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Interface Overruns on Gigabit Interface Connected to a 300mpbs MPLS circuit. What am I missing?

Dusty Slayer
Level 1
Level 1

So, I am somewhat stumped on this problem. We have a Cisco 1921 Router's Gi0/0 interface connected to a Gigabit switch port. On the other side of the router we have a 300mbps MPLS circuit. Our servers are downstream from the Switch and our remote sites access them through the MPLS circuit. During high utilization periods we're getting around 100-150mbps on the MPLS circuit, and the Switch is sending around 250mbps to the router. The interface speed and duplex is set to Auto/Auto and it's negotiated at Full Duplex on Gi0/0 and Gi0/1. I'm not getting any other errors on the interface, but I'm getting these overruns on both the inside and outside interfaces and sites downstream from this router are complaining of performance issues when accessing resources in this site. I've read that the interface overruns are because the Interface is getting more traffic than it can handle, but I would think a Gigabit Interface could easily handle 300mpbs of traffic. I'm not seeing any errors on the switch. I have some QoS in place to try to prioritize critical systems, but this issue seems to be hampering those efforts as well. What steps should I take next to narrow down this problem? Have I missed something obvious? Thanks in advance!

 

Here is the output of the interfaces:

 

Rotuer Name# sh int
Embedded-Service-Engine0/0 is administratively down, line protocol is down
Hardware is Embedded Service Engine, address is 0000.0000.0000 (bia 0000.0000.0000)
MTU 1500 bytes, BW 10000 Kbit/sec, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output never, output hang never
Last clearing of "show interface" counters 15w6d
Input queue: 0/64/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
GigabitEthernet0/0 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is f8c2.88a4.ad60 (bia f8c2.88a4.ad60)
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 4/255, rxload 7/255
Encapsulation ARPA, 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 15w6d
Input queue: 0/75/39053/1278388 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 29654000 bits/sec, 5414 packets/sec
5 minute output rate 18127000 bits/sec, 4771 packets/sec
2844691358 packets input, 1935298155 bytes, 0 no buffer
Received 101946824 broadcasts (0 IP multicasts)
0 runts, 0 giants, 1630 throttles
50587437 input errors, 0 CRC, 0 frame, 50587437 overrun, 0 ignored
0 watchdog, 2169635 multicast, 0 pause input
1356064879 packets output, 1946255087 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
2012905 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
GigabitEthernet0/0.1 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is f8c2.88a4.ad60 (bia f8c2.88a4.ad60)
Description:
Internet address is
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 4/255, rxload 7/255
Encapsulation 802.1Q Virtual LAN, Vlan ID 1.
ARP type: ARPA, ARP Timeout 04:00:00
Keepalive set (10 sec)
Last clearing of "show interface" counters never
GigabitEthernet0/0.2 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is f8c2.88a4.ad60 (bia f8c2.88a4.ad60)
Description:
Internet address is
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 4/255, rxload 7/255
Encapsulation 802.1Q Virtual LAN, Vlan ID 51.
ARP type: ARPA, ARP Timeout 04:00:00
Keepalive set (10 sec)
Last clearing of "show interface" counters never
GigabitEthernet0/0.3 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is f8c2.88a4.ad60 (bia f8c2.88a4.ad60)
Description:
Internet address is
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 4/255, rxload 7/255
Encapsulation 802.1Q Virtual LAN, Vlan ID 42.
ARP type: ARPA, ARP Timeout 04:00:00
Keepalive set (10 sec)
Last clearing of "show interface" counters never
GigabitEthernet0/1 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is f8c2.88a4.ad61 (bia f8c2.88a4.ad61)
Description:
Internet address is
MTU 1500 bytes, BW 300000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 17/255, rxload 8/255
Encapsulation ARPA, 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 15w6d
Input queue: 0/75/0/1719748 (size/max/drops/flushes); Total output drops: 45095739
Queueing strategy: Class-based queueing
Output queue: 0/1000/0 (size/max total/drops)
5 minute input rate 9446000 bits/sec, 3003 packets/sec
5 minute output rate 21108000 bits/sec, 3652 packets/sec
2787065861 packets input, 2888796802 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
104396 input errors, 0 CRC, 0 frame, 104396 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
4250763788 packets output, 412146024 bytes, 0 underruns
0 output errors, 0 collisions, 0 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

 

1 Accepted Solution

Accepted Solutions

Joseph W. Doherty
Hall of Fame
Hall of Fame

"Have I missed something obvious?"

