Newbie Concern: (BGP) AS-Path Oscillation
Dear Guru(s), My apologies upfront if this question has already been asked. If that’s the case, please kindly point me to the solution|thread so that the mailing list bandwidth is not wasted. Situation: On one of our prefixes, we are detecting continuous “BGP AS-Path Changes” in the order of 1,000 announcements per hour---practically one every 3-4 seconds. Those paths oscillate between two of our immediate upstreams. Questions: 1. Is this number of events “normal” for a prefix? 2. Is there any way we, as the tail-end (Origin Announcer), can do to reduce it? Or should I just “let it be”? 3. [Extra] Is this kind of oscillation affecting user experience, say, throughput and/or latency? Thank you in advance for all the pointers and help. Best Regards, Pirawat.
I don't think this is normal, I think this is a fault and needs to be addressed. There should be significant reachability problems, because rerouting isn't neither immediate, nor lock-step with SW+HW nor synchronous between nodes. What exactly needs to be done, I can't tell without looking at the specific case. I'm not sure I understand 'tail-end ' and 'origin announcer' as synonyms, tail to me means receiver, head advertiser. But origin announcer to me means advertiser. So I'm not sure in which position you are. But if you are the source of this prefix, then you can probably fix the situation, if you are not, then you probably cannot fix the situation. On Mon, 28 Nov 2022 at 07:56, Pirawat WATANAPONGSE via NANOG <nanog@nanog.org> wrote:
Dear Guru(s),
My apologies upfront if this question has already been asked. If that’s the case, please kindly point me to the solution|thread so that the mailing list bandwidth is not wasted.
Situation: On one of our prefixes, we are detecting continuous “BGP AS-Path Changes” in the order of 1,000 announcements per hour---practically one every 3-4 seconds. Those paths oscillate between two of our immediate upstreams.
Questions: 1. Is this number of events “normal” for a prefix? 2. Is there any way we, as the tail-end (Origin Announcer), can do to reduce it? Or should I just “let it be”? 3. [Extra] Is this kind of oscillation affecting user experience, say, throughput and/or latency?
Thank you in advance for all the pointers and help.
Best Regards,
Pirawat.
-- ++ytti
On Sun, Nov 27, 2022 at 9:52 PM Pirawat WATANAPONGSE via NANOG <nanog@nanog.org> wrote:
On one of our prefixes, we are detecting continuous “BGP AS-Path Changes” in the order of 1,000 announcements per hour---practically one every 3-4 seconds. Those paths oscillate between two of our immediate upstreams.
Hi Pirawat, What are they changing -from- and what are they changing -to-? I.e. what are the actual RIB entries in your routing table. Not merely the selected one, but all of the RIB entries known to your router for that route at each stage of the oscillation. It's hard to say whose bug it is without digging a little deeper. It might be your bug. It's also hard to say whether the fault is user-impacting without doing that sort of basic diagnosis.
2. Is there any way we, as the tail-end (Origin Announcer), can do to reduce it?
BGP route flap damping, sometimes incorrectly called route dampening if you're trying to search for it. Regards, Bill Herrin -- For hire. https://bill.herrin.us/resume/
[ i would have written privately except the damned dmark crap obscured your email address. grrrrr. ]
On one of our prefixes, we are detecting continuous “BGP AS-Path Changes” in the order of 1,000 announcements per hour---practically one every 3-4 seconds.
where is this being 'detected?' i.e. from what vantage point? is it safe to assume that your outbound announcements to your two upstreams are stable? of course, if you would care to divulge a prefix showing this symptom, folk might be able to find clues. randy --- randy@psg.com `gpg --locate-external-keys --auto-key-locate wkd randy@psg.com` signatures are back, thanks to dmarc header butchery
participants (4)
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Pirawat WATANAPONGSE -
Randy Bush -
Saku Ytti -
William Herrin