Subject: AW: AW: AW: AW: ifStackTable layering in L2TP

From: Klausberger Walter <[email-masked]>
Date: Wed, 13 Dec 2000 18:39:31 +0100

>-----Originalnachricht-----
>Von: Evan Caves
>An: Klausberger Walter
>Cc: ''Dave Thaler ' '; [email-masked] ' '; [email-masked] ' '
>Gesendet: 13.12.00 17:26
>Betreff: Re: AW: AW: AW: ifStackTable layering in L2TP

>> A LAC does not necessarily tunnel a PPP session (you might say it is
>> not a LAC then, but that's how it's written in the L2TP RFC). If a PPP
>> session is terminated in a LAC shouldn't the PPP layer be visible?

>I would think the PPP interface is visible in the ifStackTable and
>ifTable
>on the LAC until it gets tunneled. At the time a tunneling decision is 
>made it disappears (and should show up on the LNS). At this point you
>can use the l2tpSessionMapTable to see which interfaces (the interface
>that was below PPP before tunneling occurred) are having their packets
>switched to and from a particular tunnel/session.

That sounds reasonable to me. I see it the same way, but I wanted
confirmation on that.
 
>> Thinking about all this, I have concerns about the stack layering MIB.
>> When I have an AAL5 layer (assume PPP over AAL5), I know by
>> informations from the L2TP MIB that a PPP session is coming from the
>> AAL5 interface and going into a certain tunnel.
>> 
>> How do I know if IP packets come from that tunnel? To me there is
>> something missing, or does the CIDR MIB provide enough information
>> (I'm not so familiar with this MIB)?

>I am not sure what you mean. If you are asking whether PPP/IP packets
>are being tunneled the only way you can tell is by querying the
>LNS using the IPCP MIB. The CIDR MIB has nothing to do with this. It
>is used to manage the route table on a device.

Sorry, this was a mistype. I meant 'How do I know if IP packets come from
that AAL5 interface?'. I only see an interface.

- In case of PPP packets coming from this interface, I find an entry in the
L2TP MIB (in case of tunneling)

- In case of IP packets coming from this interface, do I get the information
via routing table (there should be a route to this IP interface)?

walter

---

From: Evan Caves <[email-masked]>
Date: Wed, 13 Dec 2000 15:48:59 -0800

walter wrote:

> Sorry, this was a mistype. I meant 'How do I know if IP packets come
> from that AAL5 interface?'. I only see an interface.
> 
> - In case of PPP packets coming from this interface, I find an entry
> in the L2TP MIB (in case of tunneling)
> 
> - In case of IP packets coming from this interface, do I get the
> information via routing table (there should be a route to this IP
> interface)?

The ipAddrTable (RFC 1213) will tell you what ifEntries have an IP
address configured on them.

evan
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