FW-4-TCP_OoO_SEG: TCP reassembly queue overflow - session

[marc.groenen]

After upgrading a Cisco 892 to IOS c890-universalk9-mz.151-4.M3.bin from c890-universalk9-mz.124-22.YB.bin(reason was tracebacks) we have noticed the following message's in the logging:

%FW-4-TCP_OoO_SEG: Dropping TCP Segment: seq:1628726886 1492 bytes is out-of-order; expected seq:1628698086. Reason: TCP reassembly queue overflow - session x:42024 to x:80 on zone-pair ccp-zp-in-out class ccp-protocol-http

%FW-4-TCP_OoO_SEG: Deleting session as expected TCP segment with seq:972828144 has not arrived even after 25 seconds - session x:57229 to x:80 on zone-pair ccp-zp-in-out class ccp-protocol-http

After some research we tuned the timers of the tcp reassembly

ip inspect max-incomplete high 8000

ip inspect max-incomplete low 7900

ip inspect one-minute high 8000

ip inspect one-minute low 7900

ip inspect udp idle-time 360

ip inspect dns-timeout 10

ip inspect tcp idle-time 7200

ip inspect tcp finwait-time 10

ip inspect tcp max-incomplete host 1000 block-time 0

ip inspect tcp reassembly queue length 1024

ip inspect tcp reassembly timeout 60

ip inspect tcp reassembly memory limit 256000

However the message's still appear and i cant explain why the sh ip inspect statistics is empty

#sh ip inspect statistics

Interfaces configured for inspection 0

Session creations since subsystem startup or last reset 0

Current session counts (estab/half-open/terminating) [0:0:0]

Maxever session counts (estab/half-open/terminating) [0:0:0]

Last session created never

Last statistic reset never

Last session creation rate 0

Maxever session creation rate 0

Last half-open session total 0

TCP reassembly statistics

  received 0 packets out-of-order; dropped 0

  peak memory usage 0 KB; current usage: 0 KB

  peak queue length 0

The message's did not occur while running c890-universalk9-mz.124-22.YB

[mirober2 · Accepted solution]

Hi Marc,

The 'ip inspect' commands and statistics are used for CBAC rather than zone-based firewall. For ZBF, you can tune the reassembly settings with a parameter-map:

parameter-map type ooo global
     tcp reassembly queue length 

You can view the queue statistics with the 'show policy-firewall stats all' or 'show policy-map type inspect zone-pair' commands.

Ultimately though, you should investigate why the router is receiving so many out-of-order packets and resolve that issue upstream.

-Mike

[marc.groenen]

Thank you for youre reply.

I have also tried the paramet-map ooo settings but these also didnt resolve the issue.

Im not getting any complaints from the clients at the site.

I will go onsite next week and will do some testing/sniffing.

UPDATE:

After tweaking the buffers and time outs the TCP reassembly queu overflow message does not occur anymore.

Now only the following message occurs:

%FW-4-TCP_OoO_SEG: Deleting session as expected TCP segment with seq:4121294117 has not arrived even after 900 seconds - session xxxxx to xxxxxxxxx on zone-pair ccp-zp-in-out class ccp-protocol-http.

During an onsite test the test client also generated this message however the client did not notice this and his download and the speed where OK.

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