[c-nsp] ISR G2 Interface RX Performance

[Blake Dunlap]

Overruns on a software platform router are generally the router being too
underpowered for what you're pushing. Jumping up to an E series (you might
can just replace the engine, I forget which of the parts are modular) would
fix this I think in your specific example, or for a little more depending
on what you have on the horizon, the 1001 asr

Another option is lightly shaping out from the switch if you don't want to
upgrade immediately down to a more absorb-able rate for the router
platform. You're probably barely breaking the threshold just due to the
arrival rate, and I've had success solving this in this manner for a client
in the past who didn't want to spend. Just be aware of the jitter this will
introduce as a consequence.


-Blake


On Fri, Jan 25, 2013 at 5:11 PM, Nathanael Law <
Nathanael.Law at aimco.alberta.ca> wrote:

> Hello all,
>
> We're having some issues with a 3925 and real-time UDP traffic bursts.
>  The bursts
> are approximately 1500 packets long and are sent in 5.7 ms for an
> effective rate
> of ~250 kpps (~375 Mbps).  The steady state traffic on this connection is
> < 10kpps.
>
> Physical Topology
> =================
>
> +------+                      +------+
> |      |                      |      |
> | 3750 | gi2/0/2 ------ gi0/0 | 3925 |
> |      |                      |      |
> +------+                      +------+
>
> Packet captures have shown that the 3750 gi2/0/2 interface has no issues
> sending
> the entire burst; however, packet captures on both the receiving host and
> the
> 3925 shows that only about 1/3rd of the packets show up on the gi0/0
> interface.
> The overrun counter increases slightly with each burst.
>
> 3925#show interfaces gi0/0
> GigabitEthernet0/0 is up, line protocol is up
>   Hardware is PQ3_TSEC, address is 70ca.9bb5.7a80 (bia 70ca.9bb5.7a80)
>   Description: Uplink to core switch 2
>   MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
>      reliability 255/255, txload 12/255, rxload 1/255
>   Encapsulation 802.1Q Virtual LAN, Vlan ID  1., loopback not set
>   Keepalive set (10 sec)
>   Full Duplex, 1Gbps, media type is RJ45
>   output flow-control is unsupported, input flow-control is unsupported
>   ARP type: ARPA, ARP Timeout 04:00:00
>   Last input 00:00:00, output 00:00:00, output hang never
>   Last clearing of "show interface" counters never
>   Input queue: 0/75/176/0 (size/max/drops/flushes); Total output drops: 0
>   Queueing strategy: fifo
>   Output queue: 0/40 (size/max)
>   5 minute input rate 5331000 bits/sec, 2511 packets/sec
>   5 minute output rate 48693000 bits/sec, 5037 packets/sec
>      40386885831 packets input, 7413412230506 bytes, 0 no buffer
>      Received 3800689 broadcasts (0 IP multicasts)
>      0 runts, 0 giants, 111 throttles
>      82202 input errors, 0 CRC, 0 frame, 82202 overrun, 0 ignored
>      0 watchdog, 3800681 multicast, 0 pause input
>      80802723127 packets output, 110122764930458 bytes, 0 underruns
>      0 output errors, 0 collisions, 1 interface resets
>      0 unknown protocol drops
>      0 babbles, 0 late collision, 0 deferred
>      0 lost carrier, 0 no carrier, 0 pause output
>      0 output buffer failures, 0 output buffers swapped out
>
> The only other statistic of note seems to be the rx_overflow_err on the
> gi0/0
> interface:
>
> Internal Driver Information:
>  throttled=111, enabled=111, disabled=0
>  rx_coalesce_failed=0, rx_framing_err=0, rx_overflow_err=1726086,
> rx_buffer_err=65
>  rx_no_enp=0, rx_discard=0
>  tx_one_col_err=0, tx_more_col_err=0, tx_no_enp=0, tx_deferred_err=0
>  tx_underrun_err=0, tx_late_collision_err=0, tx_loss_carrier_err=0
>  tx_exc_collision_err=0, tx_buff_err=0, fatal_tx_err=0
>
> From this it seems that the actual gigabit physical interfaces on the 3925
> cannot
> handle even 11% of line rate (2 Mpps for a 1 Gbps connection @ 64 byte
> packets).
> I knew that the processor can't handle that, but I expected the interface
> itself
> to come at least a little closer given that CEF on the 3925 can supposedly
> handle
> 833 kpps without any features turned on.
>
> Does my analysis seem accurate?  If not, any pointers in the right
> direction would
> be appreciated.  If so, what Cisco routing hardware would be minimally
> required to
> support line-rate 1 Gbps input (the 3925 is a WAN router that basically
> passes
> traffic off to one of our MPLS providers)?  Would the interfaces on an
> ASK1k (ESP5)
>  do the job?
>
> We do have a TAC case open for this issue, but they have been unable to
> provide
> documentation on the limitations of the physical interface so far.
>
> Documents that seem related:
>  - https://supportforums.cisco.com/docs/DOC-2613 (doesn't reference
> anything as new
>    as the ISR G2s, but I figured it may still apply)
>
> Thank you,
>
> Nathanael Law
>
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