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Hi Scott,
<div class="">BFD isn't line state - BFD is a negotiated session between 2 routers; it is the attached to a protocol like OSPF or BGP. As BFD operates on the data plane then signals the control plane protocol (OSPF, BGP etc) - when BFD detects link loss or
packet loss, it will signal to immediately tear down the routing protocol on that interface - and as BFD is configured on both sides of a link - both sides will tear down resulting in outages well under 1 second when convergence of tables can be achieved this
fast.</div>
<div class="">From my experience, when the BGP "update-source" changes state to "down" - most (i use this term carefully) platforms will drop the routing protocol session - but thats not to say that both sides of a BGP session will see this interface transition
and behave the same - i.e. IX networks.</div>
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<div class="">Hi Alex,</div>
<div class="">On my convergence point there - when tables can be converged that fast - if your hardware (or software) router could not converge routing tables fast enough you would have experienced something like this. What are you routing on? (hit me up offlist
if this is sensitive).</div>
<div class="">It could also be configuration related - (a) on your gear, a second pair of eyes (usually) never hurts - (b) with a second provider, i have suffered URPF issues with some upstreams in the past when traffic failed over to them due to a non updated
configuration their side.</div>
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<div class="">Tom<br class="">
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<div class="">On 27 Jan 2015, at 11:48 pm, Scott O'Brien <<a href="mailto:scott@scottyob.com" class="">scott@scottyob.com</a>> wrote:</div>
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<div class="">I can see how BFD and lower hold & keep-alive messages help convergence time (obviously) but am wondering how useful it is in practice? Do most people peer with a directly connected interface on routers or through an intermediate switch? I would
be expecting most would peer with their providers using links on the router itself and would be taking advantage of the (on by default in Cisco world) fast-external-fallover. Obviously this relies on the interface going down (so wouldn’t work with Transit
over Megaport for instance or switch in between) and doesn’t help a dying control plane issue but wouldn’t the default behaviour be pretty good in helping convergence in most typical eBGP setups & failures with this feature?</div>
<div class=""><br class="">
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<div class="">~ Scotty O</div>
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<div class="">
<blockquote type="cite" class="">
<div class="">On 27 Jan 2015, at 11:19 pm, Alex Samad - Yieldbroker <<a href="mailto:Alex.Samad@yieldbroker.com" class="">Alex.Samad@yieldbroker.com</a>> wrote:</div>
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<span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class="">Hi<o:p class=""></o:p></span></div>
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<span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class=""> </span></div>
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<span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class="">I will have to monitor that. <o:p class=""></o:p></span></div>
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<span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class="">We suffered from an outage recently, with a provider we have 2 links with. We have multiple providers.<o:p class=""></o:p></span></div>
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<span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class="">As a review of the incident the business asked about the 3m hold timer. In theory the way I read it, is the routes could be held for up to 3 min whilst the link
is down…<o:p class=""></o:p></span></div>
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<span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class="">One of the questions was why did it take soo long ~ 8-9min for traffic to appear on the other link. Waiting for feedback on that<o:p class=""></o:p></span></div>
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<span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class="">I am presuming with a lower hold timer/keep alive I can get pretty fast response as its only on this providers network I am failing over.<o:p class=""></o:p></span></div>
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<span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125);" class="">Alex<o:p class=""></o:p></span></div>
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<b class=""><span lang="EN-US" style="font-size: 10pt; font-family: Tahoma, sans-serif;" class="">From:</span></b><span lang="EN-US" style="font-size: 10pt; font-family: Tahoma, sans-serif;" class=""><span class="Apple-converted-space"> </span>Tom Berryman
[<a href="mailto:Tom@connectivityit.com.au" style="color: purple; text-decoration: underline;" class="">mailto:Tom@connectivityit.com.au</a>]<span class="Apple-converted-space"> </span><br class="">
