Hello Robert,
Tony brought up the example of a partioned network.
But there are more examples.
E.g. in a network there is a router with a 1000 neighbors.
(When discussing distributed vs centralized flooding-topology
reduction algorithms, I've been told these network designs exist).
When such a router reboots/crashes/comes back up, all 1000 neighbors
will create a new version of their own LSP. This causes a 1000 different
LSPs to be flooded through the network at the same time. Impacting every
router in the network.
The case I was thinking of myself, was when a router in a large network
boots. When it brings up a number of adjacencies, each neighbor will
try to synchronize its LSPDB with the newly booted router. As the newly
booted router will send emtpy CSNPs to each of its neighbors, each
neighbor will start sending the full LSPDB. If such a network has 10k
LSPs, and such a router has 100 neighbors, that router will receive 100
* 10k
is 1 million LSPs. Having a faster and more efficient flooding
transport,
with flow-control, will make a reboot in such a topology less painful.
(In that last case, creative use of the overload-bit could prevent
black-holing
or microloops while ISIS synchronizes its LSPDB after a reboot. Just
like we
used the overload-bit to solve the problem of slow convergence of BGP
after
a reboot, 22 years ago. I have no idea if there are any implementations
that
use the overload-bit to alleviate slow convergence of IS-IS after a
reboot).
henk.
Robert Raszuk schreef op 2019-07-24 15:33:
Hey Henk & all,
If acks for 1000 LSPs take 16 PSNPs (max 66 per PSNP) or even as long
as Tony mentioned the full flooding as Tony said may take 33 sec - is
this really a problem ?
Remember we are not talking about protocol convergence after link flap
or node going down. We are talking about serious network partitioning
which itself may have lasted for minutes, hours or days. While just
considering absolute numbers yelds desire to go faster and faster, if
we put things in the overall perspective is there really a problem to
be solved in the first place ?
Would there still be a problem if LSR WG recommends faster acking
maybe not for each LSP but for say 20 or 30 max ?
Thx,
R.
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