[Xorp-users] Problems with Linux kernel and OSPF ???
Atanu Ghosh
atanu at ICSI.Berkeley.EDU
Wed Dec 5 01:00:53 PST 2007
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
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