configuring frame relay encapsulation

Answered Question
Aug 22nd, 2009
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Hi every body

I have few questions;


Let say we have three routers,r1,r2 and r3. All these routers are connected with with each other by frame relay . They are fully meshed as well.

Usually frame relay encapsulation is configured under physical interface. But i want to connect these routers using point-to multipoint int with frame relay encapsulation configured under it.

For example on r1

int s0

int s0/0.1 point-to-multipoint

encapsulation frame-relay


The other two routers are configured in the similar manner. Can i do this?



=========================


2) Same scenario but this time i want to configure encapsulation using frame-relay interface-dlci command, with this stipulation in mind that no frame relay encapsulation is configured either under the physical or sub interface on each router.

For example on r1

int s0

int s0/0.1 point-to-multipoint.

frame-relay interface-dlci 54 ietf

frame-relay interface-dlci 65 ietf

Where 54 is dlci for vc b/w r1 and r2

while 65 is dlci for vc b/w r1 and r3.


Can i do this?


Thanks a lot and have a nice weekend.

Correct Answer by Peter Paluch about 7 years 8 months ago

Hello Giuseppe,


Regarding the point-to-point subinterfaces and InverseARP: my experience is that a point-to-point subinterface does not send InverseARP requests by itself but accepts them upon receival and answers to them (it sends replies).


Best regards,

Peter


Correct Answer by Giuseppe Larosa about 7 years 8 months ago

Hello Lucien,

I agree this is necessary sorry I didn't write clearly in my post.


Best Regards

Giuseppe



Correct Answer by Lucien Avramov about 7 years 8 months ago

well well, you need still to have the frame-relay interface DLCI commands on the hubs and on the spoke, as detailed on my other post. That is the minimum FR config to get it to work.


Inverse-arp will take care of the ip addressing, but you need to say out of which DLCI it will go.



Correct Answer by Lucien Avramov about 7 years 8 months ago

You need at least the following command on the main side that is using the multipoint interface:

frame-relay interface-dlci DLCI_TO_R1

frame-relay interface-dlci DLCI_TO_R2


Also on the point to point subinterfaces, you need 1 only frame-relay command:

frame-relay interface-dlci DLCI_TO_R3



Then it will work, I just tested it.



Correct Answer by Giuseppe Larosa about 7 years 8 months ago

Hello Sarah,

I had some doubts on the capability of a point-to-point subinterface to advertise the DTE IP address over the DLCI.

For sure inverse-ARP is disabled on the receiving direction.

Then I checked on the CCIE exam certification guide third edition book and I've found an example like your scenario: a hub router with multipoint subinterface and two spoke routers.

The example shows with debug frame-rel events that the spoke with point-to-point subinterface advertises its network layer address on the DLCI.

if so no static mappings are needed.


This is handy for production networks with a lot of spoke routers.


Hope to help

Giuseppe

Correct Answer by Lucien Avramov about 7 years 8 months ago

2) You should have encapsulation frame-relay under the physical interface to be able to configure your s0/0.1 with point-to-multiploint

Correct Answer by Giuseppe Larosa about 7 years 8 months ago

Hello Sarah,


1)

no because enc frame-relay is not allowed in a subinterface you can specify the FR encapsulation per DLCI probably as an option in a frame-relay map command


yes frame-rel map supports the option for encapsulation

see


http://www.cisco.com/en/US/docs/ios/wan/command/reference/wan_f2.html#wp1012264


2)

yes

I never used frame-relay interface-dlci with multipoint subinterfaces but I think you can do it in this way or using frame-relay map command as I noted above.


command reference about frame-rel interface-dlci says:


>>This command is required for all point-to-point subinterfaces; it is also required for multipoint subinterfaces for which dynamic address resolution is enabled. It is not required for multipoint subinterfaces configured with static address mappings.


So yes to question 2


Notice that FR encapsulation must match on both DTE connected by the same PVC but it can be different on different PVCs on the same physical interface or multipoint subinterface.


Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Sat, 08/22/2009 - 13:40
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Hello Sarah,


1)

no because enc frame-relay is not allowed in a subinterface you can specify the FR encapsulation per DLCI probably as an option in a frame-relay map command


yes frame-rel map supports the option for encapsulation

see


http://www.cisco.com/en/US/docs/ios/wan/command/reference/wan_f2.html#wp1012264


2)

yes

I never used frame-relay interface-dlci with multipoint subinterfaces but I think you can do it in this way or using frame-relay map command as I noted above.


command reference about frame-rel interface-dlci says:


>>This command is required for all point-to-point subinterfaces; it is also required for multipoint subinterfaces for which dynamic address resolution is enabled. It is not required for multipoint subinterfaces configured with static address mappings.


So yes to question 2


Notice that FR encapsulation must match on both DTE connected by the same PVC but it can be different on different PVCs on the same physical interface or multipoint subinterface.


Hope to help

Giuseppe

Correct Answer
Lucien Avramov Sun, 08/23/2009 - 08:23
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2) You should have encapsulation frame-relay under the physical interface to be able to configure your s0/0.1 with point-to-multiploint

sarahr202 Mon, 08/24/2009 - 07:10
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Thanks Lucien and Guiseppe.


Let say three sides are conected in hub and spoke toplogy to main side. Main side is using sub interface multipoint type while each side is connected to main side by sub interface point to point type.

Will inverse arp take care of mapping ip-dlci at main side or i have to do manual mapping at the main side considering it is sub interface multipoint type at main side we are dealing with ?

thanks and have a nice weekend

Correct Answer
Giuseppe Larosa Mon, 08/24/2009 - 22:39
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Hello Sarah,

I had some doubts on the capability of a point-to-point subinterface to advertise the DTE IP address over the DLCI.

For sure inverse-ARP is disabled on the receiving direction.

Then I checked on the CCIE exam certification guide third edition book and I've found an example like your scenario: a hub router with multipoint subinterface and two spoke routers.

The example shows with debug frame-rel events that the spoke with point-to-point subinterface advertises its network layer address on the DLCI.

if so no static mappings are needed.


This is handy for production networks with a lot of spoke routers.


Hope to help

Giuseppe

Correct Answer
Lucien Avramov Mon, 08/24/2009 - 23:12
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well well, you need still to have the frame-relay interface DLCI commands on the hubs and on the spoke, as detailed on my other post. That is the minimum FR config to get it to work.


Inverse-arp will take care of the ip addressing, but you need to say out of which DLCI it will go.



Correct Answer
Peter Paluch Tue, 08/25/2009 - 01:52
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Hello Giuseppe,


Regarding the point-to-point subinterfaces and InverseARP: my experience is that a point-to-point subinterface does not send InverseARP requests by itself but accepts them upon receival and answers to them (it sends replies).


Best regards,

Peter


sarahr202 Tue, 08/25/2009 - 16:53
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Thanks Peter.


"my experience is that a point-to-point subinterface does not send InverseARP requests by itself but accepts them upon receival and answers to them (it sends replies)."



Is this default behavior or we have to configure:


no frame-relay inverse arp” ?



I was reading this side which implies inverse arp is not disabled on point to point interface.

Let me quote for easy reference.




"Frame-Relay Inverse ARP is not required on point-to-point interface, and, if needed it can be disabled with the following command under the interface you need to do it:


“no frame-relay inverse arp”


However, Inverse ARP Reply can NOT be disabled, that means, even if you disable your Inverse ARP in an interface, if this interface receives any Inverse ARP Request it'll respond to the request!"


Below is the link i quoted from:


http://cauew.blogspot.com/2008/05/frame-relay-inverse-arp.html


Thanks a lot Peter and hope you had good weekend.



Correct Answer
Lucien Avramov Mon, 08/24/2009 - 23:07
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You need at least the following command on the main side that is using the multipoint interface:

frame-relay interface-dlci DLCI_TO_R1

frame-relay interface-dlci DLCI_TO_R2


Also on the point to point subinterfaces, you need 1 only frame-relay command:

frame-relay interface-dlci DLCI_TO_R3



Then it will work, I just tested it.



Correct Answer
Giuseppe Larosa Tue, 08/25/2009 - 01:48
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Hello Lucien,

I agree this is necessary sorry I didn't write clearly in my post.


Best Regards

Giuseppe



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