Stewart,
You are stating the most obvious:)
For a feature to work, e.g. encapsulating into an RSVP tunnel, the entry
point of the packet must be able to support that feature. That is not a
problem. That how the entire world works:)
SR-based ti-uloop avoidance is no different. So if a packet arrives at
node "D" for example, then node "D" must be able to steer the packet
such that it guarantees loop-freeness.
Once "D" source-routes the packet into the loop-free path towards the
destination "Z" , downstream routers from "D" towards "Z" need NOT have
the ability to do uloop avoidance or even know that packets was
source-routed by node "D"
As for the need for using "strict" vs "loose" source routing, that is
topology dependent. The same applies for ti-lfa, rLFA, or even directly
connected LFA.
One last thing, if you think that source routing can reduced to a
"tunnel" we might as well shutdown SPRING WG:)
Ahmed
On 7/19/2016 7:48 AM, Stewart Bryant wrote:
Appologies if this is a duplicate.
The RFC that had all of the generic methods that were known at the
time of publication is RFC5715.
The two phase methods were in section 6.2 (near-side) and section 6.3
(far-side). The first describing tunnelling the traffic towards the
repair (and continue to use the repair), the second describing
tunnelling traffic towards the destination. For the purposes of this
discussion source routing of all flavours can be considered a type of
tunnel.
If this approach is a new genetric two phase method, it would be
useful to articulate it in general terms.
The type of topology that I was trying to explain in the meeting is as
follows
A-B-C-D-E-F-H-I-J.....W
| |
| |
+------X-Y-Z----------+
All costs are 1 and Y has failed.
Traffic to Z can enter enywhere, and is protected by X.
When the network starts to converge ALL the routers A..J will need to
update their fib to forward towards Z via W rather than towards X via A.
If they do this in a random order as would be the case without LF
convergence then you may precipitate microlooping.
What you need to do is to force the packets toward either X or Z using
a tunnel, or a source routed path, and as far as I can see you need to
do that at every point of potential entry into the network, in the
above case A..J, else you risk a microloop.
Now I suppose that if ALL packets were source routed, then you could
consider that the network was constantly in the first phase, but I
think that you would need to use strict source routing, rather than
loose source routing else it reduces the the problem I describe above.
- Stewart
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