OSPF on SHDSL problem

Answered Question
May 14th, 2008
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Hello Guys


I have very strange problem to setup very simple OSPF between 3 routers in hub-spoke scenario.

Here is config from hub router in main office:


interface ATM0/1/0

no ip address

ip directed-broadcast

ip pim sparse-mode

no atm ilmi-keepalive

!

interface ATM0/1/0.1 point-to-point

ip address x.x.x.x 255.255.255.252

ip ospf network broadcast

ip ospf priority 50

pvc 0/35

encapsulation aal5snap

!

!

interface ATM0/1/0.2 point-to-point

ip address x.x.x.y 255.255.255.252

ip directed-broadcast

ip ospf network broadcast

ip ospf priority 50

pvc 0/36

encapsulation aal5snap



router ospf 10

log-adjacency-changes

network x.x.x.x 0.0.0.7 area 0

network 192.168.x.0 0.0.0.255 area 0


On the one of remote routers config is following:


interface ATM0/0/0

ip address x.x.x.x 255.255.255.252

ip directed-broadcast

ip ospf network broadcast

atm ilmi-keepalive 3

pvc 0/35

encapsulation aal5snap

!

!

router ospf 10

log-adjacency-changes

network x.x.x.x 0.0.0.3 area 0

network 192.168.y.0 0.0.0.255 area 0



Here is problem:


OSPF communication is established for the first time and after dead timer expire (in 40 sec) connection is broken and is reestablished after 10 sec. So it produce route flapping.


It is appear only on HO router and it constantly flap routes. For the remote site router everything appear OK.


I ran debug ip ospf events and got that HO router is sending hello packets but not receiving any ospf hello packet.


On the remote router hello packets are sent and received and there is no problem with routes.


Dule

Correct Answer by paolo bevilacqua about 9 years 1 month ago

Why you set ip ospf network broadcas on a p-t-p link?

and why "ip direct-boradcast" ??

These commands are not necessary.


What is necessary is that the remote router you configure a p-t-p subif also.

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t814687 Fri, 05/16/2008 - 12:33
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Dule,

Have you checked basic IP connectivity between the hub and spokes, you can ping back and forth and there is no packet loss?

Make sure MTU size on the interfaces is the same.


-serg

Correct Answer
paolo bevilacqua Fri, 05/16/2008 - 12:52
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Why you set ip ospf network broadcas on a p-t-p link?

and why "ip direct-boradcast" ??

These commands are not necessary.


What is necessary is that the remote router you configure a p-t-p subif also.

dusanamrtic Fri, 05/16/2008 - 15:56
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Thank you for your response. Unfortunately to do this I had to go to remote site otherwise connection will be broken.


Anyway I solved problem by introducing Tunnel interfaces and it work fine now.


Regards

paolo bevilacqua Sat, 05/17/2008 - 02:23
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When you need to configure remotely and connection can be broken, prepare the configuration on a file and copy to startup-configuration (nvram). Then reboot.


With tunnels you'll have more overhead and less MTU for an application that should work fine natively.

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