Possibly yes.  Do you know Cisco recommends a 1921 for only 15 Mbps (duplex)?  The platform can do more, much more even, but it's performance, like ISRs before the 4K series is very dependent on traffic mix and router configuration.

The problem is, not that the gig interfaces cannot accept gig traffic, it's the router cannot process continuous intake at that bandwidth.

What might help, would be to run the interfaces, on the 1921, at 100 Mbps, rather than gig.  Yes, you won't obtain your 300 Mbps, but then you may stop much of the overrun errors too.

You might also try increasing the interface input queues, by a lot, and you might try a CBWFQ policy, on the interface with high egress drops, just using class-default FQ.

Doing what I suggest, might not hugely reduce drops, but perceived performance might improve.

View solution in original post

7 Replies 7

Overrun meaning the frame is big than link capability, 

Joseph W. Doherty
Hall of Fame
Hall of Fame

"Have I missed something obvious?"

Possibly yes.  Do you know Cisco recommends a 1921 for only 15 Mbps (duplex)?  The platform can do more, much more even, but it's performance, like ISRs before the 4K series is very dependent on traffic mix and router configuration.

The problem is, not that the gig interfaces cannot accept gig traffic, it's the router cannot process continuous intake at that bandwidth.

What might help, would be to run the interfaces, on the 1921, at 100 Mbps, rather than gig.  Yes, you won't obtain your 300 Mbps, but then you may stop much of the overrun errors too.

You might also try increasing the interface input queues, by a lot, and you might try a CBWFQ policy, on the interface with high egress drops, just using class-default FQ.

Doing what I suggest, might not hugely reduce drops, but perceived performance might improve.

OK. That is definitely food for thought. Most of our sites are running at 5 or 10mbps, but this site has just increased over time. Plus a couple new sites were added at a higher bandwidth (100mpbs). I've been doing some QoS and policing on the remote sites to try not to overrun this router, but it looks like we've unknowingly outgrown it. I'll see what I can do with increasing the queues and policy to bridge the gap until getting a new router. Fortunately this is a sporadic problem that mostly crops up when there is a large group teleconferencing instead of going to a meeting together like we used to do. I can only see it getting worse though and need to get ahead of it. 

 

I'll try your suggestions this weekend when I can make changes and generate a lot of traffic without too many complaints.

Looking at the overnight data when the backups replicate off site (our normal peak usage on this circuit), I can see a correlation with the CPU spiking close to it's max, but still had some headroom. During the time yesterday during the day when traffic was abnormally high, I could see the the CPU was maxed. 

 

I was looking at options for a replacement router and it looks like the ISR 4221 would be the next logical step. It offers 1.2Gbps throughput. We're not encrypting any traffic through this device, and the only services I'm running on it are DHCP, BGP and a few QoS policies. Do you think this would be a good option?

That's a bit hard to say.

Did you know that the 1.2 Gbps you mention, is with the "boost" license, which effectively removes the software imposed performance caps.  However, what that means is, like your 1921, throughput can vary much based on traffic mix and your configuration.  The 1.2 Gbps might be an "up to" or "best case".

For comparison, did you also know the 1921 is documented as having up to 2.77 Gbps throughput?  When Cisco is saying the 4221 can deliver up to 1.2 Gbps, they're unclear under what conditions.

Also, don't forget, these bandwidth rates are an aggregate for the whole router.  I.e. if you have a WAN link of 300 Mbps, you'll want to have a router that's capable of more than 600 Mbps.  Further, you may want even more for additional bandwidth growth.

I would be a bit nervous using a 4221 unless you can try it, before you must own it.

Performance wise, a 3945E looks to be just about the ideal performance, but it's no longer sold as a new router.

Leo Laohoo
Hall of Fame
Hall of Fame

@Dusty Slayer wrote:
GigabitEthernet0/0 is up, line protocol is up
 reliability 255/255, txload 4/255, rxload 7/255
 Full Duplex, 1Gbps, media type is RJ45
 Last clearing of "show interface" counters 15w6d
  50587437 input errors, 0 CRC, 0 frame, 50587437 overrun, 0 ignored

In the last 15/16 weeks, both Gi0/0 & Gi0/1 are getting so much input errors. 

If I drill this down, should I be expecting speed/duplex mismatch error?  

50587437 input errors, 0 CRC, 0 frame, 50587437 overrun, 0 ignored

All the input errors, here, are overrun errors.

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