[MLB-WIRELESS] RE: [RGSouthern] Just to prove we're not dead yet

[Dan Flett]

Ryan wrote:
 
> GHO, and the uplink nodes must be area 0.0.0.0.  Their interfaces
linking
> back to the cluster are on the appropriate region 0.0.0.9.

By this do you mean that all nodes that connect to GHO must specify
their GHO-linked interfaces as Area 0.0.0.0?  This means that any node
that connects to GHO is a backbone node.

> The uplink nodes will aggregate the routing tables for each region.

I've a question here: GHO's own address block (10.10.129.0/28) is
allocated from the OEF/Area 0.0.0.9 address space (10.10.128.0/20).
Won't aggregation of Area 0.0.0.9's routes fail because GHO's addresses
are smack bang in the middle of OEF's address space?  I thought OSPF
worked better with route aggregation if each area, including area
0.0.0.0, had addresses chosen from separate address spaces.  Shouldn't
GHO and any other Area 0 interface have addresses chosen from outside
existing Region Group address spaces?

When I get a chance I'll draw up some diagrams of what I'm talking
about.

Another issue with OSPF currently:  Johnno's nodes FOA, FOB and FOC are
in RGSouthern and are linked together.  In a separate cluster we have
Nodes GMR, GES, GEZ and AFH, also in RGSouthern.  In theory we're all
supposed to be Area 0.0.0.10.  We're currently linked via another area -
Area 0 (I assume Node ILE is Area 0).  Should we be virtual-linked?
OSPF wants areas to be contiguous.  If they aren't there needs to be
'virtual-link' or 'shortcut' (not sure which applies best here), and the
area that is doing the 'virtual-link' or 'shortcut' needs to be
specified in the config files of the concerned routers.

Also, what area is Node ILE in?  It has one link to OEF (Node GUR) and
two links to RGSouthern (Node FOB, Node AFH), and no direct links to
Area 0.0.0.0 (Node GHO).  However, if Johnno made FOB's interfaces to
GHO and ILE both Area 0.0.0.0 then at least the backbone would be
contiguous.

This link talks about shortcut ABRs
http://ietfreport.isoc.org/old-ids/draft-ietf-ospf-shortcut-abr-02.txt

This is why I don't like using OSPF with non-zero areas.  It's simply
too complicated for us non-network-engineer types.  OSPF expects areas
to be connected in a certain way.  Nodes in our network often don't link
up in a way that meets the expected topology - as shown in the examples
above.  We have to specify exceptions in our config files, and there's
no reliable way for information about config changes to get to other
node-owners.  LocFinder doesn't currently support the idea that a node
can be in more than one area at once, nor does it contain any
information as to a node's current OSPF configuration.  I suppose people
could try to keep their up-to-the-minute Quagga config files posted to
the Wiki, but how can we rely on this?  Again, it seems a bit too hard
to me.  And it's far too complex a system for a newbie to want to get
involved in.  A dynamic routing protocol should, at the very least, make
large-scale routing easier than using static routes.  Using OSPF the way
we use it seems to make it harder, not easier.

> I have spoken to several cisco nutbags at dimension data who say OSPF
is
> fine.  They have said that we could *possibly* use BGP for
inter-region
> links at a later stage if need be.
> 
> pffffffft.

Cool, well it's good we've got some nutbugs on side.  Can you tell us
what factors they base their decision on that OSPF is fine?  Do they
realise that 90% of the node-owners don't know much about routing, let
alone dynamic routing under Linux?  Do they realise that in our network
OSPF areas can and do become fractured as links appear and disappear?
Do they realise that there is no single administrative body that could
control of all routers on the network?

I've outlined my arguments against all-pervasive OSPF in this post and
in previous posts.  Do they have any counter-arguments?  I don't for one
second pretend that I have much experience at all to back up my
arguments.  I only know what I know from reading manuals, articles and
mailing lists.  The only practical experience I have is playing with
Quagga on the RGSouthern nodes.  But it seems that already, with the
recent re-linking of RGSouthern and RG-OEF, that OSPF is becoming
unwieldy.  I really would like to see some more informed debate on this
issue.

Cheers,

Dan

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