Frame-relay can't ping local interface

[bellocarico]

Hello, I've got a small problem with frame-relay lab.

This is made by 1 FR switch + 3 routers.

R1>

interface Serial0

bandwidth 64

no ip address

encapsulation frame-relay

!

interface Serial0.1 multipoint

ip address 10.10.1.9 255.255.255.248

no arp frame-relay

no frame-relay inverse-arp

frame-relay map ip 10.10.1.10 103

frame-relay map ip 10.10.1.11 102

R2>

interface Serial0

bandwidth 64

ip address 10.10.1.10 255.255.255.248

encapsulation frame-relay

no arp frame-relay

no frame-relay inverse-arp

frame-relay map ip 10.10.1.9 301 broadcast

frame-relay map ip 10.10.1.11 301 broadcast

R3>

interface Serial0/2

ip address 10.10.1.11 255.255.255.248

encapsulation frame-relay

no arp frame-relay

no frame-relay inverse-arp

frame-relay map ip 10.10.1.9 201 broadcast

frame-relay map ip 10.10.1.10 201 broadcast

!

As you can see R1 is a "central" router

and all the traffic between R2 and R3 supposed to pass

trought R1

Everything works fine, I can successfully ping from anywhere.

The ony thing that doens't work is the ping to

the from R1 to 10.10.1.9 (local Ip on the subinterface)

There are no access lists at all.

Is there anything I'm missing?

Thanks for your help!

[Richard Burts]

Stefano

Thanks for posting the config of the frame relay switch. But perhaps I was not clear in my request when I asked for the config of the central router, I meant to ask for the router that has two point to point subinterfaces and is getting every other ping successfully. Based on the symptoms I am guessing that the IP subnets of the two subinterfaces overlap and I would like to see the config of the two subinterfaces to verify this.

One question that does occur to me based on looking at the frame relay switch config is that it shows frame relay connections to two routers. But your problem involves three routers. Where and how is the third router connected?

HTH

Rick

[bellocarico]

Rick, you were right, I had the 2 interfaces on the "central router" with overlapping subnet.

So subinterface 0.1 multipoint and subinterface 0.2 point-to-point were both in the same subnet.

It was enough to move 0.2 to a different subnet to make everything magically work.

I actually cut manually the switch config myself as I was going over the maximum characters allowed per post.

Just to understand, why was 50% of the packets sent ok and 50% not? It sounds like a form of load balancing to me, but I'm still very confused on this.

My lab is actually made by a central router 2523 (FR switch) plus 4 routers. A "central" one with 2 subinterface 0.1 multipoint 0.2 point-to-point.

Of the other routers 2 are "connected" to the multipoint interface (0.1) where the last router is connected to subinterface (0.2)

Q4) As I said, now everything is working fine, I'm just trying to understand why was the network behaving like that (50% of packets loss)

Q5) Let's say I'm using the old config with subnet overlapping between subinterfaces, dowe have a way to "bridge" between the 2 rather than route?

Q6) Regarding adaptive-shaping, I've created my own class using map-class.

Now if I apply it to the central router (main interface), by default

the same class is used on the interface and both subinterfaces.

I've figured out that I need to create a second class and apply it to the second subinterface, but how to disable the class on the main interface without affect the subinterfaces?

Bottomline, I'd like to use a different class on a subinterface basis, but I'm not sure how the main interface coexists with the subinterfaces config.

Thanks to read!

[Richard Burts]

Stefano

Your comment that it sounds like a form of load balancing is pretty accurate. If the router has two interfaces in the same subnet it believes that it has two different paths to the same destinations. For packets generated by the router itself it will forward one packet over 0.1, the next over 0.2, the next over 0.1, the next over 0.2, and so on. So 50% of packets are sent over the interface that really connects to the destination and 50% are sent over the interface that does not connect to the destination. And this results in 50% packet loss.

I have a couple of comments about this:

- it is interesting that you can not configure two interfaces in the same subnet on LAN interfaces but can do this on serial interfaces. If you try a similar configuration on Ethernet/FastEthernet interfaces you would get an error message. But on the Frame Relay interfaces it is accepted.

