[Xorp-users] Problems with Linux kernel and OSPF ???
Aidan Walton
awalton at wires3.net
Wed Dec 5 10:54:04 PST 2007
Hi Atanu,
Now that I'm over the panic of collecting the data and recovering the
network. I can see that the neighbour seems to have been up for 29hrs
but adjacent for only 8mins. Clearly the adjacency has been dropped and
even though it has recovered it no longer imports the routes from the
database. Unfortunately because I do not have the logs, as explained in
the last email, I have no trace of the failure :( Note the tcpdump of
the hellos in both directions. I thought if the adjacency failed a
database update would be forced when it is re-established.
Oh BTW I checked my logs on the interfaces and the physicals have been
up all the time.
What's up with ospf?
Aidan
On Wed, 2007-12-05 at 01:00 -0800, Atanu Ghosh wrote:
> Hi,
>
> The output that it would be good to see before and after the problem
> occurs.
> 1) $ netstat -nr
> 2) Xorp> show interfaces
> 3) Xorp> show route table ipv4 unicast final
> 4) Xorp> show ospf4 neighbor detail
> 5) Xorp> show ospf4 database detail
> 6) $ print_lsas -S save.lsas
> The print_lsas program can be found in ospf/tools directory. The program
> stores the LSA database in a form that can be replayed.
>
> You can also enable tracing in ospf:
> traceoptions {
> flag {
> all {
> disable: false
> }
> }
> }
>
> Which should show routes being added and deleted.
>
> The latest code in CVS has a "clear ospf4 database" command, it would be
> interesting to know if once the problem occurs if this solves the
> problem.
>
> It might also be interesting to keep the "ip mon" command running to
> track routes being added and deleted.
>
> Would it be possible at some off peak time to flap the ADSL link to see
> if this replicates the problem. I know that you have stated that there
> were no ADSL issues when the problem occurred, but I do wonder if we are
> seeing some issue related to dynamic interfaces.
>
> Atanu.
>
> >>>>> "Aidan" == Aidan Walton <awalton at wires3.net> writes:
>
> Aidan> Hi, The adjacency runs over a wireless link between the
> Aidan> routers. It can, very possibly, drop in and out, but as far
> Aidan> as I can see this did not happen and to be honest in the 9
> Aidan> months I have had this system up I have never seen the
> Aidan> wireless link drop, but packet corruption could be a
> Aidan> possibility and this may be less easy to diagnose. It is a
> Aidan> high power 5.8GHz connection, here in the UK this is a
> Aidan> licensed band (and yes I have a license). So I don't think
> Aidan> interference is the likely cause, though I wouldn't rule this
> Aidan> out. If I look at the logs from the same period I seen
> Aidan> nothing to indicate the interface flapped, I would see the
> Aidan> wireless dis-associate and re-associate and cypher exchange
> Aidan> and this did not happen. But as I say there could be a period
> Aidan> of high BER on the links. I thought ospf would handle this
> Aidan> reasonably gracefully? I have to say heavy BER was not
> Aidan> evident when I came to repair the network, or at least I
> Aidan> didn't detect it and in the past I have run ospf over another
> Aidan> one of my wireless links with stations 10km apart with the
> Aidan> wireless link almost non-functional, dropping packets left
> Aidan> right and centre and re-associating over and over, but xorp's
> Aidan> ospf never complained! I was beginning to suspect that this
> Aidan> was related to my adsl link on the suspect router, as this is
> Aidan> a dynamic interface and I have this defined independently of
> Aidan> xorp. If this interface flaps then the default route
> Aidan> associated with the adsl ppp session is withdrawn. The
> Aidan> default from the adsl line is not propagated into ospf
> Aidan> though, instead I use a static default with a higher metric
> Aidan> pointed at the loopback and inject this into ospf
> Aidan> instead. Then the flaps of the adsl line do not cause churn
> Aidan> in the ospf domain. I was starting to think that the addition
> Aidan> and removal of the default from the adsl line was affecting
> Aidan> the kernel table and this was upsetting xorp's ospf. However
> Aidan> this morning when this happened the adsl line was stable. As
> Aidan> far as my logs look it suddenly decided to stop functioning
> Aidan> with no correlated events from other system processes. The
> Aidan> only things in the logs at the same time is iptables dropping
> Aidan> DOS attacks, but this in normal, unfortunately far to normal.
