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Cisco MDS 9000 Family Troubleshooting Guide
OL-5183-02, Cisco MDS SAN-OS Release 1.3
Chapter 5 Troubleshooting IP Storage Issues
Fine Tuning/Troubleshooting IPS iSCSI TCP Performance
If you do not have access to the host, one way to see if the host is also configured for high MTU/MSS
(as well as the path in the middle) is to check the split packets field in the show ips stats tcp display :
However this is a generic display for all TCP sessions. That is, if you have some Hosts with high
MTU-capable NICs, and some others without, it may be difficult to assess which is which.
MDS_Top# show ips stats tcp interface gig 2/1 detail (truncated output)
TCP Statistics for port GigabitEthernet2/1
TCP send stats
10 segments, 240 bytes
5 data, 5 ack only packets
0 control (SYN/FIN/RST), 0 probes, 0 window updates
0 segments retransmitted, 0 bytes
0 retransmitted while on ethernet send queue, 0 packets split
………
TCP Active Connections
Local Address Remote Address State Send-Q Recv-Q
10.48.69.250:3260 10.48.69.233:1026 ESTABLISH 0 0
10.48.69.250:3260 10.48.69.233:1040 ESTABLISH 0 0
0.0.0.0:3260 0.0.0.0:0 LISTEN 0 0
MDS_Top#
Afterward, traffic starts flowing from the FC storage towards the server that is connected via iSCSI to
the IPS.
MDS_Top# show ips stats tcp interface gig 2/1 detail (truncated output)
TCP Statistics for port GigabitEthernet2/1
TCP send stats
715535 segments, 943511612 bytes
712704 data, 2831 ack only packets
0 control (SYN/FIN/RST), 0 probes, 0 window updates
0 segments retransmitted, 0 bytes
0 retransmitted while on ethernet send queue, 345477 packets split
………
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