topic Re: Overrun Errors on ASA 5550 in Network Security

Overrun Errors on ASA 5550

Peter_T — Mon, 11 Mar 2019 22:34:32 GMT

I have been getting overrun errors on 3 different ASA 5550 HA pairs with traffic rates less than 100Mbps total. I was told by one TAC guy to split the traffic between the two slots so that traffic comes in one and exits the other to maximize throughput because the 5550 was designed to work that way. Another TAC guy told me to enable ethernet flow control to alleviate the overrun errors because the traffic was bursty, but this doesn't seem to address the root cause of the problem to either. TCP traffic is bursty by nature and has it own flow control mechanism. I can't seem to find any detailed info on why traffic needs to be split for 100Mbps when the marketting throughput number is 1.2G. Is this a design flaw or limitation? Is there a way to alleviate overrun errors?

Overrun Errors on ASA 5550

Marcin Latosiewicz — Fri, 24 Feb 2012 13:18:27 GMT

Good place to start:

http://www.cisco.com/en/US/docs/security/asa/quick_start/5500/5500_quick_start.html#wp35995

Shaping/flow contro/other machanisms can normally alleviate some of the overflow issues.

For the rest you need to check what is causing the overflows, netflow/wireshark/syslog analysis is a good place to start.

Additional note, If you don't have it configured, unicast RPF on all interfaces 🙂

HTH,

Re: Overrun Errors on ASA 5550

Peter_T — Fri, 24 Feb 2012 17:30:18 GMT

Thanks so much for the info, Marcin. The quick start doc basically said the same thing as the TAC person: "For maximum throughput, configure the ASA so that traffic is distributed equally between the two buses. Lay out the network so that traffic enters through one bus and exits through the other. " But do you know the reason why that is necessary? Can you please elaborate on how syslog can reveal what is causing the overflow? How does enabling RPF help with alleviating overflow?

-Peter

Re: Overrun Errors on ASA 5550

Patrick0711 — Fri, 24 Feb 2012 17:32:24 GMT

Are you seeing 'no buffer' counters on the interfaces as well? What is the low count for the 1550 byte memory block in the output of 'show blocks'?

The TAC engineer suggested that you split traffic between the different interface modules because they both have their own internal backplane interfaces (Internal-Data0/0 and Internal-Data1/0). However, this will only help if you're actually overrunning the internal interfaces.

Flow control and overrunning an interface are unrelated. Flow control is determined by a client and server's receive buffers/windows, not by intermediary devices. Additionally, flow control only dictates how many much data can be sent without an ACK but doesn't specify the rate at which the data is sent.

My concern is that there are numerous cases where overruns occur and there are plenty of 1550 byte memory blocks available and the interface doesn't show 'no buffer' counters. I can't imagine why an interface would be overrun in this scenario but have never been able to find a conclusive answer from Cisco.

Re: Overrun Errors on ASA 5550

Peter_T — Fri, 24 Feb 2012 17:45:18 GMT

Thanks for your reply, Patrick. The no buffer counter is 0. 1550 block looks normal.

asa00k/pri/act# show interface gig 1/1

Interface GigabitEthernet1/1 "inside", is up, line protocol is up

Hardware is VCS7380 rev01, BW 1000 Mbps, DLY 10 usec

Auto-Duplex(Full-duplex), Auto-Speed(1000 Mbps)

Media-type configured as RJ45 connector

MAC address 0025.4538.83cd, MTU 1500

IP address 10.174.1.253, subnet mask 255.255.255.0

131235122531 packets input, 66053054633431 bytes, 0 no buffer

Received 147575117 broadcasts, 0 runts, 0 giants

34201765 input errors, 0 CRC, 0 frame, 34201765 overrun, 0 ignored, 0 abort

-----------------------------------------------------------------------^^^^^^^^^^^---------------------------------

0 L2 decode drops

214442064068 packets output, 47534402931048 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 late collisions, 0 deferred

0 input reset drops, 0 output reset drops

0 rate limit drops

input queue (blocks free curr/low): hardware (0/0)

output queue (blocks free curr/low): hardware (0/0)

Traffic Statistics for "inside":

