frame relay interface

[morialpesh008]

Hi,

     I have create frame relay topology, as per my knolwldge frame relay has default physical interface mode is Non-broadcast so  no broadcast will be forwarded on that interface,  when create ospf route on router frame relay physical  interface we must configure neighbour manually because of Non-broadcast mode and then neighbour relationship will for made,

But when configure eigrp on same router then no need to define neighbor , neighbor relationship adjacent automatically, then why under eigrp domain no need to define neighbor even interface in non-broadcast mode ,

Thanks.

[Georg Pauwen]

Hello,

what exactly do you mean by defining EIGRP neighbors ? As long as there is IP reachability between two routers, whatever interface you define as being EIGRP-enabled (with the network command) will form and adjacency.

[morialpesh008]

Hi

  What I mean in which circumstenses we must define neighbor manually under ospf and eigrp domain when using frame relay.

Thanks.

[paul driver]

Hello

Any non broadcast media type such as frame relay, but you can set this be broadcast capable within the frame relay

Broadcast capable-- Ethernet

res

paul

[morialpesh008]

Hi,

   kindly see attached snap of GNS3 scenario, i have created frame relay topology, and then configure EIGRP on all router.

by default frame relay network is NBMA network so it will not allow any broadcast or multicast on any frame relay interface.

but when i enable Debug ip packet then frame relay interface will sent received broadcast and multicast and EIGRP neighbour relationship established automatically why this happening?

 

[paul driver]

Hello

As I have stated frame relay will dynamically assign a LMI mapping as broadcast,
sh frame-relay map

With Eigrp enabled on these interfaces, By default it will see this as broadcast link type so will Multicast for its peering (224.0.0.10)

Ospf by default sets NBMA interfaces to NON Broadcast ( eigrp doesn't have this facility) and as such you need to specify the neighbor command in ospf to establish peering ( unless you change its ospf link type manually)

Now If you statically configure a FR mapping and disable inverse-arp on the serial interfaces then the eigrp peering wont establish without you specifying the neighbor command as it now see the lmi mapping a static.


res
Paul

[morialpesh008]

Thanks paul for clarification.

[paul driver]

Hello
It all depends on the encapsulation of the serial interface.

Serial interfaces default to HDLC encapsulation with is my understanding is basically a point-to-point protocol, and as such you wouldn't require specifying any unicast neighbor command either in ospf or eigrp and the peerings would establish.

However a frame-relay encapsulated serial interface is different - By default on a main serial interface this is by default a multipoint interface so to obtain connectivity you would require a FR switch to map the local dlci mappings between each router either by dynamic inverse arp or static mapping

Or, if you have back-back ( dce/dte) connections( no FR switch) you could negate the lmi keepalives, and statically configure the interfaces with the same local dlci mapping on each router and connection would be obtainable , not forgetting provide the clocking on the DCE router also, But with this conection you would require to specify eigrp neighbor command to obtain peering.

As eigrp neighbors can only form in either multicast or unicast, When you specify neigbour command you are saying to allow unicast hellos to form the adjacency but this will not stop the multicast hellos being sent, to do that you need to make the interface passive.

I think what you are seeing is maybe with your dynamic or static frame-relay mappings and with end to end connectivity do see Eigrp multicast hellos being seen and and as such adjacency is established.

Without knowing you current FR setup at this time its more guess work than fact.

Can you share:
sh int serial x/x
sh frame-relay map
sh frame-relay lmi



res
Paul