Frame Relay

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May 6th, 2007
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I have hub and spoke topology. I tried to ping the local router interface then i am not able to ping but when i tried to ping the remote router interface then i am getting the reply from the remote router. so do i need to define the DLCI to the local interface also?


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mohammedmahmoud Sun, 05/06/2007 - 11:11
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Hi,


You must have been using a multipoint interface. You cannot ping your own IP address on a multipoint Frame Relay interface. To make a ping successful on a serial interface, an Internet Control Message Protocol (ICMP) echo request packet must be sent, and an ICMP echo reply packet must be received. Pings to your own interface address are successful on point-to-point subinterfaces or high-level data link control (HDLC) links because the router on the other side of the link returns the ICMP echo and echo reply packets.


The same principle also applies with multipoint (sub) interfaces. To successfully ping your own interface address, another router must send back the ICMP echo request and the echo reply packets. Because multipoint interfaces can have multiple destinations, the router must have Layer 2 (L2) to Layer 3 (L3) mapping for every destination. Because mapping is not configured for our own interface address, the router does not have any L2 to L3 mapping for its own address and does not know how to encapsulate the packet. That is, the router does not know which data-link connection identifier (DLCI) to use to send echo request packets to its own IP address resulting in encapsulation failure. To be able to ping its own interface address, a static mapping must be configured pointing towards another router over the Frame Relay link which can send back the ICMP echo request and reply packets.


http://www.cisco.com/warp/public/116/fr_faq.html



HTH, please rate if it does help,

Mohammed Mahmoud.

dangal.43 Sun, 05/06/2007 - 11:27
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so i am on the right track, it means my whole topology is up and running right!!!


one more question is for frame relay multipoint you need single DLCI to communicate with the all other peer router in multipoint is that right?

and i need to map my own interface ip address to that DLCI in order to get the ping back to my own interface is that the same thing you are talking about?



paolo bevilacqua Sun, 05/06/2007 - 11:55
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A very comprehensive answer by Mohammed, I would add one thing that he didn't mentioned:


The best setup for frame relay is using point-to-point sub-interfaces:


- Easier to implement and configure: no map statements that can go wrong, no need for a an address resolution protocol.


- Easier environment for routing protocols: no special case of NMBA, just basic point-to-point circuits.


- Easier management: The interface status will always reflect the PVC status, making easy to diagnose network faults.


- Easier secuirty management: Because each branch has his own dedicated interface, it's easier to apply QoS, ACL or any other configuration that ties to a whole interface.


There can be other reasons too, but the above alone has proved effective since almost 15 years now in most networks!


Please remember to rate all useful posts using the scrollbox below!

dangal.43 Sun, 05/06/2007 - 12:14
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so you mean to say i need to create point to point interface between hub and spoke.


means i have to creat the multiple point to point subinterfaces for each spokes.

mohammedmahmoud Sun, 05/06/2007 - 12:17
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Hi,


Yes this is the most optimum design.



HTH, please do rate all helpful posts,

Mohammed Mahmoud.

dangal.43 Sun, 05/06/2007 - 12:24
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mohammed what are the other points need to be consider during the design and configuration of frame relay network?

mohammedmahmoud Sun, 05/06/2007 - 13:12
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Hi,


Nothing special, its always according to your scenario, always try to use point-to-point subinterfaces rather than multipoint and consider using Frame Relay End-to-End Keepalives, you can find the most helpful documents here:


http://www.cisco.com/en/US/tech/tk713/tk237/tsd_technology_support_protocol_home.html



HTH, please do rate all helpful replies,

Mohammed Mahmoud.

mohammedmahmoud Sun, 05/06/2007 - 12:05
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Hi,


Using multipoint interfaces, each next-hop protocol address (peer) needs to be mapped to a single local DLCI on the router (L2 to L3 mapping).


Using point-to-point subinterfaces are much more recommended as nicely illustrated by Paolo.



HTH, please do rate all helpful replies,

Mohammed Mahmoud.

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