131189361555 packets input, 63641462929613 bytes

214411432424 packets output, 43673527445793 bytes

331334100 packets dropped

1 minute input rate 7085 pkts/sec, 3171622 bytes/sec

1 minute output rate 12327 pkts/sec, 1481679 bytes/sec

1 minute drop rate, 1 pkts/sec

5 minute input rate 7797 pkts/sec, 3358887 bytes/sec

5 minute output rate 13731 pkts/sec, 1683791 bytes/sec

5 minute drop rate, 1 pkts/sec

asa00k/pri/act# show blocks

SIZE MAX LOW CNT

0 1450 1386 1447

4 100 99 99

80 400 336 400

256 1612 1497 1612

1550 7296 6013 7037

2048 2100 1577 2100

2560 164 164 164

4096 100 100 100

8192 100 100 100

16384 110 110 110

65536 16 16 16

asa00k/pri/act# show blocks

SIZE MAX LOW CNT

0 1450 1386 1447

4 100 99 99

80 400 336 400

256 1612 1497 1612

1550 7296 6013 7037

2048 2100 1577 2100

2560 164 164 164

4096 100 100 100

8192 100 100 100

16384 110 110 110

65536 16 16 16

Re: Overrun Errors on ASA 5550

Julio Carvajal — Sun, 26 Feb 2012 18:49:34 GMT

Hello,

Is there a way you can hardcode the interface speed and duplex?

Re: Overrun Errors on ASA 5550

Peter_T — Mon, 27 Feb 2012 03:28:38 GMT

Thanks for your reply. Can you please elaborate on how hardcoding the speed and duplex will help in this case? I see no CRC errors and no collisions.

Re: Overrun Errors on ASA 5550

Julio Carvajal — Mon, 27 Feb 2012 21:39:22 GMT

I am going to do something better, I am going to give you a link that I used the first time I learn about it!

http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a008009491c.shtml#speed

Regards,

Do rate all the helpful posts

Re: Overrun Errors on ASA 5550

Peter_T — Tue, 28 Feb 2012 19:24:28 GMT

Thanks so much for the link - lots of useful info. Unfortunately, I did checked speed and duplex and they matched on both sides and also saw no CRC and no collisions so I ruled it out. CPU utilization is also very low so enable RPF probably won't help either. No buffer count is 0 so I am not sure why we are getting overrun errors at very low traffic rates. We saw overrun errors at as low as 5Mbps with 1 min sampling interval. That doesn't tell whether the traffic is highly bursty instantaneously at some point, but how bursty can it be with 5Mbps worth of traffic? And how much burstiness can the ASA tolerate? I have been trying to get a logical explaination for the overrun errors from Cisco TAC for about 2 weeks, but they just danced around the question. I believe there is an inherent design limitation or software bug that causes this. I am afraid that without getting to the root cause, turning flow control just maquerates the problem.

Overrun Errors on ASA 5550

Borman Bravo — Wed, 07 Mar 2012 16:24:51 GMT

Hi, were you able to resolve this issue, I'm having the same problem. Thanks

Re: Overrun Errors on ASA 5550

Peter_T — Wed, 07 Mar 2012 16:51:53 GMT

Hi, I am getting a lot closer, but not quite there yet. It appears that the ASA5550 cannot tolerate highly bursty traffic even for a very short period of time (saw errors for less than 10Mb worth of bursty traffic). Turning on flow control will clear up the input errors, but I am still trying to gather the data to understand the full impact of flow control on the performance. I am very surprised by the fact the input buffers can not handle such a low level of bursty traffic.

Just got off the phone with the TAC engineer, he was very helpful in providing me with the performance test data. It looks like turning on flow control is the only option.

Re: Overrun Errors on ASA 5550

Borman Bravo — Tue, 13 Mar 2012 19:03:39 GMT

Thanks for sharing this information, I tried looking up the commands to

turn on flow control on the ASA but can't find instructions for 8.3, would you mind sharing this as well? I appreciate it.

Re: Overrun Errors on ASA 5550

Peter_T — Tue, 13 Mar 2012 21:20:19 GMT

You need to use 8.2.5 and later or 8.4.3 and later. The "feature" is not supported in 8.3. The commands are:

On the ASA:

GigabitEthernet0/2

flowcontrol send on

On the Ethernet Switch (if you are using Cisco):

int gigabitEthernet 0/2

flowcontrol receive on

Make sure you do it during maintenace hours or when nobody is looking as this will reset all of your connections .

Re: Overrun Errors on ASA 5550

Borman Bravo — Wed, 14 Mar 2012 14:04:11 GMT

Thanks again, I appreciate your help/

Re: Overrun Errors on ASA 5550

Patrick0711 — Wed, 14 Mar 2012 15:09:46 GMT

Maybe someone from Cisco can actually chime in to better explain how 'bursty' traffic can overrun an interface even though there are sufficient 1550byte memory blocks, 0 'no buffer counters' low throughput, and low CPU utilization.

I've seen this same issue many times in the past and have always received the same response about bursty traffic and flow control. Obviously, there's a limiting factor somewhere in the ASA architecture. Why should I need to use flow control and have the switch buffer the data if, supposedly, there is plenty of buffer space and memory blocks on the ASA?

