PPPoE over L2TP over GigE questions
Robert E. Seastrom
rs at seastrom.com
Tue Jun 17 07:17:12 CDT 2008
That's some really good news... does it mean they're getting rid of
the ATM network and the *&()&* Newbridges too?
It's been a year and a half since I've even logged into the LNSes in
question, and over two years since doing any meaningful
reconfiguration... but it's good to hear my friends in Canada are
getting improved service from Bell in some areas, even if they offset
it by doing stupid stuff in other areas. :-/
Francois Menard <francois at menards.ca> writes:
> Actually, with AGAS, there are no tunnel switches anymore
> multiple tunnels are set-up directly netween Juniper ERXes aggregating
> DSLAMs and acting as LAC's and the ISPs LNS's receiving the L2TP
> This is one giant step towards TR-101, but Bell won't accept to do this
> On 11-Jun-08, at 3:37 PM, Robert E. Seastrom wrote:
>> Jean-François Mezei <jfmezei at vaxination.ca> writes:
>>> Pardon my ignorance on the subject, but I would need to know how
>>> between a BAS/LAC and an ISP's router are transported (this is within
>>> Bell Canada ADSL territory).
>>> Bell uses L2TP to link each BAS/LAC to the ISP. Some of the ISPs
>>> get a
>>> Gigabit Ethernet link to the Bell cloud.
>> Actually, they don't set up connections directly from the BASes and
>> SMSes anymore. I'm quite sure they've got some old Redback kit still
>> out there too, as well as perhaps some other ancient stuff.
>> You're going to be talking to a tunnel switch (TSW2-TORONTO63 for
>> instance). These are all Juniper ERXes to the best of my knowledge.
>> N number of BAS/SMS devices talk to a TSW, which talks to your LNS.
>> This cuts down drastically on the number of tunnels that you have to
>> manage (Bell has a couple of hundred BASes out there last I checked).
>> Brings the number of tunnels (and VLANs) down to a couple of hundred.
>> The tunnel switch is smart enough to look inside the authentication
>> packets at session start time and switch you properly based on the
>> realm the customer is logging into.
>>> Would the L2TP payload be an ethernet packet which contains a PPPoE
>>> packet, or would the L2TP payload be the PPPoE packet only ?
>> My recollection is that it includes the src/dst MAC addresses and the
>> rest of the ethernet header in the L2TP frame.
>>> Also, while I am at it:
>>> Architecturally, is a BAS considered a router, or a bridge/switch ?
>>> (since the PPPoE packet has no routing information (source,
>>> destination), it is the BAS which maintains the table of
>>> source/destination for each PPPoE session ID. Yet, the BAS machines
>>> supposedly Juniper ERX routers in Bell territory...
>> I'd call them VPN endpoints for a layer 2 VPN; thus the functionality
>> they're providing is more like a bridge than a router, notwithstanding
>> their peeking into layer 5.
>>> And while I am at it:
>>>> From the end user point of view, the ADSL modem sends all ATM
>>>> frames to
>>> a predetermined ATM destination (VPI/VCI). I assume that VPI/VCI
>>> to the BAS.
>> Yes, and at that point it's PPPoEoATM. Which gets turned into
>> PPPoEoATMoL2TP on the upstream side of the BAS.
>>> How does the BAS address ATM packets back to an individual
>>> subscriber ?
>>> Do each subscribers get their own VPI/VCI that points to the right
>>> on the right DSLAM ?
>> Nothing that's visible on the upstream side of the BAS - it's all
>> src/dst mac address at that point.
>>> And in cases where the telcos are extending the ethernet to the
>>> with the fragmentation into multiple ATM frames limited to the ADSL
>>> itself, how does the BAS address invididual customers ? Does each
>>> port on the DSLAM get its own ethernet address ?
>> the ADSL router has its own ethernet address.
>>> (since some services do not use PPPoE, I have to assume that the
>>> doesn't base its packet switching on PPPoE session IDs.)
>> These other services are VLAN-per-customer and don't use PPPoE or L2TP
>> at all. I think we looked at these and decided not to use 'em.
>> You may be thinking too deeply about this though. Contact me offline
>> if you want a working redacted config for Cisco kit talking to Bell
>> Canada. :-)
> François D. Ménard
> francois at menards.ca
More information about the NANOG