[LibreQoS] routing protocols and daemons

[dan]

Keep in mind that often (wisps:  mikrotik, ubiquiti) run gear that often
have mediocre implementations of OSPF (and other protocols) and the
products are made to be as cheap as possible so hardware issues are more
likely than an enterprise vendor.

I field a lot of OSPF questions in support forums and they usually come
down to automatic IDs being set incorrectly because admin didn't set
them.... or the big ticket item being MTU.   MTU on the router's interface,
MTU issues on the radio links, or radios that say one MTU and aren't
passing it for some reason.  Also attempts to use broadcast and that being
unreliable over wireless networks.  Those things kinda make OSPF 'finicky'.

I would very much prefer ISIS for a number of reasons, mainly around
simplicity and reduction of finicky issues and dedicated PTP subnets and
configs etc.  ISIS is not available on mikrotik or ubiquiti products so
there you go.

Ultimately though, these are just shortest hop path builders and need some
other kit on top of them to do any sort of traffic engineering or load
balancing.  ECMP doesn't work for me, and doesn't work for a lot of wisps
so much so that after they've spent the time and effort to implement, they
undo it because different link characteristics make ECMP wreck their
customer's experience.  The 'E' for equal also is a PITA, requiring you to
start stacking up VLANs for example to get a ratio of 'ECMP' across
disimmilar links.

On Sat, Oct 29, 2022 at 7:48 AM Herbert Wolverson via LibreQoS <
libreqos at lists.bufferbloat.net> wrote:

> Juliusz, it's a pleasure to meet you. I've seen your name quite
> often in the async/await world. Admittedly, usually in the detailed
> "how things work" part - while I tend to be on the "teaching how to
> use an implementation" side of things.
>
> > > Dijkstra's algorithm remains a very natural approach to mapping a
> > > graph
> > I'm not sure what that means.  Dijkstra's is a shortest path algorithm,
> > it's not in the business of mapping.  I guess the author meant that
> > representing a graph as an adjacency list (the LSDB) is natural, which is
> > certainly true, but in no way specific to OSPF.
>
> Absolutely. Most of my development background is in game development,
> I also do a lot of GIS. In both fields, Dijkstra's algorithm - and its
> adaptations
> (A*, weighted flow maps, etc.) refer to mapping in the spatial sense; and
> converting
> a map to a node graph (whether grid, waypoint, etc.) and then working with
> cost-based adjacency (not raw adjacency) is a very natural way to
> resolve the issue of "how do I get from X to Y" on a map. It's in no way
> specific to OSPF (although specific adjacency cost specification was
> one of many reasons OSPF outperforms RIP).
>
> OSPF is where it is now because it's "good enough (for now)" and just
> about everything supports it. Sure, an implementation that spits out bad
> LSAs is going to break everything - you're going to get some pretty nasty
> results from sending out broken destination-distance-vector data, too.
> Garbage-in, garbage-out is one of the few truly universal rules! I agree,
> though - I wouldn't hand out large-scale OSPF administration to the new
> guy (although "here's the standard router config, plug in the numbers for
> the locally attached networks here" does work).
>
> I'd love to see good support for dynamic capacity analysis, unequal
> cost multipath and similar. Babel looks very promising, but the chicken-egg
> problem is very real; I can't put it to use until it's widely available,
> but
> it won't become widely available until enough people put it to use. (It
> seems like wireless vendors are busy trying to reinvent it at layer 2 with
> proprietary meshing that doesn't talk to other proprietary meshing; ugh)
>
>
>
>
> On Sat, Oct 29, 2022 at 4:15 AM Juliusz Chroboczek <jch at irif.fr> wrote:
>
>> > our toasts to the builders of Notre-Dame.
>>
>> ...which then burnt down :-/
>>
>> > Dijkstra's algorithm remains a very natural approach to mapping a
>> > graph
>>
>> I'm not sure what that means.  Dijkstra's is a shortest path algorithm,
>> it's not in the business of mapping.  I guess the author meant that
>> representing a graph as an adjacency list (the LSDB) is natural, which is
>> certainly true, but in no way specific to OSPF.
>>
>> > I don't suppose you have ever had any ideas to how to improve things?
>>
>> Modern OSPF and IS-IS have pretty much reached a local optimum: all the
>> low-hanging fruit has been picked, I doubt there's much that can still be
>> done to improve them without a complete redesign.  Well-implemented OSPF
>> and IS-IS work beautifully in a well-administered network, any other
>> protocol is going to converge slower and give less visibility into the
>> network.
>>
>> On the other hand, OSPF is extremely fragile in the presence of bad
>> implementation.  If two routers have the same id, OSPF is going to create
>> routing pathologies.  If a router corrupts its LSDB (for example due to
>> bad RAM), OSPF will create routing pathologies which will only go away
>> once the faulty LSA expires (30 minutes worst case).  If a router runs out
>> of memory for its LSDB, it needs to stop participating in the protocol,
>> lest it cause routing pathologies (IS-IS has the overload bit to deal with
>> this case, which causes the router to become a stub router).  Compare this
>> with distance vector, where a corrupt routing table entry will only
>> interfere with the traffic to that particular destination, and where it is
>> perfectly correct to run with a partial routing table.
>>
>> OSPF also requires a skilled administrator.  Splitting a network into
>> areas without causing suboptimal routing takes significant skill, route
>> filtering can only happen on area boundaries, and there are multiple
>> different ways of redistributing routes into OSPF (external LSAs).
>>
>> In my opinion, you want to be running OSPF in parts of your network that
>> are implemented with reliable gear and are managed by a competent
>> administrator, but you'll prefer a modern distance-vector protocol
>> (somebody mentioned Babel) where the hardware is cheap and the
>> administator is busy with other things.  Fortunately, due to the
>> flexibility of route redistribution in distance-vector protocols, you can
>> do both: a stable backbone using OSPF, and unadministered Babel bits at
>> the edges.
>>
>> -- Juliusz
>>
> _______________________________________________
> LibreQoS mailing list
> LibreQoS at lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/libreqos
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.bufferbloat.net/pipermail/libreqos/attachments/20221029/bf2b965d/attachment-0001.html>