<b class="">Sent:</b><span class="Apple-converted-space"> </span>Tuesday, 27 January 2015 11:09 PM<br class="">
<b class="">To:</b><span class="Apple-converted-space"> </span>Alex Samad - Yieldbroker<br class="">
<b class="">Cc:</b><span class="Apple-converted-space"> </span>David Hughes;<span class="Apple-converted-space"> </span><a href="mailto:ausnog@lists.ausnog.net" style="color: purple; text-decoration: underline;" class="">ausnog@lists.ausnog.net</a><br class="">
<b class="">Subject:</b><span class="Apple-converted-space"> </span>Re: [AusNOG] BGP hold timer values<o:p class=""></o:p></span></div>
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<o:p class=""> </o:p></div>
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There is a bit more than just a few extra packets (as your cost) - BGP can/does have notable CPU impact on low-mid range routing gear.<o:p class=""></o:p></div>
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With eBGP, you are talking propagation of your routes to the internet, so not all of the internet is going to see your changes for maybe up to 180 seconds. That said, it's likely most of it will be sooner than that.<o:p class=""></o:p></div>
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Tom<o:p class=""></o:p></div>
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On 27 Jan 2015, at 11:01 pm, Alex Samad - Yieldbroker <<a href="mailto:Alex.Samad@yieldbroker.com" style="color: purple; text-decoration: underline;" class="">Alex.Samad@yieldbroker.com</a>> wrote:<o:p class=""></o:p></div>
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<o:p class=""> </o:p></div>
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Hi<br class="">
<br class="">
Okay its eBGP, currently have 4 providers, some with multiple connections. So I am thinking 6 / 20 might be good for me, business requirement for approx. 30sec response.<br class="">
I am presuming all I am looking at is extra BGP packets .. every 6 sec compared to 1 min..<br class="">
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<br class="">
Alex<br class="">
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-----Original Message-----<br class="">
From: David Hughes [<a href="mailto:david@hughes.com.au" style="color: purple; text-decoration: underline;" class="">mailto:david@hughes.com.au</a>]<br class="">
Sent: Tuesday, 27 January 2015 9:37 PM<br class="">
To: Alex Samad - Yieldbroker<br class="">
Cc:<span class="Apple-converted-space"> </span><a href="mailto:ausnog@lists.ausnog.net" style="color: purple; text-decoration: underline;" class="">ausnog@lists.ausnog.net</a><br class="">
Subject: Re: [AusNOG] BGP hold timer values<br class="">
<br class="">
<br class="">
I gave a lightning talk about this sort of thing a while ago at an APRICOT. I just<br class="">
googled to find the slides and can now see just how many years ago it was.<br class="">
Gotta say I'm feeling old :)<br class="">
<br class="">
But, it's probably still relevant although the defaults may have changed. This<br class="">
reflected what we were running at the time - and we were trying to be<br class="">
pretty aggressive.<br class="">
<br class="">
<a href="http://archive.apnic.net/meetings/21/docs/sigs/routing/routing-" style="color: purple; text-decoration: underline;" class="">http://archive.apnic.net/meetings/21/docs/sigs/routing/routing-</a><br class="">
pres-hughes-bgp.pdf<br class="">
<br class="">
For reference I'm currently happy to run<br class="">
<br class="">
eBGP<span class="apple-tab-span"><o:p class=""></o:p></span></div>
<div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;" class="">
: 10 / 30<br class="">
iBGP<span class="apple-tab-span"><o:p class=""></o:p></span></div>
<div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;" class="">
: 5 / 15<br class="">
<br class="">
And I'd run this even to a single upstream. If it fails at least you'll have<br class="">
something in your logs to say why you fell off the net for a while. Silent<br class="">
failures are a bugger to troubleshoot.<br class="">
<br class="">
<br class="">
Thanks<br class="">
<br class="">
David<br class="">
...<br class="">
<br class="">
<br class="">
<br class="">
On 27/01/2015, at 6:47 PM, Alex Samad - Yieldbroker<br class="">
<<a href="mailto:Alex.Samad@yieldbroker.com" style="color: purple; text-decoration: underline;" class="">Alex.Samad@yieldbroker.com</a>> wrote:<br class="">
<br class="">
<br class="">
<o:p class=""></o:p></div>
<div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;" class="">
Hi<br class="">
<br class="">
I'm wonder what is considered "best practice" or good/responsible hold<o:p class=""></o:p></div>
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timer values for BGP.<br class="">
<br class="">
<o:p class=""></o:p></div>
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<br class="">
Currently I'm set at 3m, but I am considering lowering this to 30s and keep<o:p class=""></o:p></div>
<div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;" class="">
alive down to 20s, potentially even lower. Or if possible to use BFD & BGP,<br class="">
what's the uptake on BFD ?<br class="">
<br class="">
<o:p class=""></o:p></div>
<div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif;" class="">
<br class="">
Alex<br class="">
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