BFD dampening

[lionell01]

hello. We're looking to implement interface (IP event) and BFD dampening.

We currently have BFD being tracked by BGP as well as BGP route dampening in place :

interface te1/1/1

bfd interval 700 min_rx 700 multiplier 3

router bgp 65000

bgp dampening

neighbor 10.10.10.1 fall-over bfd

1. Will implementing both IP event + BFD dampening help in any way or is just one enough?
2. What is the exact configuration for BFD dampening?

Have found the below :

1. enable
2. configure terminal
3. bfd-template multi-hop TEST-BFD-TEMPLATE
4. interval min-tx milliseconds min-rx milliseconds multiplier multiplier-value
5. dampening [ half-life-period reuse-threshold suppress-threshold max-suppress-time]
6. Since our neighbour is one hop away (P2P link) will the template type be single hop?
7. The documentation does not mention this but I’ve found that the template needs to be applied to the interface

interface te1/1/1

bfd template TEST-BFD-TEMPLATE

1. Will this template command replace the “bfd interval” command?
2. Or will this be a different BFD session altogether which means my neighbour will also need to configure the same?

Apologies, the documentation isn’t really robust on this topic.

[David Ruess]

Hello,

See if the document below helps you out:

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bfd/configuration/xe-16/irb-xe-16-book/irb-bfd-damp.html

-David

[lionell01]

hi David,

This is the doc I originally referred. It has really limited information.

[David Ruess]

OK so lets break it down.

First off that documentation is limited because its a small feature of BFD. Here is the beginning doc for BFD which should be understood before configuring other features:

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bfd/configuration/xe-16/irb-xe-16-book/irb-bi-fwd-det.html

So you have BFD and BGP dampening. Understand that these do 2 very different things. The BFD dampening is focused on the link/connectivity. So if it loses link/connectivity then the BFD will kick in. This does not mean if you lose the BGP neighbor. The neighbor can be lost and the link would still be up.

BGP dampening is concerned with BGP routes/updates. So even if the link doesn't go down but maybe a BGP neighbor is still having issues with routes flapping up and down and sending updates every time that happens. On a slower link this could be problematic (its problematic regardless but the slower link amplifies the effect). SO they are needed for different reasons.

To answer the BFD template question look at it like this. If you have 10 links that you need to apply the same BFD configuration to instead of configuring individual links you would apply the configuration to a template and apply that template to an interface, or in this case....10 interfaces.

-Hope that helps.

[lionell01]

Hi David, Thanks for your response. My query is mainly with respect to whether both IP event dampening & BFD dampening need to be implemented together (IMO one would be enough).

And also I need help with implementing BFD dampening. 

[David Ruess]

OK I think I understand a bit better. Lets break it down:

IP Event dampening is Protocol Independent route dampening mechanism, whereas BGP has its own dampening mechanism. Look at it like this. Each routing protocol has its hello/dead timers. That's protocol specific. BFD comes in and you can attach the protocol to the BFD session to track interface status and NOT wait for the hello timers. That's protocol Independent because its not tied to a specific protocol and it supports many of them. So IP even dampening is protocol independent (maybe you have several routing protocols running on a device) and you can use that. Or you can use the protocol specific dampening like you have in BGP. I dont know your whole environment so I cant make that decision.

As far as the BFD dampening it looks like its only supported in template configuration. So you need to take your existing interface configuration and add it to a template along with the dampening option and apply that template to the interface.

As far as what times you need set that will be specific to your organization and needs. I would get with them to determine whats best. I would not listen to strangers on the internet about specific timers/specifications to implement in your organization. 

For configuration you just need to follow steps 1-5 on the doc I sent first.

config t
bfd-template {multi-hop | single-hop} <name>
bfd interval 700 min_rx 700 multiplier 3
dampening <insert your company policy values>
end
wr mem

Hope that clears more of it up.

[MHM Cisco World]

I will run lab and share you update 

[MHM Cisco World]

I run lab 
use BGP between two peers, 
disable direct check in BGP 
run BGP with fall over bfd single-hop 
I use bfd template with dampening, 
but I failed to get flapping and make BFD dampening work, 

but from my view using BGP dampening is same as using IP SLA with BGP EEM, 
we can use track IP SLA to detect neighbor status, this IP SLA timer can adjust to detect the neighbor dead according to freq and timeout setting. 
these IP SLA feature we can use instead bfd dampening. 

now the Q, what value we will use ?
this more hard to answer, but I prefer the cisco default value. 

[lionell01]

Thanks, the values are something we can determine along with our customer. However, like you, even I couldn't get it to work in GNS3. Just wanted to ensure the configuration is correct.

[madhansansel]

Q1: Will this template command replace the “bfd interval” command?

"bfd interval" command is the legacy one. If we use "bfd interval" command, then BFD echo is enabled by default. But in bfd template command, "bfd echo" is not enabled by default. Many BFD features, for example bfd dampening etc  are implemented using BFD template command. Hence it is recommended to use "bfd template" command.

Q2: Or will this be a different BFD session altogether which means my neighbour will also need to configure the same?

We can use bfd template command in one end and bfd interval command in the other end. But it is recommended to use bfd template command. Because many features are supported in template.