[c-nsp] Cisco ASR920-24SZ-IM BVI Feature Limitations

[Adrian Minta]

Doesn't the command "hold-queue 240000 out" on physical interface do the 
same thing ?



On 01/16/2016 06:15 PM, James Jun wrote:
>
> +1 also, we have several ASR920-24SZ-IM's and 24SZ-M's out in the field and we're very happy with them.
>
> Aside from LAG limitations (workaround solution was to not use them :-S), the only other issue I've run into is that default port buffer/queue sizes (48KB?) are rather small.  This is a slight annoyance since typical deployment of 920 has at least 2x 10GE feeding the 1GE revenue ports on the box.  As I understand, 920 only has 12MB shared buffer space so that probably explains it, but on default queue sizes, almost every 1GE end-user port (no traffic-shaping on user ports, just full-rate 1G port with 10G uplink) excessively collects output drops on practically most trivial IMIX usage.
>
> For example, a FreeBSD box sitting with 1GE behind ASR920 just doing wget from a download mirror 50ms away records output drops on 920; whereas a 1GE port off of ASR9K or MX80 would not collect output drops for this type of usage.  Sure, it is reasonable to expect an end-user running Speedtest.net or watching Netflix spamming multiple flows to cause output drops, but not on single flow of download.
>
> As a workaround, raising the queue-limit to 512 KB per 1G port dramatically gets rid of output drops for trivial traffic.  You should still see drops for longhaul bursty traffic overwhelming a 1GE interface when stepping down from 10G uplink, but that's pretty much a reasonable congestion at that point, so dropping packet is better.
>
> 512KB seems to be reasonable; 24x1GE * 512KB = 12.2MB, so we don't oversubscribe the global buffer space, and it's roughly ~4ms of output buffer per port.
>
> !
> class-map match-any cos_all
>   match cos  0  1  2  3  4  5  6  7
> policy-map MC_1G_512kb
>   class cos_all
>    bandwidth percent 100
>    queue-limit 512000 bytes
> !
>
>
> James
>

-- 
Best regards,
Adrian Minta