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
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