Bouncy traceroute on OSPF Frame Relay.

Michael Douville · ‎01-09-2017

I cannot seem to figure how to add pictures to this forum so I apologize beforehand. I did include a attached screenshot.

Frame Relay setup:

R1/R2/R3:

172.12.123.0/24

R1 <----------------> R2

R1 <----------------> R3

Rest of network.

Fast ethernet connection between R1 and R5

R1/R5:

30.1.1.0/24 (R1 - .1, R5 - .5)

R2 R3 and R4 are also connected to SWT1. With the following network:

R2/R3/R4:

172.12.234.0/24 (R2 - .2, R3 - .3, R4 - .4)

There is a loopback on R4 of 4.4.4.4 that we are doing a traceroute to.

There is a routemap involved but i don't believe it is influencing my question.

The following are the configs:

*************** R1 ****************

hostname R1
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
no ip icmp rate-limit unreachable
ip cef
!
!
interface Loopback1
ip address 1.1.1.1 255.255.255.0
!
interface Loopback15
ip address 15.1.1.1 255.255.255.0
!
interface Loopback50
ip address 50.1.1.1 255.255.255.0
!
interface FastEthernet0/0
ip address 30.1.1.1 255.255.255.0
ip policy route-map NEXTHOP
duplex auto
speed auto
!
interface Serial0/0
description "frame-relay inverse-arp" is default
ip address 172.12.123.1 255.255.255.0
encapsulation frame-relay
clock rate 64000
frame-relay map ip 172.12.123.2 102 broadcast
frame-relay map ip 172.12.123.3 103 broadcast
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/1
no ip address
clock rate 2000000
!
router ospf 1
log-adjacency-changes
redistribute connected subnets
network 1.1.1.0 0.0.0.255 area 0
network 15.1.1.0 0.0.0.255 area 0
network 30.1.1.0 0.0.0.255 area 0
network 50.1.1.0 0.0.0.255 area 0
network 172.12.123.0 0.0.0.255 area 0
neighbor 172.12.123.2
neighbor 172.12.123.3
!
ip forward-protocol nd
!
!
no ip http server
no ip http secure-server
!
access-list 105 permit ip host 30.1.1.5 host 4.4.4.4
!
route-map NEXTHOP permit 10
match ip address 105
set ip next-hop 172.12.123.3
!

*************** R2 ****************

hostname R2
!
!
interface FastEthernet0/0
ip address 172.12.234.2 255.255.255.0
duplex auto
speed auto
!
interface Serial0/0
ip address 172.12.123.2 255.255.255.0
encapsulation frame-relay
ip ospf priority 0
clock rate 64000
frame-relay map ip 172.12.123.1 201 broadcast
frame-relay map ip 172.12.123.3 201 broadcast
no frame-relay inverse-arp
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/1
no ip address
clock rate 2000000
!
router ospf 1
log-adjacency-changes
network 172.12.123.0 0.0.0.255 area 0
network 172.12.234.0 0.0.0.255 area 0
!

*************** R3 ****************

hostname R3
!
!
interface FastEthernet0/0
ip address 172.12.234.3 255.255.255.0
duplex auto
speed auto
!
interface Serial0/0
ip address 172.12.123.3 255.255.255.0
encapsulation frame-relay
ip ospf priority 0
clock rate 64000
frame-relay map ip 172.12.123.1 301 broadcast
frame-relay map ip 172.12.123.2 301 broadcast
no frame-relay inverse-arp
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
interface Serial0/1
no ip address
clock rate 2000000
!
router ospf 1
log-adjacency-changes
network 172.12.123.0 0.0.0.255 area 0
network 172.12.234.0 0.0.0.255 area 0
!

*************** R4 ****************

interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
interface FastEthernet0/0
ip address 172.12.234.4 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
!
router ospf 1
log-adjacency-changes
network 4.4.4.0 0.0.0.255 area 0
network 172.12.234.0 0.0.0.255 area 0

This is a Lab from Chris Bryants CCNP route course and I cannot get the output that he gets. On R1 he does the following trace route and gets this output:

#traceroute 4.4.4.4 source 1.1.1.1

1 172.12.123.2

2. 172.12.234.4

When I do this I get the following:

R1#traceroute 4.4.4.4 source 1.1.1.1

Type escape sequence to abort.
Tracing the route to 4.4.4.4

1 172.12.123.3 40 msec
172.12.123.2 40 msec
172.12.123.3 0 msec
2 172.12.234.4 16 msec 24 msec 24 msec

As you can see bouncy bouncy between 123.2 and 123.3 be fore it figures where to go. Here is the OSPF route:

R1#sh ip route ospf
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/75] via 172.12.123.3, 01:02:45, Serial0/0
[110/75] via 172.12.123.2, 01:02:45, Serial0/0
172.12.0.0/24 is subnetted, 2 subnets
O 172.12.234.0 [110/74] via 172.12.123.3, 01:02:45, Serial0/0
[110/74] via 172.12.123.2, 01:02:45, Serial0/0

I see how I have an equal cost going to both sides, is this causing it? How come he isn't?

Thanks very much in advance!!

chrihussey · ‎01-09-2017

I don't think it is bouncing between the two while trying to figure out where to go. The first hop has two equal cost paths and it is choosing one, then the other, then the first again in a normal load sharing fashion. This is expected behavior.

The second hop is a single route which is why there is only one IP there. If you'll notice there is a response time after each first hop try and for the second hop, there are three response times. When you do a trace route it essentially tries it three times. Hope this makes sense.

Michael Douville · ‎01-10-2017

It still confuses me because of his results. One thing I didn't say was that Chris does not have a switch in the lab. But to me its impossible not to have one. In his version R2 and R3 are directly connected to R4! But how is that even possible since you cannot have overlapping ip's from the same subnet. I attached a picture of his lab. Sorry I didn't mean to mislead, but that was the only way in my mind to make it work. But maybe I'm missing something here as well? I have attached the picture of his network.

Thanks!

Mike

chrihussey · ‎01-10-2017

It has been forever since I did it but you can set up a router to be a frame relay switch. That's what appears to be going on and the routing you ask about is occurring across the frame relay cloud.

http://www.ciscopress.com/articles/article.asp?p=170741&seqNum=7

Michael Douville · ‎01-11-2017

Thanks Chris,

I'm thinking this may be something with GNS3, gonna try different versions of the router. Thanks for your answers!