OSPF F/R 'ip ospf network broadcast'

Unanswered Question
Apr 18th, 2008


I have a hub & spoke design in my Lab.

2 spokes, 1 hub in a partial mesh config. I am using 'ip ospf net broadcast' on the serial sub-interfaces of each router. I have full connectivity.

I have frame-relay 'map' statements on each spoke pointing to the other spoke. I am not using the broadcast keyword on the map statements but still have full connectivity ???

Doyle I, is suggesting that I need this 'broadcast' keyword to forward multicast/broadcasts on this network type.

Although Doyle is using physical interfaces not sub-interfaces.

What am I missing here ?



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Overall Rating: 5 (2 ratings)
Richard Burts Fri, 04/18/2008 - 07:57


You mention having serial subinterfaces. Are these point to point serial subinterfaces? If so what you are missing is that ptp subinterfaces support broadcast/multicast by definition. You do not need the broadcast statement on the map because the broadcast/multicast is natively supported. In fact you usually do not have map statements with ptp serial subinterfaces, so the broadcast keyword is usually not an issue with ptp serial subinterfaces.



philth_123_2 Fri, 04/18/2008 - 08:17


I'm using multi-point sub-interfaces. I'm just gonna try a reboot incase something has been corrupted by previous configs.


philth_123_2 Fri, 04/18/2008 - 08:40

Reboot is the same ...

spoke 2

Interface Serial 0

no ip address

encapsulation frame-relay

no fair-queue

frame-relay lmi-type cisco


Interface Serial 0.100 multipoint

ip address

ip ospf network broadcast

ip ospf priority 0

frame-relay map ip 100

frame-relay interface-dlci 100


router ospf 1

network area 0



Interface Serial 0.101 multipoint

ip address

ip ospf network broadcast

frame-relay interface-dlci 101

frame-relay interface-dlci 201


Hmmmmm ? 'frame-relay interface-dlci ...'

Not sure how this could be affecting things


mohammedmahmoud Fri, 04/18/2008 - 10:03

Hi Phil,

It is "frame-relay interface-dlci", please check the output of "show frame map", and please check the following:


interface Serial0/0/0.2 multipoint

ip address

frame-relay interface-dlci 101

Rack6R6#sh fram map

Serial0/0/0.2 (up): ip dlci 101(0x65,0x1850), dynamic,


IETF, status defined, active

[edit] To explain what i wanted to say with the above output, if the command "frame-relay interface-dlci" is used under a multipoint subinterface, then the DLCI will be learned dynamically and supporting broadcast by default.


Mohammed Mahmoud.

lamav Fri, 04/18/2008 - 10:16


You don't need the broadcast keyword in the static mapping command because you have also configured the multipoint subinterfaces to use inverse ARP (dynamic mapping) to do the protocol address/DLCI mapping.

When frame-relay inverse-arp is enabled, broadcast IP traffic will go out over the connection by default.

If you remove the frame-relay interface-dlci command from the subinterfaces, you will then have to use the broadcast keyword for the static mapping.



lamav Fri, 04/18/2008 - 10:18


Sorry for the cross-post. Im glad you agree with me, though. :-)




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