Disappearing default route
Bela Gazdy
week ago the default route suddenly disappeared. It is still in the ODM, with
consistent showings by
'lsattr -E -l inet0' and 'odmget -q attribute=route CuAt'
When I add it back again by either
'mkdev -q -l inet0' or 'chdev -T -l inet0 -a route=...'
it shows up in the output of 'netstat -rn', and connectivity to outside of the
sub-net is restored; however, in a few minutes (2-3mins) it disappears again.
The only NIC is an IBM 10/100 Mbps Ethernet PCI Adapter, and we do not run
"fancy" stuff, like DHCP or HACMP/Clusters. AIX version is 5300-10-01-0921.
This might be a coincidence, but....
About the same time when the default route started vanishing, error log
started shownig sporadic
'SYSXAIXIF DUPLICATE IP ADDRESS DETECTED IN THE NET'
entries. To me, this indicates a rogue/mis-configured DHCP server hijacking
my IP. I have tried unplugging the Ethernet cable, but the default route
disappears just the same. We are in a process to identifying the rouge server.
Something wipes out the default route, but what? I have tried from deleting
the device to rebooting the box, to no avail.
Any advice or idea how to further diagnose the problem or what the root cause
might be, would be highly appreciated. Thank you, -Bela.
Hajo Ehlers
> I have an old 44P 270 and it has been working flawlesslly for years. About a
> week ago the default route suddenly disappeared. It is still in the ODM, with
> consistent showings by
>
> 'lsattr -E -l inet0' and 'odmget -q attribute=route CuAt'
>
> When I add it back again by either
>
> 'mkdev -q -l inet0' or 'chdev -T -l inet0 -a route=...'
>
> it shows up in the output of 'netstat -rn', and connectivity to outside of the
> sub-net is restored; however, in a few minutes (2-3mins) it disappears again.
>
Maybe DGD ( dead gateway detection ) comes into play ?
Can be checked with the no command
$ no -a | grep dgd
$ no -o passive_dgd
# passive_dgd = 0
# 0 = active )
which notes that the routed or gated might also change the route if
configured. Thus check whether one of the daemons are used or not.
From my understanding DGD will set a route ( disabling it ) down in
case it can not reach the gateway - because in your case of the
duplicate IP address . Thus get the node using your IP and/or
reconfigure DGD to work in passive mode and/or set dgd parameter in
such a way that DGD does not hit you even in case of a dup IP
address..
See also - in case you hit a DGD bug like this:
IZ43864: ACTIVE DGD FAILS TO RE-SET MAX FOR HIGHER COST ROUTES
http://www-01.ibm.com/support/docview.wss?rs=0&q1=IZ43864&uid=isg1IZ43864
hth
hajo
Bela Gazdy
HE>On Mar 1, 1:35 pm, Bela Gazdy <b...@bluedog.cc.emory.edu> wrote:
>> I have an old 44P 270 and it has been working flawlesslly for years. About
>> a week ago the default route suddenly disappeared. It is still in the ODM,
>> with consistent showings by
>>
>> 'lsattr -E -l inet0' and 'odmget -q attribute=route CuAt'
>>
>> When I add it back again by either
>>
>> 'mkdev -q -l inet0' or 'chdev -T -l inet0 -a route=...'
>>
>> it shows up in the output of 'netstat -rn', and connectivity to outside of
>> the sub-net is restored; however, in a few minutes (2-3mins) it disappears
>> again.
>>
HE>Maybe DGD ( dead gateway detection ) comes into play ?
HE>
HE>Can be checked with the no command
HE>
HE>$ no -a | grep dgd
HE>$ no -o passive_dgd
HE># passive_dgd = 0
HE># 0 = active )
HE>
HE>See
HE>http://publib.boulder.ibm.com/infocenter/aix/v6r1/index.jsp?topic=/com.ibm.aix.commadmn/doc/commadmndita/tcpip_routing_gtwy_detect.htm
HE>
HE>which notes that the routed or gated might also change the route if
HE>configured. Thus check whether one of the daemons are used or not.
HE>
HE>From my understanding DGD will set a route ( disabling it ) down in
HE>case it can not reach the gateway - because in your case of the
HE>duplicate IP address . Thus get the node using your IP and/or
HE>reconfigure DGD to work in passive mode and/or set dgd parameter in
HE>such a way that DGD does not hit you even in case of a dup IP
HE>address..
HE>
HE>See also - in case you hit a DGD bug like this:
HE>IZ43864: ACTIVE DGD FAILS TO RE-SET MAX FOR HIGHER COST ROUTES
HE>http://www-01.ibm.com/support/docview.wss?rs=0&q1=IZ43864&uid=isg1IZ43864
HE>
HE>hth
HE>hajo
Thanks, Hajo!
To configure DGD, don't we need a multi-homed system, that is one with two
or more NICs or two or more VIPs? Ours is a One-NIC-One-IP box. Please,
let me know if (when) I am wrong.
Thank you,
-Bela
Hajo Ehlers
...
>
> To configure DGD, don't we need a multi-homed system, that is one with two
> or more NICs or two or more VIPs? Ours is a One-NIC-One-IP box. Please,
> let me know if (when) I am wrong.
>
All AFAIK - DGD works right out of the box. Since you can have
multiply routes on one NIC using no aliases ( One IP) it does not
matter IMHO that you have only one NIC with one IP configured.
But your real problem is not your lost route but the double IP address
in your network.
cheers
Hajo
Bela Gazdy
HE>On Mar 1, 4:57 pm, Bela Gazdy <b...@bluedog.cc.emory.edu> wrote:
HE>...
>>
>> To configure DGD, don't we need a multi-homed system, that is one with two
>> or more NICs or two or more VIPs? Ours is a One-NIC-One-IP box. Please,
>> let me know if (when) I am wrong.
>>
HE>All AFAIK - DGD works right out of the box. Since you can have
HE>multiply routes on one NIC using no aliases ( One IP) it does not
HE>matter IMHO that you have only one NIC with one IP configured.
HE>
HE>But your real problem is not your lost route but the double IP address
HE>in your network.
HE>
HE>cheers
HE>Hajo
HE>
It has turned out that it was a faulty NIC, although it passed HW diagnostics
with flying colors. All the mangled network behavior, including the Dupe IP
errors, was the artifact of some stray electrons... :-(