overrun issue on cisco 3845

[safyanjamshaid]

overrun error issue on cisco 3845 gigabit interface?any solution

[balaji.bandi · Accepted solution]

Can you post the example output to undertand the issue correctly

also for reference :

https://www.cisco.com/c/en/us/support/docs/routers/10000-series-routers/6343-queue-drops.html

[safyanjamshaid]

my router is directly connected with isp .router is 3845 .suddenly overrun increased and network performing slow .when overrun normal everything work fine 

[balaji.bandi]

When you get chance post relevant configuration and output to look and suggest.

[MHM Cisco World]

try change to LAG this solve the problem of bottle neck 

[safyanjamshaid]

thnx for reply i have router 3845 with two gigabit port 1 is connected with lan and 2nd is connected with wan ..

how i can configer LAG ?

[MHM Cisco World]

issue is with LAN NOT WAN ?

[safyanjamshaid]

on router interface connected with wan ...overrun causing problem

[Georg Pauwen]

Just out of curiosity...how did you resolve this ?

[MHM Cisco World]

max throughput for this ISR router is 256 Mbps even if you connect giga WAN.

this make WAN overrun error.

[Joseph W. Doherty]

"max throughput for this ISR router is 256 Mbps even if you connect giga WAN."

BTW, only for  (Cisco quoted) "All numbers are for IP packets only - no IPX/AT/DEC, etc. - Mbps calculated by pps * 64bytes * 8bits/byte", i.e. throughput (most) probably (much) more as packet size increases.

[Georg Pauwen]

Hello,

since you have already resolved this (how actually, what did you change ?), the reason for overruns is that the interface receives more traffic than it can handle. The only 'real' option is to reduce the amount of traffic received on the interface, or upgrading the router (capacity). Some buffer tuning might help as well. In case the problem reappears, post the output of:

show interfaces x

where 'x' is the interface that has the overruns, as well as the output of:

show buffers

[Joseph W. Doherty]

For starters, the 3845 is CEF rated at 500 Kpps just doing basic forwarding w/o any additional features.  This does not guarantee (sustained) gig performance.

If you truly want to support a gig interface, at (sustained) gig throughput, you really want a "bigger" (i.e. more "powerful") router, like the "high end" of the ISR 4Ks.

To avoid this issue on a 3845, running your gig interface at 100 Mbps, will likely avoid overruns.

If your overruns are due to transient bursting, and they are input queue drops, adjusting your configuration might decrease such drops.  Would need to see interface stats and router configuration.