L2TP Traffic PPP Question

Answered Question
Oct 22nd, 2009

I hope I'm in the right forum.

Please let me know!

When a providers LAC which could be many try to establish an L2TP Tunnel connection (1 LAC IP Loopback address pointing to 4 IP Loopback address on 1 LNS) and the tunnels come up and start passing ppp traffic, we notice that the ppp signals contained within the tunnels are unbalanced. Obviously, the tunnels don't come up all at once so it's normal that the ppp traffic being passed would be unbalanced.

My question is "Does this create a problem on the customer end?"

If the Tunnels don't come up at the same time causing the passing of unbalanced ppp traffic, does this or would this create unpleasant internet connections for our customers in respect to if the tunnels did come up at the same time and the sessions were balanced properly?

I have this problem too.
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Correct Answer by Giuseppe Larosa about 7 years 3 months ago

Hello Paolo,

>> Having 4 flows = L2TP tunnels of different traffic volume can have an impact if there are parallel paths where load balancing can occur."

just to say that only possible issue I see is that of possible saturation of a routed link in the path if multiple paths are available to CEF in intermediate devices and one is more used then others (because it is used to forward traffic for the most loaded L2TP sessions)

Hope to help

Giuseppe

>> P.S. Sei Italiano? Io lavoro a Milano..

Sì sto a torino

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Giuseppe Larosa Thu, 10/22/2009 - 03:43

Hello Paolo,

it shouldn't be an issue PPP packets of a specific PPP session extended over L2TPv2 should be on the same tunnel.

A session-id is allocated for each transported PPP session.

see

>> A Tunnel ID is used to multiplex and demultiplex tunnels between the LAC and LNS. A session ID is used to identify a particular session with the tunnel.

http://www.cisco.com/en/US/tech/tk801/tk703/technologies_tech_note09186a0080094586.shtml#tunnelingprotocols

traffic of all L2TP parallel tunnels will go over the same physical paths (if destination addresses are published in the same way over the routing protocol).

Having 4 flows = L2TP tunnels of different traffic volume can have an impact if there are parallel paths where load balancing can occur.

But it shouldn't be a problem having more PPP sessions carried over one L2TP tunnel.

Hope to help

Giuseppe

Mavrick25 Fri, 10/23/2009 - 00:16

Giuseppe,

You always seem to be of great help.

But I didn't quite understand this phrase:

"Having 4 flows = L2TP tunnels of different traffic volume can have an impact if there are parallel paths where load balancing can occur."

You have been a great help!..

Mav

P.S. Sei Italiano? Io lavoro a Milano..

Correct Answer
Giuseppe Larosa Fri, 10/23/2009 - 00:40

Hello Paolo,

>> Having 4 flows = L2TP tunnels of different traffic volume can have an impact if there are parallel paths where load balancing can occur."

just to say that only possible issue I see is that of possible saturation of a routed link in the path if multiple paths are available to CEF in intermediate devices and one is more used then others (because it is used to forward traffic for the most loaded L2TP sessions)

Hope to help

Giuseppe

>> P.S. Sei Italiano? Io lavoro a Milano..

Sì sto a torino

Mavrick25 Fri, 10/23/2009 - 02:08

Giuseppe,

Grazie Mille!!

I think we are on the same page.

The problem is that our NOC divison for some reason, all the time they notice that the L2TP tunnels are unbalanced they ask us to clear the tunnels.

I don't understand why, I agree with you 100% and want to say thank you for everything..

Sei hai linkedin aggiungimi..

Ho notato che se sei sempre tu che mi aiuti su questo forum.. Grazie mille..

Sono Canadese e' lavoro a Milano spero che capisci il mio Italio..

Se hai linkedin aggiungimi,

Grazie

Paolo Jino Raimondi

[email protected]

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