Classification:Internal
Hi Mark,
Thanks for the update. You have any backhauls, that is running over an L2
xconnect ? I’m facing issue only on the backhaul link over a l2vpn ckt.
Ta,
From: NANOG On
Behalf Of Mark Tinka
Sent: Thursday, July 16, 2020 8:35 PM
To: nanog@nanog.org
Subject: Re: BFD for long haul circuit
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On 16/Jul/20 05:51, Harivishnu Abhilash wrote:
Classification:Public
Guys, I’m looking for recommendation regarding BFD timers that we can use for
long haul circuit. RTT is roughly around 110 ms. In fact this is a l2vpn ckt
provided by a telco.
Can you please advise the factors we can consider when setting the BFD timers
(or any recommended values)? I have set 10 ms dead time but this is causing BFD
to go down occasionally.
We run different intervals and multipliers depending on whether the connection
is LAN or WAN.
For LAN (so within the same data centre), intervals are set to 150ms and
multipliers are set to 3.
For WAN (any backbone regardless of latency), intervals are set to 250ms and
multipliers are set to 5.
Since our network spans multiple countries and continents, we wanted a uniform
value for the WAN side of things, so we don't have too many customized
configurations. We found these settings to work well in mixed environments
where implementations vary between CPU and line card processing, and also to
strike a balance between accuracy and false positives.
We've been running this on IOS XE, IOS XR and Junos platforms since 2014. The
only issues we found were:
* BFD on LAG's on IOS XR platforms in a LAN environment don't work. A
point-to-point mechanism is required, so we disabled it there. Junos and IOS XE
have no problems running BFD on LAG's in LAN's, so we have it on there. This is
for within the data centre.
* BFDv6 on the MX does not run in hardware. Since IS-IS (for us) ties in
BFD for link state event detection, a transient lack of CPU resources to
service BFDv6 traffic will result in not only BFDv6 going down, but also the
entire IS-IS protocol flapping on the assumption that a link event has
occurred. So if you run BFDv6 alongside BFDv4, recommend that you disable BFDv6
until Juniper introduce hardware support for it on the MX (and I'm guessing all
other Junos platforms). We have an ER out for this since 2019, and we are told
it should be appearing sometime between Q4'20 - 1H'21.
* Syntax for BFD in Junos has changed to incorporate address families. So
while the old syntax will commit, it will leave an annotation in the
configuration about not being supported anymore. Recommend you convert your
Junos BFD configurations to IPv4 and IPv6 specificity, if you haven't already
done so. I can't remember when this came into effect, but it likely was Junos
16. We are on Junos 17 now.
Our longest circuit point-to-point is 140ms (Cape Town - London). These
settings have been running fine on there since Day 1 (IOS XR-to-IOS XR), and
overall detection and re-convergence of IS-IS + LFA leaves us happy and
sleeping well at night.
Mark.
This email is classified as Internal by Harivishnu Abhilash
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