Re: Overrun Errors on ASA 5550

Borman Bravo — Tue, 27 Mar 2012 13:36:07 GMT

Cisco TACS is now recommending finding those hosts that are generating the bursty traffic, nothing to be done on the ASA to deal with this issue, I'd also like to share the Cisco engineer answer on the ASA handling of traffic and buffering:

"I would like to confirm that the input queue on an interface has a capacity that varies. Depending upon the configuration and speed and duplex settings on both sides it can be 13 packets or a maximum of 75 packets. At the same time the output queue could be as little as 2 packets and as much as 40 packets"

If anyone has any other recommendations I would appreciate it/

Re: Overrun Errors on ASA 5550

Peter_T — Tue, 27 Mar 2012 16:17:14 GMT

Thanks for sharing the info. Did they say what to do with those bursty hosts once you find them? I don't have the full context of the reason and logic behind that suggestion, but it doesn't seem to make any sense. I have told TAC repeatedly that traffic on the network will always be bursty. The only time that you may not have bursty traffic is when you are streaming video at constant bit rate. TCP traffic is bursty by nature. Even if you only have UDP traffic on the network, the accumulative effect of multiple hosts transmitting at the same time still makes the traffic bursty.

The queue size is not as important as how fast the ASA can pull the packets out of the queue and forward them. It seems like they can not do that very fast so the queue gets filled up very quickly and overflowed.

Have you had a chance to try turning on flow control? Did it help?

My experience dealing with TAC is that different TAC engineers may give you complete different answers and sometimes contradicting each other. If the answer doesn't make sense, you can ask for an escalation.

Re: Overrun Errors on ASA 5550

Borman Bravo — Tue, 27 Mar 2012 20:13:45 GMT

Hi, I escalated this ticket, waiting for support. I can't turn on flow control, is not supported on the 8.3 version I'm running, will let you know if I find a resolution from Cisco TACS, thanks.

Re: Overrun Errors on ASA 5550

Mr Brightside — Sun, 08 Jul 2012 03:10:35 GMT

Hi guys,

Did you figure this out with the TAC?

I seem to have the same situation with my 5520s and I am wondering if enabling flow control is the only solution to the problem.

Thanks!

Overrun Errors on ASA 5550

Patrick0711 — Fri, 27 Jul 2012 20:00:48 GMT

Bringing this back from the dead...

Interface GigabitEthernet1/0 "inside", is up, line protocol is up

Hardware is VCS7380 rev01, BW 1000 Mbps, DLY 10 usec

Full-Duplex(Full-duplex), 1000 Mbps(1000 Mbps)

Input flow control is unsupported, output flow control is unsupported

Media-type configured as RJ45 connector

MAC address 1cdf.0f66.35da, MTU 1500

IP address x.x.x.x, subnet mask 255.255.255.0

2136842533 packets input, 2505600752697 bytes, 0 no buffer

Received 6118 broadcasts, 0 runts, 0 giants

3519301 input errors, 0 CRC, 0 frame, 3519301 overrun, 0 ignored, 0 abort

0 L2 decode drops

1231746618 packets output, 186031413394 bytes, 0 underruns

0 pause output, 0 resume output

0 output errors, 0 collisions, 0 interface resets

0 late collisions, 0 deferred

0 input reset drops, 0 output reset drops

0 rate limit drops

input queue (blocks free curr/low): hardware (0/0)

output queue (blocks free curr/low): hardware (0/0)

Traffic Statistics for "inside":

2132528034 packets input, 2462177894354 bytes

1231761102 packets output, 163876265191 bytes

69112 packets dropped

1 minute input rate 15279 pkts/sec, 17668962 bytes/sec

1 minute output rate 8978 pkts/sec, 1071206 bytes/sec

1 minute drop rate, 0 pkts/sec

5 minute input rate 17170 pkts/sec, 20191846 bytes/sec

5 minute output rate 9932 pkts/sec, 1170989 bytes/sec

5 minute drop rate, 0 pkts/sec

This platform has an ASA 5510 Security Plus license.

sh blocks

SIZE MAX LOW CNT

0 400 383 400

4 100 99 99

80 400 284 399

256 3148 2928 3148

1550 2285 1807 2025

2048 2100 1422 2100

2560 164 164 164

4096 100 98 100

8192 100 99 100

16384 100 99 100

65536 16 16 16

Interface is being overrun, there are sufficient 1550 byte memory blocks, the 'no buffer' count is 0. Still, after several years, trying to find an explanation that explains this type of overrun. If it were 'bursty' traffic, wouldn't the interface buffer fill before being overrun which would show an incrementing 'no buffer' counter?