[TriLUG] some TCP utilities ignore kernel routing table?

[Shane O'Donnell]

Likely a problem with a bad entry in the kernel's route cache.

Try:  route -n
Then:  route -nC

I've seen this before and have no recollection as to why it happened
-- for some reason, I'm remembering Nortel Passport switches were
involved, but not necessarily isolated as "at fault".

Perhaps the good senator from Charlotte, NC, the honorable Michael
Johnson might recall...

You can flush the kernel's route cache by echoing a "1" to
/proc/sys/net/ipv4/route/flush, if memory serves.  Probably do well to
verify that with a Google search before proceeding -- that might also
be the "make this box ignite" switch...

Shane O.

On 1/10/06, Tanner Lovelace <clubjuggler at gmail.com> wrote:
> On 1/10/06, Brian Henning <brian at strutmasters.com> wrote:
> > Hi Folks,
> >    Just wondering if someone could shed some light on why it seems that
> > some tcp utilities seem to ignore the kernel routing table.  For
> > example:  (Sorry about the wrapping..)
> >
> > % /sbin/route -n
> > Kernel IP routing table
> > Destination     Gateway         Genmask         Flags Metric Ref    Use
> > Iface
> > 192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
> > 192.168.10.0    192.168.1.125   255.255.255.0   UG    0      0        0 eth0
> > 0.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0 eth0
> >
> > % telnet 192.168.10.4
> > Trying 192.168.10.4...
> > telnet: Unable to connect to remote host: No route to host
> >
> > Um.  Yes there is a route to the host.  Right there in the kernel
> > routing table.  It says to go by way of .1.125.
> >
> > What gives?  I think this also affects the cups printing manager as it
> > does nothing but report no printer at the specified address/port.
>
> 1. Have you actually verified that you can reach .1.125?
> 2. Try a traceroute to 192.168.10.4.
> 3. Try a ping to 192.168.10.4.
>
> Report back.
>
> Cheers,
> Tanner
> --
> Tanner Lovelace
> clubjuggler at gmail dot com
> http://wtl.wayfarer.org/
> (fieldless) In fess two roundels in pale, a billet fesswise and an
> increscent, all sable.
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--
Shane O.
========
Shane O'Donnell
shaneodonnell at gmail.com
====================