<div dir="ltr"><br><div>There's a number of ways to test L1/L2, it's less about wanting to check that a route target is at the other end, as it is about detecting misconfigurations, spanning tree problems or cable/connection problems such as uni-directional link.</div>
<div> - The many variations of Spanning Tree Protocol</div>
<div> - Uni-Directional Link Detection</div><div> - LACP/PAgP</div><div> - Bi-directional Forwarding Detection<br></div><div><br></div><div>Probably others that I don't know about.</div><div><br></div><div>CDP (and LLDP) are (insecure and unreliable) informational protocols only. They don't tell you anything more than what *might be* at the other end of the link and they can't do anything more than that unless you're in user land with PoE handsets.</div>
<div><br></div><div>The original poster is talking static L3 routes on Cisco equipment. The resulting status of object tracking from IP SLA tests against the gateway address is the best way of handling the problem.</div>
<div><br></div><div>That all said: The **EXACT** issue that has been posed is 50% of the reason dynamic routing was first created.</div><div><br></div><div>-Colin</div><div class="gmail_extra">
<br><br><div class="gmail_quote">On 5 May 2014 16:23, Joshua D'Alton <span dir="ltr"><<a href="mailto:joshua@railgun.com.au" target="_blank">joshua@railgun.com.au</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<p dir="ltr">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?</p>
<p dir="ltr">sent from android</p><div class="HOEnZb"><div class="h5">
<div class="gmail_quote">On 05/05/2014 4:15 PM, "Chris Balmain" <<a href="mailto:chris@team.dcsi.net.au" target="_blank">chris@team.dcsi.net.au</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<font face="Helvetica, Arial, sans-serif">Erm... meant to say
ARP/ping reachability verification is *not* used unless you tell
it to...<br>
<br>
</font>
<div>On 05/05/14 16:12, Chris Balmain wrote:<br>
</div>
<blockquote type="cite">
<font face="Helvetica, Arial, sans-serif"><font face="Helvetica,
Arial, sans-serif">T</font>he 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)<br>
<br>
ARP/ping reachability verification is used unless you tell it to
(on Cisco via "ip sla" -
<a href="http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/813-cisco-router-ipsla-basic.html" target="_blank">http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/813-cisco-router-ipsla-basic.html</a>)<br>
<br>
CB<br>
<br>
</font>
<div>On 05/05/14 15:58, Alex Samad -
Yieldbroker wrote:<br>
</div>
<blockquote type="cite">
<pre>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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</blockquote>
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</blockquote>
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