ATM encapsulation : aal5ciscoppp or (aal5snap+protocol ppp)?

[Kevin Dorrell]

I have just been playing with ATM in the (remote) lab for first time, and I was looking at lab 3 in the CiscoPress "CCIE Practice Labs" book. The problem they set is to make a ATM link with PPP so that you can apply CHAP authentication over the top of it.

The solution they propose in the book looks something like this:

<b>

interface ATM0/0:101 point-to-point

 pvc 0/101

  protocol ip 10.99.99.1 broadcast

  encapsulation aal5ciscoppp Virtual-Template1

!

interface Virtual-Template1

 ip address 10.99.99.2 255.255.255.0

 ppp authentication chap

</b>

Now, for some strange reason, the router I was working on did not support the aal5ciscoppp keyword. So instead I used

<b>

interface ATM0/0:101 point-to-point

 pvc 0/101

  encapsulation aal5snap

  protocol ip 10.99.99.1 broadcast

  protocol ppp Virtual-Template1

!

</b>etc.

That seemed to work OK. Not sure about the protocol ip line though - I'll have to go back and check it out.

Can anyone tell me anythiong about the difference between the two configurations? Is one Cisco proprietary and one standards-based PPPoATM? If so, why do they both exist, and why was the aal5ciscoppp keyword not supported in 12.2(15)T9? Has one been obsoleted or something?

I had another small problem: I tried to add protocol cdp broadcast. Mindful of the fact that Frame Relay disabled CDP by default, I also set cdp enable on the main interface. But I still did not see the other router through CDP. (Note: ping worked OK.) I shall try it again next time I have a lab slot, but can anyone think of anything obvious I might have missed?

Thanks in advance for your responses.

Kevin Dorrell

Luxembourg

[m.lammerse]

Hi Kevin,

regarding your second question. CDP is only supported on SNAP-encapsulated links.

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a008030c764.html#1000952

The ppp encapsulation (Cisco or non-Cisco) , doesn't support SNAP.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/wan_r/wan_d1g.htm#wp1033188

I'm still trying to figure out your first question..

HTH,

Marcel

[Kevin Dorrell]

Marcel,

Thanks for the reply. As I said, this is my first sortie into ATM, so I am still getting confused by all those different encapsulation options, and their capabilities. I'll get there in the end, and the links you posted were very helpful.

The second one seems to say that CDP is not supported at all on ATM interfaces regardless of the encapsulation. But that cannnot be right, otherwise they would not have bothered with the protocol cdp command at all. I'll check it out better when I have accumulated enough questions to justify buying another remote lab session.

The next thing to investigate will be ATM QoS of course, and that should open a whole new can of worms.

Thanks again.

Kevin Dorrell

Luxembourg

[Kevin Dorrell]

Bump. Can anyone help me out on the first question?

Kevin Dorrell

Luxembourg