces would not form any neighbor relationships because of the mismatch in addressing.