passive-interface Loopback0 on OPSF

solemdoms5 · ‎12-24-2012

I thought the I/F that passive-interface is configured do not send their routing update to other routers .

If the routing protocol was OSPF(and EIGRP) , the I/F dont send HELLO packet too .so the neighboring relationship would be dead

This is my understanding of passive-interface .

but In my labo (GNS3), Routers know the network that passive-interface is configured.

I just want to know why is that ?

Is my understanding wrong ?

Here is configuration :

R4

interface Loopback0

ip address 172.16.255.4 255.255.255.255 　●

router ospf 1

log-adjacency-changes

passive-interface Loopback0 ●

R5#sh ip route ospf

172.16.0.0/16 is variably subnetted, 8 subnets, 5 masks

O 172.16.255.2/32 [110/2] via 172.16.2.2, 00:19:58, FastEthernet0/0

O 172.16.255.1/32 [110/66] via 172.16.2.2, 00:19:58, FastEthernet0/0

O 172.16.255.4/32 [110/130] via 172.16.2.2, 00:19:58, FastEthernet0/0　●

O 172.16.1.0/26 [110/66] via 172.16.2.2, 00:19:58, FastEthernet0/0

O 172.16.1.124/30 [110/129] via 172.16.2.2, 00:19:58, FastEthernet0/0

O 172.16.100.0/29 [110/65] via 172.16.2.2, 00:19:58, FastEthernet0/0

Please　refer to the topology map attached .

Regards.

Abzal · ‎12-24-2012

Hi,

Passive interface means that it will not send hello messages to neighbor. But you can be advertising this subnet.
Can you post the output

On R4:

sh run | sec router ospf

On R5:

sh ip ospf network 172.16.255.4

Hope it will help.

Sent from Cisco Technical Support iPhone App

Best regards,
Abzal

solemdoms5 · ‎12-24-2012

Thank you for reply .

On R4:

sh run | sec router ospf

Is this correct command ? it doesnt work in my labo.

sh ip ospf network 172.16.255.4

you mean neighbor ?if so , there is blank .

R5#sh ip ospf neighbor 172.16.255.4

R5#

Regards .

Abzal · ‎12-24-2012

Ok, I see

Then show output

On R4:

sh run

On R5:

sh ip ospf database

Abzal

Best regards,
Abzal

solemdoms5 · ‎12-24-2012

Here you are .

R4#sh run

Building configuration...

Current configuration : 1539 bytes

!

version 12.3

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

ip subnet-zero

!

ip cef

no ip domain lookup

ip domain name lab.local

!

ip audit po max-events 100

!

interface Loopback0

ip address 172.16.255.4 255.255.255.255

!

interface Loopback1

ip address 172.16.1.193 255.255.255.252

!

interface Loopback2

ip address 172.16.1.225 255.255.255.224

!

interface Loopback100

ip address 1.1.1.1 255.255.255.255

!

interface FastEthernet0/0

no ip address

shutdown

duplex auto

speed auto

!

interface FastEthernet0/1

no ip address

shutdown

duplex auto

speed auto

!

interface Serial1/0

ip address 172.16.1.126 255.255.255.252

encapsulation ppp

serial restart-delay 0

clock rate 128000

!

interface Serial1/1

no ip address

shutdown

serial restart-delay 0

!

interface Serial1/2

no ip address

shutdown

serial restart-delay 0

!

interface Serial1/3

no ip address

shutdown

serial restart-delay 0

!

router ospf 1

log-adjacency-changes

passive-interface FastEthernet0/0

passive-interface Loopback0

network 172.16.1.124 0.0.0.3 area 0

network 172.16.1.160 0.0.0.31 area 0

network 172.16.255.4 0.0.0.0 area 0

!

no ip http server

no ip http secure-server

ip classless

!

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

!

