[j-nsp] Carrier interfaces and hold timers

[Jonathan Call]

Anyone have experience with hold timers?


For the first time in my experience I have a carrier asking me to implement 3 second hold timers on their interface to deal with their link constantly flapping. They're citing this document as proof that it needs to be done:

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/hold-time-edit-interfaces.html

I'm extremely dubious of this requirement since I've never had a carrier ask for this and our router is a pretty old MX80 which does not have a lot of buffer space. But then again, maybe packet drops due to buffer overflow are better than carrier transitions and the resulting BGP teardown and rebuild.

Regards,

Jonathan


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[Olivier Benghozi]

In some cases, we have used holdtimers to wait before setting up the interface, but never before setting down it (if it's down, it's down, there are technologies to fast reroute).
But a link is not expected to flap in normal case. If it flaps, it's broken (and we all know it happens).

This being said, if you have a carrier explaining that you should expect only crap from them, you should:
- name and shame ;
- throw their services away ;
because they are clearly playing you for a sucker.


About the MX80: it doesn't lack buffer space, it lacks RAM and CPU.

Post by Jonathan Call
Anyone have experience with hold timers?
https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/hold-time-edit-interfaces.html
I'm extremely dubious of this requirement since I've never had a carrier ask for this and our router is a pretty old MX80 which does not have a lot of buffer space. But then again, maybe packet drops due to buffer overflow are better than carrier transitions and the resulting BGP teardown and rebuild.

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[Luis Balbinot]

Sometimes carriers protect optical circuits using inexpensive optical
switches that have longer switching delays (>50ms). In these cases I'd
understand their request for a longer hold-time. But 3 seconds is a lot.

Post by Jonathan Call
Anyone have experience with hold timers?
For the first time in my experience I have a carrier asking me to
implement 3 second hold timers on their interface to deal with their link
constantly flapping. They're citing this document as proof that it needs to
https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/hold-time-edit-interfaces.html
I'm extremely dubious of this requirement since I've never had a carrier
ask for this and our router is a pretty old MX80 which does not have a lot
of buffer space. But then again, maybe packet drops due to buffer overflow
are better than carrier transitions and the resulting BGP teardown and
rebuild.
Regards,
Jonathan
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[Olivier Benghozi]

That's not the point here ; the point here is:
«to deal with their link constantly flapping».

A constantly flapping link must be either fixed or cancelled.

Post by Luis Balbinot
Sometimes carriers protect optical circuits using inexpensive optical
switches that have longer switching delays (>50ms). In these cases I'd
understand their request for a longer hold-time. But 3 seconds is a lot.

Post by Jonathan Call
For the first time in my experience I have a carrier asking me to
implement 3 second hold timers on their interface to deal with their link
constantly flapping.

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