- Logically a p-t-p interface (or subinterface) is an independent connection and needs its own unique subnet.

If you had the old config that had the overlapping address assignments I guess that you could configure Integrated Routing and Bridging, configure bridging on both frame relay intefaces, and configure a BVI with an address in that subnet. But that is way more complicated and I believe it would not be worth it to try to overcome a misunderstanding. It is better to just configure the two subinterfaces with separate subnets.

HTH

Rick

[Richard Burts]

Martin

The main reason I would not use Inverse ARP on a p-t-p frame relay subinterface is that I do not see that it adds anything of value. I did not remember that it ran on p-t-p subinterfaces but if you say you have run it then I guess that it does. But why do something that adds no value?

HTH

Rick

[mheusinger]

Hi Rick,

I checked my configs of those "old days" and found I didn´t use it! My memory is playing tricks on me. Sorry for causing confusion.

Martin

[Richard Burts]

Martin

It is no problem. There is so much to keep track of and trying to remember the many details is a challenge. I find that my memory of some of the details gets vague sometimes.

One of the good things about the forums is the opportunity to ask questions and to explore the reasoning of other people. The Cisco documentation is quite good about explaining what CAN be configured but sometimes a bit less helpful about what SHOULD be configured (should both commands be used or just one, and if just one which one is best for what situation). The forums are a good way to fill in some of that rationale.

I enjoy your participation in the forums and encourage you to continue.

HTH

Rick

[arvenugopal]

hi

its interesting that the comments and participation is encouraging. my 1 dollar comment i like to add. cisco documentation is no doubt a good resource.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fwan_c/wcffrely.htm

[bellocarico]

Q6) Regarding adaptive-shaping, I've created my own class using map-class.

Now if I apply it to the central router (main interface), by default

the same class is used on the interface and both subinterfaces.

I've figured out that I need to create a second class and apply it to the second subinterface, but how to disable the class on the main interface without affect the subinterfaces?

Bottomline, I'd like to use a different class on a subinterface basis, but I'm not sure how the main interface coexists with the subinterfaces config.

Thanks to read!

[bellocarico]

I've forgotten to ask:

Always talking about traffic shaping.

Once I've created the class,to apply this on the main interface I use the class command.

To apply the class to a subinterface point-to-point I use the frame-realy interf-dlci XXXX

and from here I use the class command to associate the it to this specific DLCI

But what about multipoint subinterfaces?

We said that we can't use "frame-relay interf-dlci" on multipoint, so how to apply a class ona DLCI basis here?

Thanks again, you're really helping out!!

[pkhatri]

Hi,

You can indeed use the "frame-relay interface-dlci" command on multipoint sub-interfaces. In fact, you would need to use this command when using multiple sub-interfaces on the same physical interface so that the router will know which DLCIs to associate with each interface. Therefore, when using multipoint interfaces, use the "frame-relay interface-dlci" command and then specify the map-class under it.

Here's an example of where you would use the "frame-relay interface-dlci" command on multipoint interfaces.

Consider the case where you have an interface Serial0 with 6 DLCIs on it - DLCIs 10, 20, 30, 40, 50 and 60. Your requirement is to have 2 multipoint interfaces with the first one containing DLCIs 10,20 and 30 and the second one containing DLCIs 40, 50 and 60. In this case, how would the router know which DLCIs belong to which multipoint interface ? You need to use the following config:

interface serial0

encapsulation frame-relay

!

interface serial0.1 multipoint

ip address x.x.x.x y.y.y.y

frame-relay interface-dlci 10

class class10

frame-relay interface-dlci 20

class class20

frame-relay interface-dlci 30

class class30

!

interface serial0.2 multipoint

ip address x.x.x.x y.y.y.y

frame-relay interface-dlci 40

class class40

frame-relay interface-dlci 50

class class50

frame-relay interface-dlci 60

class class60

!

Hope that helps... pls rate the post if it does.

Paresh.