R5#sh ip ospf database

OSPF Router with ID (172.16.255.5) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count

172.16.255.1 172.16.255.1 412 0x80000007 0x0046B7 5

172.16.255.2 172.16.255.2 196 0x80000008 0x00E9DE 3

172.16.255.3 172.16.255.3 369 0x80000008 0x00CFC4 3

172.16.255.4 172.16.255.4 106 0x80000005 0x001CFF 3

172.16.255.5 172.16.255.5 35 0x80000006 0x0088CA 2

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum

172.16.2.2 172.16.255.2 196 0x80000005 0x004E07

172.16.100.1 172.16.255.1 412 0x80000006 0x00DB40

Abzal · ‎12-24-2012

Hi,

Here is you can see altough it is passive interface you are still advertising it. With passive-interface prevents from forming neighborship only, but you still can advertise it.

interface Loopback0

ip address 172.16.255.4 255.255.255.255

!

router ospf 1

log-adjacency-changes

passive-interface FastEthernet0/0

passive-interface Loopback0

network 172.16.1.124 0.0.0.3 area 0

network 172.16.1.160 0.0.0.31 area 0

network 172.16.255.4 0.0.0.0 area 0

https://supportforums.cisco.com/docs/DOC-24683

Hope it will help.

Best regards,
Abzal

solemdoms5 · ‎12-24-2012

thank you for reply

Yes. I knew that. but If there is no hello packet. the neighboring relation is dead isnt it ?

I thought if the neighboring relation was dead , they do not advertise their route any more.

hence the routing table would be refresh . and the route would be delete

(In this case ,

on R5 ,O 172.16.255.4/32 [110/130] via 172.16.2.2, 00:19:58, FastEthernet0/0　●

would be deleted .)

Is this wrong ?

Abzal · ‎12-24-2012

Yes, you are right but it is not your situation. Here is you can simple check it by yourself, if make s1/0 passive interface, neighborship will be dead and all R4 advertising subnets will be deleted from routing table of neighbor (R5).

R4:

interface Serial1/0

ip address 172.16.1.126 255.255.255.252

encapsulation ppp

serial restart-delay 0

clock rate 128000

router ospf 1

passive-interface s1/0

Abzal

Best regards,
Abzal

solemdoms5 · ‎12-24-2012

I see

then Could you tell me

In this case ,How does passive-interface loopback0 work ?

Abzal · ‎12-24-2012

Refer these links, I hope it might help you to understand

https://supportforums.cisco.com/thread/202928

http://blog.ioshints.info/2009/07/when-passive-interface-command-is.html

Hope it will help.

Best regards,
Abzal

solemdoms5 · ‎12-25-2012

Abzal thank you for your reply .

I have read two links you give me .

one said that this is caused by IOS feature-set .and the problem has already resolved .

and another is the post 5 years old ago .

Do you think the problem in my situation is caused by IOS feature-set ?

On R4:

sh run | sec router ospf

On R5:

sh ip ospf network 172.16.255.4

also what do these command mean ?

could you give me command reference or explanation of this ?

Thank you .

Reza Sharifi · ‎12-24-2012

Hi,

Passive interface command doesn't prevent you from advertising the routes. It just will not send any packets (hello packet for example) using that interface.

HTH

solemdoms5 · ‎12-24-2012

HI

Passive interface command doesn't prevent you from advertising the routes. It just will not send any packets (hello packet for example) using that interface.

Yes. I knew that. but If there is no hello packet. the neighboring relation is dead isnt it ?

I thought if the neighboring relation was dead , they do not advertise their route any more.

hence the routing table would be refresh . and the route would be delete

(In this case ,

on R5 ,

O 172.16.255.4/32 [110/130] via 172.16.2.2, 00:19:58, FastEthernet0/0　●

would be deleted .)

Is this wrong ?

kalpeshnmodi · ‎12-25-2012

Hi Solemdoms,

What my understanding is - the network command works differently with Eigrp and Ospf than it works on BGP.

In BGP route is being advertised by network command.

But in Eigrp or OSPF when you apply network command, it enables the respective protocol on the interfaces which includes the covers the subnet on which it is applied.

Hence in this case you have applied the network command exactly on the loopback0 interface, it overrides the passive-interface loopback 0 command.

That could be the reason for this kind of output.

Let me know if any further confusion.

Kalpesh Modi

solemdoms5 · ‎12-25-2012

Hello kalpeshnmodi , thank you for your reply .

Hence in this case you have applied the network command exactly on the loopback0 interface, it overrides the passive-interface loopback 0 command.

I see , however Do you have any document verified ?

I have never heard that .

If you have it , Coud you give me the URL or the name of book .

Regards .