OS10 MTU 配置简介

涵盖的关键议题 

默认 MTU 配置

• 从版本 10.5.4.4 开始，默认 MTU 值为 9216 字节。以前，它是 1532 字节。
• 用于配置和验证 MTU 值的命令：
  • default mtu <value>: 为没有用户配置 MTU 的所有接口设置自定义 MTU 值
  • no default mtu: 将接口重置为系统默认 MTU 值
  • show default mtu: 显示系统级默认 MTU
  • show interface: 显示特定接口的当前 MTU 

MTU 配置示例

• 如何使用 CLI 命令显示和修改默认 MTU 的示例
• 虚拟 LAN （VLAN） 和虚拟网络的配置方案，重点强调在所有接口上保持一致的 MTU 设置以避免 L2 和 L3 VPN 抖动的重要性

注意事项和最佳实践

• 确保所有接口（包括边界网关协议 （BGP） 对等方之间的逻辑和物理接口）的 MTU 设置一致
• 除 S4200-ON 系列和 S5148-ON 平台等特定型号外，大多数戴尔电源交换机不支持碎片化
• OS10 选择在 VLAN 或 VLAN 成员上配置的最低 MTU 值作为 VLAN MTU

 MTU

• 升级到 10.5.4.4 后，对于尚未配置用户配置 MTU 的所有 VLAN 和以太网接口，MTU 默认为 9216

MTU 配置不正确的潜在问题 

数据包丢失

• 如果 MTU 设置得太低，则会丢弃较大的数据包，从而导致严重的数据丢失和网络性能下降 

网络抖动

• 接口之间的 MTU 设置不一致可能会导致 L2 和 L3 VPN 抖动，从而破坏网络稳定性和连接性 

延迟增加

• 不正确的 MTU 设置可能会导致碎片增加，从而导致更高的延迟和更低的吞吐量

显示默认 MTU。

OS10# show default mtu
Default MTU 9216 bytes

无用户配置的系统默认值

OS10# show interface ethernet 1/1/1
Ethernet 1/1/1 is up, line protocol is down
Hardware is Eth, address is 90:b1:00:00:00:a0
 Current address is 90:b1:00:00:00:a0
Pluggable media present, QSFP+ type is QSFP+ 40GBASE-LR4
 Wavelength is 1311
 Receive power reading is no power
Interface index is 11
Internet address is not set
Mode of IPv4 Address Assignment: not set
Interface IPv6 oper status: Disabled
MTU 9216 bytes, IP MTU 1500 bytes
LineSpeed 0, Auto-Negotiation off
Flowcontrol rx off tx off
ARP type: ARPA, ARP Timeout: 60
Last clearing of "show interface" counters: 20:45:24
Queuing strategy: fifo
Input statistics:
 0 packets, 0 octets
 0 64-byte pkts, 0 over 64-byte pkts, 0 over 127-byte pkts
 0 over 255-byte pkts, 0 over 511-byte pkts, 0 over 1023-byte pkts
 0 Multicasts, 0 Broadcasts, 0 Unicasts
 0 runts, 0 giants, 0 throttles
 0 CRC, 0 overrun, 0 discarded
Output statistics:
 0 packets, 0 octets
 0 64-byte pkts, 0 over 64-byte pkts, 0 over 127-byte pkts
 0 over 255-byte pkts, 0 over 511-byte pkts, 0 over 1023-byte pkts
 0 Multicasts, 0 Broadcasts, 0 Unicasts
 0 throttles, 0 discarded, 0 Collisions, wred drops
Rate Info(interval 30 seconds):
 Input 0 Mbits/sec, 0 packets/sec, 0% of line rate
Output 0 Mbits/sec, 0 packets/sec, 0% of line rate
Time since last interface status change: 20:45:25
OS10# configure terminal
OS10(config)# default mtu 9000
OS10(config)#

• 示例 

OS10# default mtu 9216
OS10# no default mtu

表 54.VLAN MTU 配置的用例。

配置	以太网接口 配置	show interface output
interface vlan300 no shutdown !	interface ethernet1/1/6 no shutdown switchport mode trunk switchport trunk allowed vlan300 ! interface ethernet1/1/9 no shutdown switchport mode trunk switchport trunk allowed vlan300	OS10# show interface vlan300 Vlan300 is up, line protocol is up Address is 14:10:10:0d:00:e9, Current address is 14:10:10:0d:00:e9 Interface index is 84 Internet address is not set Mode of IPv4 Address Assignment: not set Interface IPv6 oper status: Enabled Link local IPv6 address: fe80::1010:10ff:fe0d:e9/10 MTU 1532 bytes, IP MTU 1500 bytes
interface vlan300 no shutdown !	interface ethernet1/1/6 no shutdown switchport mode trunk switchport trunk allowed vlan300 ! interface ethernet1/1/9 no shutdown switchport mode trunk switchport trunk allowed vlan300 mtu 1312	OS10# show interface vlan300 Vlan300 is up, line protocol is up Address is 14:10:10:0d:00:e9, Current address is 14:10:10:0d:00:e9 Interface index is 84 Internet address is not set Mode of IPv4 Address Assignment: not set Interface IPv6 oper status: Enabled Link local IPv6 address: fe80::1010:10ff:fe0d:e9/10 MTU 1312 bytes, IP MTU 1280 bytes
virtual-network 3333 ! interface vlan300 no shutdown virtual-network 3333 !	interface ethernet1/1/6 no shutdown switchport mode trunk switchport trunk allowed vlan300 ! interface ethernet1/1/9 no shutdown switchport mode trunk switchport trunk allowed vlan300 mtu 1312	OS10# # show interface vlan300 Vlan300 is up, line protocol is up Address is 14:18:77:0d:00:e9, Current address is 14:18:77:0d:00:e9 Interface index is 84 Internet address is not set Mode of IPv4 Address Assignment: not set Interface IPv6 oper status: Enabled Link local IPv6 address: fe80::1618:77ff:fe0d:e9/64 MTU 1532 bytes, IP MTU 1500 bytes
virtual-network 3333 ! interface vlan300 no shutdown virtual-network 3333 ! interface virtual-network 3333	interface ethernet1/1/6 no shutdown switchport mode trunk switchport trunk allowed vlan300 ! interface ethernet1/1/9 no shutdown switchport mode trunk switchport trunk allowed vlan300 mtu 1312	show interface vlan300 Vlan300 is up, line protocol is up Address is 14:18:77:0d:00:e9, Current address is 14:18:77:0d:00:e9 Interface index is 84 Internet address is not set Mode of IPv4 Address Assignment: not set Interface IPv6 oper status: Enabled Link local IPv6 address: fe80::1618:77ff:fe0d:e9/64 MTU 1532 bytes, IP MTU 1500 bytes OS10# show interface virtual-network 3333 Virtual-network 3333 is up, line protocol is up Address is 14:18:77:0d:00:ea, Current address is 14:18:77:0d:00:ea Interface index is 87 Internet address is not set Mode of IPv4 Address Assignment: not set Interface IPv6 oper status: Enabled MTU 1312 bytes, IP MTU 1280 bytes

• 示例

OS10(conf-if-eth1/1/7)# mtu 3000

• 示例

OS10# show default mtu
Default MTU 9216 bytes