Loosing EIGRP neighborship

[Randyx]

Hi Guys,

Its me again. Have another question. I have the topology below. I changed the bandwidth on R7's fa1/3 to so the route to R1's 1.1.1.1 will take R7's Fa1/2. But when I shut down R7's fa1/2 supposedly so that the route will tonly ake fa1/3, R7 loses EIGRP neighborship both on R6 and R4, thus leaving R7 without any routes to any network. The connected between R6 to R7 and R4 to R7 are both flapping. They are showing retry limit exceeded error message.

Below are the configs for R3,R4,R6 and R7..Thanks in advance

Current configuration : 1713 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R3
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
no ip icmp rate-limit unreachable
ip cef
!
!
!
!
no ip domain lookup
!
!
!
ip tcp synwait-time 5
!
!
interface FastEthernet0/0
ip address 10.10.34.3 255.255.255.0
speed 100
full-duplex
!
interface Serial0/0
no ip address
shutdown
clock rate 2000000
!
interface FastEthernet0/1
ip address 10.10.36.3 255.255.255.0
speed 100
full-duplex
!
interface Serial0/1
no ip address
shutdown
clock rate 2000000
!
interface Serial0/2
no ip address
shutdown
clock rate 2000000
!
interface Serial0/3
no ip address
shutdown
clock rate 2000000
!
interface FastEthernet1/0
!
interface FastEthernet1/1
no switchport
ip address 10.10.23.3 255.255.255.0
duplex full
speed 100
!
interface FastEthernet1/2
no switchport
ip address 10.10.37.3 255.255.255.0
duplex full
speed 100
!
interface FastEthernet1/3
!
interface FastEthernet1/4
!
interface FastEthernet1/5
!
interface FastEthernet1/6
!
interface FastEthernet1/7
!
interface FastEthernet1/8
!
interface FastEthernet1/9
!
interface FastEthernet1/10
!
interface FastEthernet1/11
!
interface FastEthernet1/12
!
interface FastEthernet1/13
!
interface FastEthernet1/14
!
interface FastEthernet1/15
!
interface Vlan1
no ip address
!
router eigrp 1
network 0.0.0.0
no auto-summary
!
ip forward-protocol nd
!
no ip http server
!
no cdp log mismatch duplex
!
!
!
control-plane
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
line vty 0 4
login
!
end

Current configuration : 1626 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R4
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
no ip icmp rate-limit unreachable
ip cef
!
!
!
!
no ip domain lookup
!
!
!
ip tcp synwait-time 5
!
!
interface FastEthernet0/0
ip address 10.10.34.4 255.255.255.0
speed 100
full-duplex
!
interface Serial0/0
no ip address
shutdown
clock rate 2000000
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/1
no ip address
shutdown
clock rate 2000000
!
interface Serial0/2
no ip address
shutdown
clock rate 2000000
!
interface Serial0/3
no ip address
shutdown
clock rate 2000000
!
interface FastEthernet1/0
!
interface FastEthernet1/1
!
interface FastEthernet1/2
!
interface FastEthernet1/3
!
interface FastEthernet1/4
no switchport
ip address 10.10.47.4 255.255.255.0
duplex full
speed 100
!
interface FastEthernet1/5
!
interface FastEthernet1/6
!
interface FastEthernet1/7
!
interface FastEthernet1/8
!
interface FastEthernet1/9
!
interface FastEthernet1/10
!
interface FastEthernet1/11
!
interface FastEthernet1/12
!
interface FastEthernet1/13
!
interface FastEthernet1/14
!
interface FastEthernet1/15
!
interface Vlan1
no ip address
!
router eigrp 1
network 0.0.0.0
no auto-summary
!
ip forward-protocol nd
!
no ip http server
!
no cdp log mismatch duplex
!
!
!
control-plane
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
line vty 0 4
login
!
end

