OS10 MTU 組態簡介

涵蓋的關鍵主題 

預設 MTU 組態

• 從版本 10.5.4.4 開始，預設 MTU 值為 9216 位元組。先前為 1532 位元組。
• 設定和驗證 MTU 值的命令：
  • default mtu <value>: 為所有不含使用者設定 MTU 的介面設定自訂 MTU 值
  • no default mtu: 將介面重設為系統預設 MTU 值
  • show default mtu: 顯示系統層級的預設 MTU
  • show interface: 顯示特定介面目前的 MTU 

MTU 組態範例

• 如何使用 CLI 命令顯示和修改預設 MTU 的範例
• 虛擬 LAN （VLAN） 和虛擬網路的設定方案，強調所有介面上 MTU 設定一致的重要性，以避免 L2 和 L3 VPN 變動

考量事項與最佳實務

• 確保所有介面的 MTU 設定一致，包括邊界閘道協定 （BGP） 對等方之間的邏輯和物理介面
• 除了 S4200-ON 系列和 S5148-ON 等特定型號平台外，大部分 Dell 電源交換器都不支援重組
• OS10 會選取在 VLAN 或 VLAN 成員上設定的最低 MTU 值作為 VLAN MTU

 MTU

• 升級至 10.5.4.4 後，尚未使用者設定 MTU 的所有 VLAN 和乙太網路介面上的 MTU 預設為 9216

MTU 組態不正確的潛在問題 

丟包

• 如果 MTU 設置得太低，則會丟棄較大的數據包，從而導致顯著的數據丟失和網路性能下降 

網路變動

• 介面之間的 MTU 設定不一致可能會導致 L2 和 L3 VPN 出現抖動，從而破壞網路穩定性和連線能力。 

延遲增加

• 不正確的 MTU 設定會導致碎片增加，從而導致延遲增加和輸送量降低

顯示預設 MTU。

OS10# show default mtu
Default MTU 9216 bytes

無使用者組態的系統預設值

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)#

• 範例 

OS10# default mtu 9216
OS10# no default mtu

表 54.VLAN MTU 組態的使用案例。

組態	乙太網路介面組態	顯示介面輸出
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

• 範例

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

• 範例

OS10# show default mtu
Default MTU 9216 bytes