[c-nsp] overruns on a lightly loaded ethernet port

[Robert Larsen]

Well, I know what results we got on our network, and roughly 2.3Mbps
continuous traffic with 192byte packet size was about the limit for a
2621XM.  The traffic was bi-directional using a RAD TDMoIP at each end.

Rob.

-----Original Message-----
From: Joe Maimon [mailto:jmaimon at ttec.com] 
Sent: 12 May 2005 01:28
To: Robert Larsen
Subject: Re: [c-nsp] overruns on a lightly loaded ethernet port



Robert Larsen wrote:
> We've seen similar problems on FE interfaces on 2621 routers, and this is
> most likely because the burst of traffic is too much for the input buffer
on
> the interface to deal with, so the router has to effectively tail drop
> packets which causes the overruns in the interface stats.
> 
> Although these "low-end" routers (2600 and 3600 series) have FE
interfaces,
> they have fairly limited buffers and processing power, and as such could
> never deal with traffic arriving at anything approaching line rate for any
> length of time.
> 
> We've done some testing on a 2621XM a few years ago, and up to approx.
2Mbps
> with a packet size of 192 bytes (or greater) it just about coped (CPU was
> running at 80-100%), but any increase in traffic rate *or* decrease in
> packet size just maxed the box out completely.
> 
2Mbps??? No way......Even a 1600 does better than that.

Perhaps you mean 2Megabytes.. -> ~20Mbps

> Cheers,
> 
> Rob.
> 
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Burton Windle
> Sent: 11 May 2005 22:38
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] overruns on a lightly loaded ethernet port
> 
> I have a 3640, running 12.2(28), connected directly to a 6509 via 100bT. 
> Every now and then, I see a large burst of 'overruns' reported on the
> 3640's FastEth int; however, this connection is very lightly used 
> (~2megabit/sec average). I am under the impression that overruns on an 
> Ethernet interface happen when one side tries to send too fast, but this
> interface never pushes more than 5 megabit/sec.
> 
> 5-3640-WAN>sh proc cpu
> CPU utilization for five seconds: 17%/16%; one minute: 12%; five minutes:
> 17%
> 
> !
> interface FastEthernet0/0
>   description ***6509_PORT2/1***
>   ip address 192.168.1.4 255.255.255.0
>   ip route-cache flow
>   speed 100
>   full-duplex
> 
> 5-3640-WAN>sh int fastEthernet 0/0
> FastEthernet0/0 is up, line protocol is up
>    Hardware is AmdFE, address is 0006.2889.e301 (bia 0006.2889.e301)
>    Description: ***5-6509-1_PORT2/1***
>    Internet address is 192.168.1.4/24
>    MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
>       reliability 255/255, txload 3/255, rxload 3/255
>    Encapsulation ARPA, loopback not set
>    Keepalive set (10 sec)
>    Full-duplex, 100Mb/s, 100BaseTX/FX
>    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 2d01h
>    Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
>    Queueing strategy: fifo
>    Output queue: 0/40 (size/max)
>    5 minute input rate 1304000 bits/sec, 592 packets/sec
>    5 minute output rate 1476000 bits/sec, 598 packets/sec
>       62322869 packets input, 4032355232 bytes
>       Received 157135 broadcasts, 0 runts, 0 giants, 0 throttles
>       750 input errors, 0 CRC, 0 frame, 750 overrun, 0 ignored
>       0 watchdog
>       0 input packets with dribble condition detected
>       60861002 packets output, 108203385 bytes, 0 underruns
>       0 output errors, 0 collisions, 0 interface resets
>       0 babbles, 0 late collision, 0 deferred
>       0 lost carrier, 0 no carrier
> 
> 
> 
> 5-6509-1> sh port 2/1
> Port  Name                 Status     Vlan       Duplex Speed Type
> ----- -------------------- ---------- ---------- ------ ----- ------------
>   2/1  ***5-3640-WAN***     connected  1          full   100
10/100BaseTX
> 
> Port  AuxiliaryVlan AuxVlan-Status     InlinePowered     PowerAllocated
>                                     Admin Oper   Detected mWatt mA @42V
> ----- ------------- -------------- ----- ------ -------- ----- --------
>   2/1  none          none           off   off    no       0     0
> 
> 
> Port  Security Violation Shutdown-Time Age-Time Max-Addr Trap     IfIndex
> ----- -------- --------- ------------- -------- -------- -------- -------
>   2/1  disabled  shutdown             0        0        1 disabled      59
> 
> Port  Num-Addr Secure-Src-Addr   Age-Left Last-Src-Addr
> Shutdown/Time-Left
> ----- -------- ----------------- -------- -----------------
> ------------------
>   2/1         0                 -        -                 -        - 
> -
> 
> Port     Broadcast-Limit Multicast Unicast Total-Drop
> -------- --------------- --------- ------- --------------------
>   2/1                   -         -       -                    0
> 
> Port  Send FlowControl  Receive FlowControl   RxPause    TxPause
>        admin    oper     admin     oper
> ----- -------- -------- --------- ---------   ---------- ----------
>   2/1  off      off      off       off         0          0
> 
> Port  Status     Channel              Admin Ch
>                   Mode                 Group Id
> ----- ---------- -------------------- ----- -----
>   2/1  connected  off                      4     0
> 
> Port  Align-Err  FCS-Err    Xmit-Err   Rcv-Err    UnderSize
> ----- ---------- ---------- ---------- ---------- ---------
>   2/1           0          0          0          0         0
> 
> Port  Single-Col Multi-Coll Late-Coll  Excess-Col Carri-Sen Runts
Giants
> ----- ---------- ---------- ---------- ---------- --------- ---------
> ---------
>   2/1           0          0          0          0         0         0
> 0
> 
> Port  Last-Time-Cleared
> ----- --------------------------
>   2/1  Fri Apr 1 2005, 22:16:01
> 
> 
> 
> Any idea what would be causing these?
>