> Aidan> show ospf4 neighbour simply stated 'full' there is only one
> Aidan> neighbour defined on this router. I didn't look this time at
> Aidan> show interfaces, but from memory of the last time this
> Aidan> happened this also was normal. The problem is that these
> Aidan> routers are mounted 10m high up telegraph poles. If I loose
> Aidan> connectivity it requires a ladder and a climbing harness to
> Aidan> get at them, this is not to mention my upset customers who,
> Aidan> as is normal with customers, do not delay in telling me they
> Aidan> have lost their Internet links. I suppose what I'm trying to
> Aidan> understand is how to be best prepared for next time, logging,
> Aidan> processes and checks during the failure period to grab as
> Aidan> much useful info before I am forced to restart xorp and get
> Aidan> my customers up and running again. This is a very short
> Aidan> period I have to say. I have a small group of business units
> Aidan> supported on this router and all hell breaks loose if this
> Aidan> happens during working hours. How can I get the maximum
> Aidan> logging info from the xorp processes? Anything I can do in
> Aidan> order that you can help me, will be dutifully carried
> Aidan> out. What next, any suggestions? Thanks Aidan I will On Tue,
> Aidan> 2007-12-04 at 12:19 -0800, Atanu Ghosh wrote:
>
> Atanu> Hi,
>
> Atanu> The scenario that you describe would be perfectly normal if
> Atanu> the connectivity between the "suspect" router and the
> Atanu> "adjacent" router is lost. Although I would expect the "show
> Atanu> ospf4 neighbor" to show the state of the adjacency to be
> Atanu> "Down" not "Full". When an OSPF router loses its adjancencies
> Atanu> the LSA database will slowly timeout, however, the routes
> Atanu> will be withdrawn as soon as the adjacencies are lost.
>
> Atanu> We will require more information to diagnose the problem next
> Atanu> time the problem occurs the output of "show interfaces" and
> Atanu> "show ospf4 neighbor" would be very useful.
>
> Atanu> XORP tracks the state of interfaces in particular the carrier
> Atanu> state. If OSPF believes that the Ethernet has been
> Atanu> disconnected it will stop attempting to send hello
> Atanu> packets. Is it possible that there is a problem with an
> Atanu> interface or cable between the two routers?
>
> Atanu> Atanu.
>
> >>>>> "Aidan" == Aidan Walton <awalton at wires3.net> writes:
>
> Aidan> Hi All, I am using xorp in a production environment,
> Aidan> admittedly a small one. I operate a local WISP and xorp is
> Aidan> running on my wireless nodes. I have a very simple
> Aidan> configuration and really I could probably get away with
> Aidan> static routing throughout the entire network, but I wanted to
> Aidan> try xorp and see just how stable it was. However as I expand
> Aidan> the network I am having second thoughts. It is not good at
> Aidan> all when a network goes up in smoke and I can't explain why
> Aidan> or predict when and what the causes are. The network has
> Aidan> been in operation 24x7 for around 9 months. I am running on a
> Aidan> Linux kernel 2.6.18-4 and for the vast majority of the time I
> Aidan> have no issues. However now for the fourth time I see the
> Aidan> same problem: Suddenly the Linux kernel and the xorp rib
> Aidan> become detached. Normally all routes in the kernel match
> Aidan> those that xorp is generating, receiving and electing as
> Aidan> active. I am running OSPF and the neighbour states remain
> Aidan> 'full' throughout but if I am not mistaken I see ospf hellos
> Aidan> only in one direction (i.e nothing being transmitted from the
> Aidan> router I suspect). The lsdb of OSPF on the suspect and
> Aidan> adjacent routers contain all the routes but they are aging
> Aidan> out slowly on the adjacent router. When I look at the kernel
> Aidan> routes those from OSPF have already vanished. I can see the
> Aidan> ospf process running on the offending router? and again I can
> Aidan> see the ospf lsdb intact and correct. When I restart xorp the
> Aidan> system recovers and the routes appear in the kernel again. I
> Aidan> suspect a problem with ospf. I tried enabling traceoptions on
> Aidan> the ospf process, but in fact I needed to restart all the
> Aidan> xorp processes before this actually became active. I now have
> Aidan> this running so if/when it happens again I might be able to
> Aidan> offer some more information. Does anyone have any experience
> Aidan> of ospf begin unstable? any suggestions how I might more
> Aidan> effectively capture some logs from this event. I do not see
> Aidan> any options for logging the fea process. Is there anything I
> Aidan> can enable to help diagnose the issue? Many thanks, and of
> Aidan> course cheers for the code in the first place. Aidan
> Aidan> _______________________________________________ Xorp-users
> Aidan> mailing list Xorp-users at xorp.org
> Aidan> http://mailman.ICSI.Berkeley.EDU/mailman/listinfo/xorp-users
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