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MTU Size, Port Channels

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MTU Size The Aggregator auto-configures interfaces to use a maximum MTU size of 12,000 bytes. If a packet includes a Layer 2 header, the difference in bytes between the link MTU and IP MTU must be enough to include the Layer 2 header. For example, for VLAN packets, if the IP MTU is 1400, the link MTU must be no less than 1422: 1400-byte IP MTU + 22-byte VLAN Tag = 1422-byte link MTU The MTU range is 592-12000, with a default of 1554. Table 10-3 lists the various Layer 2 overheads found in FTOS and the number of bytes. Table 10-3. Difference between Link MTU and IP MTU Layer 2 Overhead Ethernet (untagged) VLAN Tag Untagged Packet with VLAN-Stack Header Tagged Packet with VLAN-Stack Header Difference between Link MTU and IP MTU 18 bytes 22 bytes 22 bytes 26 bytes Link MTU and IP MTU considerations for port channels and VLANs are as follows. Port Channels: • All members must have the same link MTU value and the same IP MTU value. • The port channel link MTU and IP MTU must be less than or equal to the link MTU and IP MTU values configured on the channel members. For example, if the members have a link MTU of 2100 and an IP MTU 2000, the port channel's MTU values cannot be higher than 2100 for link MTU or 2000 bytes for IP MTU. VLANs: • All members of a VLAN must have the same IP MTU value. • Members can have different link MTU values. Tagged members must have a link MTU 4 bytes higher than untagged members to account for the packet tag. • The VLAN link MTU and IP MTU must be less than or equal to the link MTU and IP MTU values configured on the VLAN members. For example, the VLAN contains tagged members with a link MTU of 1522 and an IP MTU of 1500 and untagged members with a link MTU of 1518 and an IP MTU of 1500. The VLAN's Link MTU cannot be higher than 1518 bytes and its IP MTU cannot be higher than 1500 bytes. Interfaces | 141

Section	Page
About this Guide	15
Objectives	15
Audience	15
Conventions	16
Information Symbols	16
Related Documents	16
Before You Start	17
Default Settings	17
Other Auto-Configured Settings	18
DCB Support	19
FCoE Connectivity and FIP Snooping	19
iSCSI Operation	19
Link Aggregation	20
Link Tracking	20
VLANs	20
Uplink LAG	20
Server-Facing LAGs	20
Stacking Mode	21
Where to Go From Here	21
Configuration Fundamentals	23
Accessing the Command Line	23
CLI Modes	24
Navigating CLI Modes	25
do Command	26
Undoing Commands	26
Obtaining Help	27
Entering and Editing Commands	28
Command History	29
Filtering show Command Outputs	29
Multiple Users in Configuration Mode	31
Getting Started	33
Front Panel	34
Port Numbering	34
Server-Facing Ports	34
Uplink Ports	35
Stacking Ports	35
Port Configuration	35
Console access	36
Serial Console	36
External Serial Port with a USB Connector	37
Boot Process	37
Configure a Host Name	42
Access the System Remotely	42
Access the Aggregator Remotely	43
Configure the Management Port IP Address	43
Configure a Management Route	44
Configure a Username and Password	44
Configure the Enable Password	44
Configuration File Management	45
Copy Files to and from the System	45
Important Points to Remember	46
Save the Running-Configuration	47
View Files	48
View Configuration Files	49
File System Management	50
View the Command History	51
Upgrading and Downgrading FTOS	51
Aggregator Management	53
Logging	53
Log Messages in the Internal Buffer	53
Disabling System Logging	54
Send System Messages to a Syslog Server	54
Using a Unix System as a Syslog Server	54
Changing System Logging Settings	55
Displaying the Logging Buffer and Logging Configuration	56
Configuring a UNIX Logging Facility Level	57
Enabling Time Stamps on Syslog Messages	58
File Transfer Services	58
Configuration Task List for File Transfer Services	58
Enabling the FTP Server	59
Configuring the FTP Server Parameters	59
Terminal Lines	60
Telnet to Another Network Device	60
Recovering from a Forgotten Password	61
Recovering from a Forgotten Enable Password	61
Recovering from a Failed Start	62
Data Center Bridging (DCB)	65
Ethernet Enhancements in Data Center Bridging	65
Priority-Based Flow Control	66
Enhanced Transmission Selection	67
Data Center Bridging Exchange Protocol (DCBX)	69
Data Center Bridging in a Traffic Flow	69
Data Center Bridging: Auto-DCB-Enable Mode	70
When DCB is Disabled (Default)	70
When DCB is Enabled	71
Lossless Traffic Handling	71
Enabling DCB on Next Reload	72
Enabling Auto-DCB-Enable Mode on Next Reload	72
QoS dot1p Traffic Classification and Queue Assignment	73
How Priority-Based Flow Control is Implemented	74
How Enhanced Transmission Selection is Implemented	75
