[AusNOG] IOS router selection

[Chris Balmain]

Perhaps. I don't know if you can use it with IP SLA objects though, and 
the gateway device may not implement CDP, or may have it turned off - I 
know I always try to switch it off on untrusted (customer-facing) 
interfaces because it discloses things (e.g. IOS version) that could be 
used against you!

On 05/05/14 16:23, Joshua D'Alton wrote:
>
> seems to me CDP would be used/useful for this? At least from a l2 
> perspective which would be the case of outage 99% the time?
>
> sent from android
>
> On 05/05/2014 4:15 PM, "Chris Balmain" <chris at team.dcsi.net.au 
> <mailto:chris at team.dcsi.net.au>> wrote:
>
>     Erm... meant to say ARP/ping reachability verification is *not*
>     used unless you tell it to...
>
>     On 05/05/14 16:12, Chris Balmain wrote:
>>     The route is installed in the FIB if the router has a route to
>>     the gateway itself (e.g. via a connected interface in up/up
>>     status, or recursively via IGP etc)
>>
>>     ARP/ping reachability verification is used unless you tell it to
>>     (on Cisco via "ip sla" -
>>     http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/813-cisco-router-ipsla-basic.html)
>>
>>     CB
>>
>>     On 05/05/14 15:58, Alex Samad - Yieldbroker wrote:
>>>     Hi
>>>
>>>     I am looking for some documentation that explains the way cisco behaves.
>>>
>>>     If I have this
>>>
>>>     IOS
>>>     ip route 0.0.0.0 0.0.0.0 w.x.y.z 230
>>>     ip route 0.0.0.0 0.0.0.0 f.g.h.i  240
>>>     ip route 0.0.0.0 0.0.0.0 r.s.t.u 250
>>>
>>>     ASA
>>>     route internet 0.0.0.0 0.0.0.0 w.x.y.z 230
>>>     route internet 0.0.0.0 0.0.0.0 f.g.h.i 240
>>>     route internet 0.0.0.0 0.0.0.0 r.s.t.u 250
>>>
>>>
>>>     this tells me the default gateway used is w.x.y.z, unless that gateway is unavailable or dead..
>>>
>>>     I am looking at how Cisco decides when a gateway is dead, I found documents on route selection, but nothing that specifically address dead gateways
>>>
>>>     I presume, and from what I have seen if there is no arp its dead..
>>>
>>>     Thanks
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>>
>
>
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