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Cisconew
Beginner

GRE tunnel routing issues

Hello all,

I am doing below GRE lab. I am using OSPF for NBMA networks and EIGRP for Tunnel Networks.

But routing table shows both (OSPF/EIGRP) routes for Lan network.

How to solve this?. I have attached the running config for R11 and R31.

 

 

 

2021-10-19 (8).png

R11:

Int Loop 0 :10.1.1.1/24

Int G 0/1 : 172.16.11.1/24

Int Tunnel 100 : 192.168.100.11/24

 

R31:

Int Loop 0 :10.3.3.3/24

Int G 0/2 : 172.16.31.1/24

Int Tunnel 100 : 192.168.100.31/24

 

SP:

 

Int G 0/1 : 172.16.11.2/24

Int G 0/2 : 172.16.31.2/24

 

2021-10-19 (6).png

 

R11#traceroute 10.3.3.3
Type escape sequence to abort.
Tracing the route to 10.3.3.3
VRF info: (vrf in name/id, vrf out name/id)
1 172.16.11.2 2 msec 2 msec 2 msec
2 172.16.31.1 3 msec 2 msec *

 

 

2021-10-19 (7).png

 

1 ACCEPTED SOLUTION

Accepted Solutions
Harold Ritter
Cisco Employee

Hi @Cisconew ,

 

But routing table shows both (OSPF/EIGRP) routes for Lan network.

 

I suppose you mean you receive both ospf and eigrp routes for interface Loopback 0, right?

 

You can go under router ospf and remove the network for the loopback 0 interface. It will then only be received through eigrp.

 

R11:

router ospf 1

no network 10.1.1.1 0.0.0.0 area 0

 

R31:

router ospf 1

no network 10.3.3.3.3 0.0.0.0 area 0

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

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4 REPLIES 4
Georg Pauwen
VIP Expert

Hello,

 

post the full running configs (sh run) of all three routers...

Hi Georg Pauwen,

I have attached the Configs of 3 Routers.

 

pman
Participant

Hi,
Is there a chance you're actually asking why R11 is learning 10.3.3.3/32 via OSPF and 10.3.3.0/24 from EIGRP

and also why does R31 learn 10.1.1.1/32 through OSPF and 10.1.1.0/24 from EIGRP?

 

Or in short, why does OSPF advertise a network that did not exist under interface (loopback configured with /24 while in routing table /32 appears)?

 

so why the ospf doing this?

I guess it's because The loopback interface is always defined as Stub Network Link. By default, the network type of the loopback is P2P, and the 32-bit mask is used. This is why the route learned by the IP address of the loopback interface is the host route of /32 regardless of how long the mask length is configured.RFC2328.png

 

The implementation is based on RFC2328.

Harold Ritter
Cisco Employee

Hi @Cisconew ,

 

But routing table shows both (OSPF/EIGRP) routes for Lan network.

 

I suppose you mean you receive both ospf and eigrp routes for interface Loopback 0, right?

 

You can go under router ospf and remove the network for the loopback 0 interface. It will then only be received through eigrp.

 

R11:

router ospf 1

no network 10.1.1.1 0.0.0.0 area 0

 

R31:

router ospf 1

no network 10.3.3.3.3 0.0.0.0 area 0

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

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