ETS Operation with DCBX	76
Bandwidth Allocation for DCBX CIN	76
DCB Policies in a Switch Stack	77
DCBX Operation	77
DCBX Operation	77
DCBX Port Roles	78
DCB Configuration Exchange	79
Configuration Source Election	80
Propagation of DCB Information	80
Auto-Detection of the DCBX Version	81
DCBX Example	81
DCBX Prerequisites and Restrictions	82
DCBX Error Messages	83
An error in DCBX operation is displayed using the following syslog messages:	83
Debugging DCBX on an Interface	83
Verifying DCB Configuration	84
Example: PFC and ETS Operation	93
Hierarchical Scheduling in ETS Output Policies	95
Dynamic Host Configuration Protocol (DHCP)	97
DHCP Overview	97
DHCP Packet Format and Options	98
Assigning an IP Address Using DHCP	99
DHCP Client	100
Releasing and Renewing DHCP-based IP Addresses	101
Viewing DHCP Statistics and Lease Information	101
Debugging DHCP Client Operation	102
How DHCP Client is Implemented	104
DHCP Client on a Management Interface	105
DHCP Client on a VLAN	106
DHCP Client Operation with Stacking	106
FIP Snooping	107
Fibre Channel over Ethernet	107
Ensuring Robustness in a Converged Ethernet Network	107
FIP Snooping on Ethernet Bridges	109
FIP Snooping in a Switch Stack	111
How FIP Snooping is Implemented	111
FIP Snooping on VLANs	112
FC-MAP Value	112
Bridge-to-FCF Links	112
Impact on other Software Features	112
FIP Snooping Prerequisites	113
FIP Snooping Restrictions	113
Displaying FIP Snooping Information	114
FIP Snooping Example	121
Debugging FIP Snooping	122
Internet Group Management Protocol (IGMP)	123
IGMP Overview	123
IGMP Version 2	123
Joining a Multicast Group	124
Leaving a Multicast Group	124
IGMP Version 3	125
Joining and Filtering Groups and Sources	126
Leaving and Staying in Groups	127
IGMP Snooping	127
How IGMP Snooping is Implemented on an Aggregator	128
Disabling Multicast Flooding	128
Displaying IGMP Information	128
Interfaces	131
Basic Interface Configuration:	131
Advanced Interface Configuration:	131
Interface Auto-Configuration	132
Interface Types	132
Viewing Interface Information	133
Disabling and Re-enabling a Physical Interface	135
Layer 2 Mode	136
Management Interfaces	136
Accessing an Aggregator	136
Configuring a Management Interface	137
Configuring a Static Route for a Management Interface	139
VLAN Membership	140
Default VLAN	140
Port-Based VLANs	141
VLANs and Port Tagging	141
Configuring VLAN Membership	142
Displaying VLAN Membership	143
Adding an Interface to a Tagged VLAN	144
Port Channel Interfaces	145
Port Channel Definition and Standards	146
Port Channel Benefits	146
Port Channel Implementation	146
1GbE and 10GbE Interfaces in Port Channels	147
Uplink Port Channel: VLAN Membership	147
Server-Facing Port Channel: VLAN Membership	147
Displaying Port Channel Information	148
Interface Range	150
Bulk Configuration Examples	150
Create a Single-Range	150
Create a Multiple-Range	151
Exclude a Smaller Port Range	151
Overlap Port Ranges	151
Commas	151
Monitor and Maintain Interfaces	151
Maintenance Using TDR	153
Flow Control Using Ethernet Pause Frames	154
MTU Size	155
Auto-Negotiation on Ethernet Interfaces	156
Setting Speed and Duplex Mode of Ethernet Interfaces	156
Setting Auto-Negotiation Options	157
Viewing Interface Information	159
Displaying Non-Default Configurations	159
Clearing Interface Counters	161
iSCSI Optimization	163
iSCSI Optimization Overview	163
Monitoring iSCSI Traffic Flows	164
Information Monitored in iSCSI Traffic Flows	164
Detection and Autoconfiguration for Dell EqualLogic Arrays	165
Detection and Port Configuration for Dell Compellent Arrays	165
iSCSI Optimization: Operation	166
Default iSCSI Optimization Values	166
Displaying iSCSI Optimization Information	167
Link Aggregation	169
How the LACP is Implemented on an Aggregator	169
Uplink LAG	169
Server-Facing LAGs	170
LACP Modes	170
Auto-Configured LACP Timeout	170
LACP Example	171
Verifying LACP Operation and LAG Configuration	172
Layer 2	177
Managing the MAC Address Table	177
Clearing MAC Address Entries	177
Displaying the MAC Address Table	178
Network Interface Controller (NIC) Teaming	178
MAC Address Station Move	179
MAC Move Optimization	179
Link Layer Discovery Protocol (LLDP)	181
Overview	181
Protocol Data Units	181
Optional TLVs	182
Management TLVs	182
Organizationally Specific TLVs	183
IEEE Organizationally Specific TLVs	183
TIA-1057 (LLDP-MED) Overview	184
TIA Organizationally Specific TLVs	185
LLDP-MED Capabilities TLV	186
LLDP-MED Network Policies TLV	187
Extended Power via MDI TLV	188
LLDP Operation	189
Viewing the LLDP Configuration	189
Viewing Information Advertised by Adjacent LLDP Agents	190
Clearing LLDP Counters	192
Debugging LLDP	193
Relevant Management Objects	194
Port Monitoring	199
