OSPF & Ring network

[Jeremy Evans]

Thanks for the suggestions. I'll bear them in mind for when I try tuning
the configuration.

Turned out I shot myself in the foot by rushing into upgrading BIRD to
the latest version after thinking I wasn't getting anywhere with 1.0.11
(I think - the version attached to ubuntu 8.04). I killed the daemon
instead of shutting down & it left the (non-optimal at the time) routes
in the kernel table. So, prior to starting up the updated BIRD, I
deleted all the 10.0.0.0/8 network routes manually.

Of course, this deleted the default ptp (neighbour) routes to the
adjacent PPP interfaces - which I was expecting BIRD to recreate
somehow.

In the end, my problem appears to be solved after restarting all the PPP
interfaces & letting the kernel populate the default ptp routes
automatically.

Now I just need to check the performance - what I'd like to be able to
do is in a (say) 5-node ring, normally node 1 will talk to node 3 via
node 2. If the link between 2 & 3 goes down, however, the traffic will
have to redirect through 5 & 4 instead.

Thanks for your help.

Jeremy Evans

-----Original Message-----
From: Ondrej Zajicek [mailto:santiago at crfreenet.org] 
Sent: Friday, 26 March 2010 12:53
To: Jeremy Evans
Cc: bird-users at trubka.network.cz
Subject: Re: OSPF & Ring network

On Fri, Mar 26, 2010 at 12:23:53AM +0100, Ondrej Zajicek wrote:
> 2) You probably don't want 'export all' to protocol ospf.
> That would lead to export routes from direct protocol to ospf
protocol,
> whis is not what you want (protocol ospf generates routes for
connected
> devices itself so these exported routes would be duplicates
> and would fill OSPF domain with unnecessary external LSAs).

I wrote that OSPF generates routes for connected devices itself,
but this is true for devices with standard (prefix-based)
IP addresses. Devices with peer addresses does not generate
OSPF routes itself (they are considered as unnumbered ptp
links). But this is not problem (if you don't care that you
wouldn't have routes to these IP addresses in routing tables)
because such IP addresses should not be used anywhere else
than as destination in routes.

You would probably want some IP address that is used as 'canonical'
address of that computers. You don't want to use IP address
of some PPP iface for that purpose, as PPP ifaces might appear
and disappear and most importantly, neighbors would always
consider such address accessible through direct PPP link,
regardless of what OSPF says (and what is a state of a link).

This is usually handled by adding 'dummy' interface with
canonical address (with /32 prefix) and adding this interface
to OSPF (perhaps as stub interface). Often for the same
purpose is used IP address of some ethernet interface with
no other OSPF neighbors.

Another way of exporting canonical address is to specify it
using 'stubnet' declaration in OSPF area specification.
This can be also used to export IP addresses of ppp links,
if you really want them in routing tables.

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."