version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R6
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
no ip icmp rate-limit unreachable
ip cef
!
!
!
!
no ip domain lookup
!
!
!
ip tcp synwait-time 5
!
!
interface FastEthernet0/0
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/0
no ip address
shutdown
clock rate 2000000
!
interface FastEthernet0/1
ip address 10.10.36.6 255.255.255.0
speed 100
full-duplex
!
interface Serial0/1
no ip address
shutdown
clock rate 2000000
!
interface Serial0/2
no ip address
shutdown
clock rate 2000000
!
interface Serial0/3
no ip address
shutdown
clock rate 2000000
!
interface FastEthernet1/0
no switchport
ip address 10.10.26.6 255.255.255.0
duplex full
speed 100
!
interface FastEthernet1/1
!
interface FastEthernet1/2
no switchport
ip address 10.10.56.6 255.255.255.0
duplex full
speed 100
!
interface FastEthernet1/3
no switchport
ip address 10.10.67.6 255.255.255.0
duplex full
speed 100
!
interface FastEthernet1/4
!
interface FastEthernet1/5
!
interface FastEthernet1/6
!
interface FastEthernet1/7
!
interface FastEthernet1/8
!
interface FastEthernet1/9
!
interface FastEthernet1/10
!
interface FastEthernet1/11
!
interface FastEthernet1/12
!
interface FastEthernet1/13
!
interface FastEthernet1/14
!
interface FastEthernet1/15
!
interface Vlan1
no ip address
!
router eigrp 1
network 0.0.0.0
no auto-summary
!
ip forward-protocol nd
!
no ip http server
!
no cdp log mismatch duplex
!
!
!
control-plane
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
line vty 0 4
login
!
end

version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname R7
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
no ip icmp rate-limit unreachable
ip cef
!
!
!
!
no ip domain lookup
!
!
!
ip tcp synwait-time 5
!
!
interface Loopback0
ip address 7.7.7.7 255.255.255.0
!
interface FastEthernet0/0
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/0
no ip address
shutdown
clock rate 2000000
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/1
no ip address
shutdown
clock rate 2000000
!
interface Serial0/2
no ip address
shutdown
clock rate 2000000
!
interface Serial0/3
no ip address
shutdown
clock rate 2000000
!
interface FastEthernet1/0
!
interface FastEthernet1/1
!
interface FastEthernet1/2
no switchport
ip address 10.10.37.7 255.255.255.0
shutdown
duplex full
speed 100
!
interface FastEthernet1/3
no switchport
bandwidth 1000
ip address 10.10.67.7 255.255.255.0
duplex full
speed 100
!
interface FastEthernet1/4
no switchport
ip address 10.10.47.7 255.255.255.0
duplex full
speed 100
!
interface FastEthernet1/5
!
interface FastEthernet1/6
!
interface FastEthernet1/7
!
interface FastEthernet1/8
!
interface FastEthernet1/9
!
interface FastEthernet1/10
!
interface FastEthernet1/11
!
interface FastEthernet1/12
!
interface FastEthernet1/13
!
interface FastEthernet1/14
!
interface FastEthernet1/15
!
interface Vlan1
no ip address
!
router eigrp 1
network 0.0.0.0
no auto-summary
!
ip forward-protocol nd
!
no ip http server
!
no cdp log mismatch duplex
!
!
!
control-plane
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
line vty 0 4
login
!
end

[Georg Pauwen · Accepted solution]

Hello,

I think this is a bug in GNS3 related to the ESW module. I replicated your exact setup with the only difference being that I used GigabitEthernet interfaces. Nothing is flapping, and everything works as you would expect.

Try using onboard interfaces instead of the ESW, and see if the probllem persists.

[Randyx]

I tried it without using the ESW module and it worked fine. Paul Driver is also correct, I should consider the eigrp bandwidth advertisement usage before changing it. 

Thanks guys for the swift response.

[paul driver · Accepted solution]

Hello

I changed the bandwidth on R7's fa1/3 to so the route to R1's 1.1.1.1 will take R7's Fa1/2

Changing the interface Bandwidth CAN cause eigrp adjacency's to flap or not establish - By default eigrp only utilizes 50% of its link bandwidth so if you decrease this then its possible it can negate eigrp packets needed to make these adjacency's

Also beware that changing bw WONT have any impact on path selection in eigrp as its not counted unless it becomes the lowest BW on the entire path. The best approach would be by manipulating the interface Delay as this would be calculated in path selection

Metric = 256*(Bandwidthmin + Delaytotalsum)

res
Paul