RE: Cisco ASR9902 SNMP polling ... is interesting

[Drew Weaver via NANOG <nanog () lists nanog org>]

They have the configuration. They seem to be saying that there is just some invisible hand inside the router 
controlling the responses on a per interface basis.

It’s pretty heavy handed tbh.

-Drew


From: Arie Vayner <ariev () vayner net>
Sent: Friday, August 1, 2025 10:15 AM
To: North American Network Operators Group <nanog () lists nanog org>
Cc: Mel Beckman <mel () beckman org>; Drew Weaver <drew.weaver () thenap com>
Subject: Re: Cisco ASR9902 SNMP polling ... is interesting

Could this be somehow related to control plane policing? You might be hitting some default policy threshold, and may 
have to adjust it to allow snmp from your specific sources at a higher rate.

IIRC on ios-xr that's called lots or sdr (but I had been a while...)

On Fri, Aug 1, 2025, 6:59 AM Drew Weaver via NANOG <nanog () lists nanog org<mailto:nanog () lists nanog org>> wrote:
90 seconds... but also we can poll Supervisor 720s at the same rate and they don't time out or delay responses.

😊


-----Original Message-----
From: Mel Beckman <mel () beckman org<mailto:mel () beckman org>>
Sent: Friday, August 1, 2025 9:37 AM
To: nanog () lists nanog org<mailto:nanog () lists nanog org>
Cc: Drew Weaver <drew.weaver () thenap com<mailto:drew.weaver () thenap com>>; nanog () lists nanog org<mailto:nanog () 
lists nanog org>
Subject: Re: Cisco ASR9902 SNMP polling ... is interesting

How often are you polling the interfaces? SNMP was never meant for high frequency polling (e.g., once per second), yet 
I often see people using SNMP as if it were a SCADA service, which is used in industrial automation for high frequency 
supervisory control and data acquisition. SNMP probes are typically anticipated by device designers to occur at 30 
second or 60 second intervals.

 -mel

> On Aug 1, 2025, at 6:10 AM, Drew Weaver via NANOG <nanog () lists nanog org<mailto:nanog () lists nanog org>> wrote:
>
> Hello,
>
> We purchased an ASR9902 I think almost 2 years ago now intending to replace 4 routers with them.
>
> We had a history of lets just say design decision quirks with the router that prevented us from deploying it until 
> recently.
>
> Then when we finally were able to implement it we've noticed something strange about how SNMP polling works in the 
> router.
>
> If we poll SNMP on any interface that isn't one of the built in management ethernet interfaces the response takes 
> 8x-16x longer to respond and exactly 62% of the polls time out.
>
> If we poll SNMP on the built-in MGMT interfaces the responses are still slower than the ASR9001s that we used to use 
> but they don't seem to time out.
>
> I've had a TAC case with Cisco open over this for weeks now and they are now saying that the slow responses and the 
> 62% poll timeouts are intentional and that they don't see any problem with the design.
>
> I understand the security implications of having control plane stuff responding on all interfaces but the part I 
> don't understand is why bind the SNMP daemon to the non MGMT* interfaces at all if they are making a moral or ethical 
> decision to not allow SNMP to work on non MGMT interfaces. Shouldn't it just not work at all then? Who came up with 
> 62% timeout as the right number?
>
> The larger implication is that I still can't find another router from another vendor that does this.
>
> Has anyone else run into this or did you guys all avoid the ASR 9902 like we should have?
>
> Thanks,
> -Drew
>
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