Cisco MDS Nexus Switching mode? Cut-through or Store and forwards?

[Jay47110]

Hi,

I have a question regarding the default switching mode on Cisco MDS Nexus DS-C9396S-K9 switch running OS 8.4(2a). Is it cut-through or Store and forwards? 

Also, how can I verify that? Is there a command to show the current mode?

[balaji.bandi]

depends on requirement you can choose :

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus9000/sw/7-x/layer2/configuration/guide/b_Cisco_Nexus_9000_Series_NX-OS_Layer_2_Switching_Configuration_Guide_7x/Configuring_Switching_Modes.html

[Jay47110]

Hi @balaji.bandi Thanks for the response.
The switch in question is an MDS FC switch, "MDS 9396S 96X16G FC". How can I verify which switching mode is configured? I cannot seem to find any command that shows me the switching mode.

The switching-mode commands aren't available.

Kind regards

[Joseph W. Doherty]

Going by @balaji.bandi reference, we find:

Default Settings for Switching Modes

Cut-through switching is enabled by default.

(Which I find surprising, as cut-through adds a bit of risk.)

As to determining what mode is active, it looks like you might need to search the config for:

"no switching-mode store-forward" or "switching-mode store-forward".

[Jay47110]

Thanks @Joseph W. Doherty. 
Yes, I've checked the configuration of the MDS switch for any mentions to switching-mode, but nothing found. Can I conclude that its on cut-through in this case?

Kind regards

[balaji.bandi]

Can you post show version  full out put from device, 

[Jay47110]

Please see below:

Cisco Nexus Operating System (NX-OS) Software
TAC support: http://www.cisco.com/tac
Documents: http://www.cisco.com/en/US/products/ps9372/tsd_products_support_series_home.html
Copyright (c) 2002-2020, Cisco Systems, Inc. All rights reserved.
The copyrights to certain works contained herein are owned by
other third parties and are used and distributed under license.
Some parts of this software are covered under the GNU Public
License. A copy of the license is available at
http://www.gnu.org/licenses/gpl.html.

Software
BIOS: version 5.2.24
loader: version N/A
kickstart: version 8.4(2a)
system: version 8.4(2a)
BIOS compile time: 04/04/2020
kickstart image file is: bootflash:///m9300-s1ek9-kickstart-mz-npe.8.4.2a.bin
kickstart compile time: 7/11/2020 12:00:00 [06/23/2020 11:55:02]
system image file is: bootflash:///m9300-s1ek9-mz-npe.8.4.2a.bin
system compile time: 7/11/2020 12:00:00 [06/23/2020 13:22:05]

Hardware
cisco MDS 9396S 96X16G FC (2 RU) Chassis ("2/4/8/10/16 Gbps FC/Supervisor-4")
Motorola, 476fpe with 3890532 kB of memory.
Processor Board ID JAE21280BPK

Device name: MDS-A
bootflash: 3915776 kB

[balaji.bandi · Accepted solution]

Apologies before i was provided the Nexus switches who want to use FCoE that nexus command reference:

MDS we generally do not change day-to-day operation - for reference as below :

switch# show interface iscsi x/x

Sack is disabled

QOS code point is 0

Forwarding mode: pass-thru

TMF Queueing Mode : disabled

Proxy Initiator Mode : enabled

I quickly looked at my resource here my the details I found to share for you :

https://blogs.cisco.com/datacenter/mds-9000-series-switch-architecture-part-1-superior-crc-error-handling

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/mds9000/sw/4_1/configuration/guides/fm_4_1/fmguide/ciscsi.html

[Jay47110]

Thanks @balaji.bandi 

I have read the blog post by Bhavin Yadav which to me suggests MDS use Cut-through forwarding. Is that correct?

Our MDS switch is used for FC instead of ISCSI. And looking at the interface details, I still cannot see any reference of forwarding mode, see output below:

show interface fc1/4
fc1/4 is trunking
Port description is Uplink
Hardware is Fibre Channel, SFP is short wave laser w/o OFC (SN)
Port WWN is 10:06:01:da:fe:93:68:10
Peer port WWN is 10:5f:61:73:1e:3d:f9:00
Admin port mode is E, trunk mode is on
snmp link state traps are enabled
Port mode is TE
Port vsan is 1
Admin Speed is 8 Gbps
Operating Speed is 8 Gbps
Rate mode is dedicated
Port flow-control is R_RDY

Transmit B2B Credit is 240
Receive B2B Credit is 500
B2B State Change: Admin(on), Oper(down)
Receive data field Size is 2112
Beacon is turned off
Logical type is core
Belongs to port-channel10
Trunk vsans (admin allowed and active) (1,202)
Trunk vsans (up) (1,202)
Trunk vsans (isolated) ()
Trunk vsans (initializing) ()
5 minutes input rate 58820416 bits/sec,7352552 bytes/sec, 5013 frames/sec
5 minutes output rate 196834560 bits/sec,24604320 bytes/sec, 13482 frames/sec
1175841966 frames input,1972837037180 bytes
0 discards,0 errors
0 invalid CRC/FCS,0 unknown class
0 too long,0 too short
3369247934 frames output,6422712186264 bytes
0 discards,0 errors
0 input OLS,0 LRR,0 NOS,0 loop inits
0 output OLS,0 LRR, 0 NOS, 0 loop inits
500 receive B2B credit remaining
240 transmit B2B credit remaining
240 low priority transmit B2B credit remaining
Last clearing of "show interface" counters: 2d05h

[balaji.bandi]

which to me suggests MDS use Cut-through forwarding. Is that correct?

we have been mentioned in each post that is the default.

[Jay47110]

Thanks mate. Appreciate the help.

[Joseph W. Doherty]

Unsure, in light of the follow on posts.

Have you tried searching the output from "show running-config all"?

[MHM Cisco World · Accepted solution]

https://community.cisco.com/t5/data-center-switches/9148t-and-9396t-routing-architecture-store-and-forward-or-cut/td-p/4397856

[MHM Cisco World]

 Bhavin Yadav is cisco employer. so sure he is right.