Important Points to Remember	199
Port Monitoring	200
Configuring Port Monitoring	202
Simple Network Management Protocol (SNMP)	205
Implementation Information	205
Configuring the Simple Network Management Protocol	205
Important Point to Remember	205
Setting up SNMP	206
Creating a Community	206
Read Managed Object Values	206
Displaying the Ports in a VLAN Using SNMP	208
Fetching Dynamic MAC Entries Using SNMP	209
Deriving Interface Indices	211
Monitor Port-channels	213
Entity MIBS	214
Stacking	217
Overview	217
Stacking Aggregators	217
Stack Management Roles	218
Stack Master Election	219
Failover Roles	219
MAC Addressing	220
Stacking LAG	220
Stacking VLANs	220
Stacking Port Numbers	221
Configuring a Switch Stack	221
Stacking Prerequisites	222
Cabling Stacked Switches	222
Cabling Restrictions	222
Cabling Redundancy	222
Cabling Procedure	223
Accessing the CLI	223
Configuring and Bringing Up a Stack	223
Adding a Stack Unit	224
Resetting a Unit on a Stack	225
Removing an Aggregator from a Stack and Restoring Quad Mode	225
Verifying a Stack Configuration	226
Using LEDs	226
Using Show Commands	226
Troubleshooting a Switch Stack	229
Troubleshooting Commands	229
Failure Scenarios	231
Stack Member Fails	231
Unplugged Stacking Cable	231
Master Switch Fails	232
Stack-Link Flapping Error	232
Master Switch Recovers from Failure	232
Stack Unit in Card-Problem State Due to Incorrect FTOS Version	233
Stack Unit in Card-Problem State Due to Configuration Mismatch	233
Upgrading a Switch Stack	234
Upgrading a Single Stack Unit	235
Broadcast Storm Control	237
Displaying Broadcast-Storm Control Status	237
Disabling Broadcast Storm Control	237
System Time and Date	239
Setting the Time for the Hardware Clock	239
Setting the Time for the Software Clock	240
Synchronizing the Hardware Clock Using the Software Clock	240
Setting the Time Zone	241
Setting Daylight Savings Time	242
Setting Daylight Saving Time Once	242
Setting Recurring Daylight Saving Time	243
Uplink Failure Detection (UFD)	245
Feature Description	245
How Uplink Failure Detection Works	246
UFD and NIC Teaming	247
Important Points to Remember	248
Disabling Uplink Failure Detection	249
Configuring the Defer Timer	249
Displaying Uplink Failure Detection	250
Debugging UFD on an Interface	253
Upgrade Procedures	255
Debugging and Diagnostics	257
Debugging Aggregator Operation	258
All interfaces on the Aggregator are operationally down	258
Symptom: All Aggregator interfaces are down.	258
Resolution: Ensure that port channel 128 is up and that the Aggregator-facing port channel on the top-of-rack switch is correctly configured.	258
Steps to Take:	258
Broadcast, unknown multicast, and DLF packets are switched at a very low rate	259
Symptom: Broadcast, unknown multicast, and DLF packets are switched at a very low rate.	259
Resolution: Disable broadcast storm control globally on the Aggregator.	259
Steps to Take:	259
Flooded packets on all VLANs are received on a server	260
Symptom: All packets flooded on all VLANs on an Aggregator are received on a server, even if the server is configured as a member of only a subset of VLANs. This behavior happens because all Aggregator ports are, by default, members of all (4094) VLANs.	260
Resolution: Configure a port that is connected to the server with restricted VLAN membership.	260
Steps to Take:	260
Auto-configured VLANs do not exist on a stacked Aggregator	261
Symptom: When an Aggregator is configured and used in a stack, traffic does not flow and the VLAN auto-configuration on all ports is lost. This behavior happens because an Aggregator in stacking mode does not support auto-configured VLANs. Only VLANs...	261
Resolution: You must manually configure VLAN membership on each stack-unit port.	261
Steps to Take:	261
Software show Commands	262
Offline Diagnostics	264
Important Points to Remember	264
Running Offline Diagnostics	264
Trace Logs	265
Auto Save on Crash or Rollover	265
Show Hardware Commands	266
Environmental Monitoring	267
Recognize an Over-Temperature Condition	269
Troubleshoot an Over-Temperature Condition	269
Recognize an Under-Voltage Condition	270
Troubleshoot an Under-Voltage Condition	270
Buffer Tuning	271
Deciding to Tune Buffers	273
Buffer Tuning Commands	273
Using a Pre-Defined Buffer Profile	276
Sample Buffer Profile Configuration	277
Troubleshooting Packet Loss	277
Displaying Drop Counters	278
Dataplane Statistics	279
Displaying Stack Port Statistics	281
Displaying Stack Member Counters	281
Application Core Dumps	282
Mini Core Dumps	282
TCP Dumps	284
Standards Compliance	285
IEEE Compliance	285
RFC and I-D Compliance	286
General Internet Protocols	286
General IPv4 Protocols	287
Network Management (continued)	288