There is plenty of L2TP still in use.
Yours,
Joel
On 6/9/2021 6:23 AM, Stewart Bryant wrote:
Sequence number checking in the forwarder is always a problem because it
is stateful so I doubt that many high-scale or high-speed forwarders
ever did this.
I think there is an undisclosed assumption that go up enough levels and
its IP so sequence number checking in the transport network (as opposed
to the transport layer) is not really needed.
I doubt that there is much L2TP still out there. It was in its prime
with dialup modems. L2TPv3 which was intended to replace it became niche
with, as Andy says, operators who did not want MPLS. Much of what L2TPv3
was intended for was actually done with PW over MPLS with some
replacement with by Mac in Mac for cost reasons.
If Carlos does not know the answer, Mark T would be my next port of call.
Stewart
On 8 Jun 2021, at 22:41, Andrew G. Malis <[email protected]
<mailto:[email protected]>> wrote:
Bob,
In addition to the cases listed by Derek, L2TPv3 can also carry non-IP
pseudowire data, such as Ethernet frames (see RFC 4719 for example).
Even though 4719 says that sequencing is optional, I would certainly
recommend it :-).
But I guess that's really not what you were asking about, since you
specifically mentioned IP data. But it is a case where you would
probably see sequencing in use.
Back in the day, Sprint made good use of Ethernet over L2TPv3, as they
were in the anti-MPLS camp at the time. But that's water over the
bridge, and I really don't know if this solution continues to be in
active use. Mark Townsley might know.
Cheers,
Andy
On Sat, Jun 5, 2021 at 10:07 AM Derek Fawcus
<[email protected]
<mailto:dfawcus%[email protected]>> wrote:
On Fri, Jun 04, 2021 at 03:13:15PM +0100, Bob Briscoe wrote:
> The L2TP RFC says sequencing /can/ be disabled for IP data, but it
> doesn't say SHOULD or MUST. Is it possible that some operators
enable
> L2TP sequencing for IP data? And if so, do you know why they would?
> Also, are you aware of any other types of tunnel that might try
to keep
> IP data packets in sequence?
How many intermediate headers are you considering between L2TP and
where
a carried IP header may exist?
Maybe I'm getting the wrong end of the stick, but surely this engages
the text from section 5.4 of RFC 2661:
"For example, if the PPP session being tunneled is not
utilizing any stateful compression or encryption protocols and is
only carrying IP (as determined by the PPP NCPs that are
established), then the LNS might decide to disable sequencing as IP
is tolerant to datagram loss and reordering."
This would then suggest if L2TP is carrying PPP, the PPP session
is not
multi-link, and is making use of compression (including one of the
versions of IP header compression) in some form for IP packets, then
reordering will impact the ability to decompress.
So such an L2TP data session may well make use of sequence numbers to
prevent reordering.
I guess similarly in L2TPv3 when the PW is for PPP, and possibly also
the fragmentation scheme in RFC 4623 which requires sequence numbers;
and such PWE3 links could ultimately be carrying IP packets.
DF
(not an operator)
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