[c-nsp] Monitoring failed state of DSL / Cable (Ethernet)interfaces

[Brian Feeny]

Yes, very true.  What I do, is I policy route all traffic for the WAN 
interface IP's anyways.  I assume in the absense
of loopbacks, that SAA sources using the outgoing interface IP.   I 
policy route my WAN interface IP's out to the next
hop.

Brian

On Mar 2, 2005, at 7:29 AM, Rodney Dunn wrote:

> That's why with SAA you have to policy route
> the probe out the interface you want to monitor
> until SAA is enhanced to allow you to specify
> the exit interface explicitly.
>
> Rodney
>
> On Tue, Mar 01, 2005 at 04:44:19PM -0800, Ted Mittelstaedt wrote:
>>
>>
>>> -----Original Message-----
>>> From: cisco-nsp-bounces at puck.nether.net
>>> [mailto:cisco-nsp-bounces at puck.nether.net]On Behalf Of Dan Martin
>>> Sent: Tuesday, March 01, 2005 12:33 PM
>>> To: Brian Feeny; cisco-nsp
>>> Subject: RE: [c-nsp] Monitoring failed state of DSL / Cable
>>> (Ethernet)interfaces
>>>
>>>
>>> You may try "rping" on the router to ping some router upstream of the
>>> dsl modem.  When the poll fails, you take the message and use that to
>>> admin down the Ethernet interface on the router, thus triggering some
>>> switch over.
>>>
>>> Once its switched over, you will need to bring the interface back up 
>>> so
>>> you can keep pinging so you will know when the dsl line comes back to
>>> life.
>>>
>>
>> That won't work because as soon as the line is switched over the pings
>> will start working again - since they now will be routed around 
>> through
>> the backup link.
>>
>> ALL of the commercial solutions I've seen that use DSL for a primary
>> assume PPP-mode DSL.  If the DSL line goes down the PPP packets don't
>> come in anymore and it is easy for the router to understand that the
>> DSL line went away.
>>
>> If it's bridged DSL then one way is to set your script up to ping the
>> default gateway on the DSL side then check for the existence of the
>> MAC address in the arp table for that IP number.  If it isn't there 
>> then
>> you know the DSL line is down and you can rewrite the default route.
>> And when the DSL line comes back you will know because the ARP will
>> reappear.
>> Unfortunately this is beyond the capabilities of Cisco routers.
>>
>> Running OSPF out both interfaces would be a better way to do it.  That
>> would require the provider to support it, though.
>>
>> Ted
>>
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