Table 1 shows the default MTU values which are dependent upon the (sub-) port type, mode, and encapsulation.
Port Type |
Mode |
Encap Type |
Default (bytes) |
---|---|---|---|
Ethernet |
access |
null |
1514 |
Ethernet |
access |
dot1q |
1518 |
Fast Ethernet |
network |
— |
1514 |
Other Ethernet |
network |
— |
92121 |
SONET path or TDM channel |
access |
BCP-null |
1518 |
SONET path or TDM channel |
access |
BCP-Dot1q |
1522 |
SONET path or TDM channel |
access |
IPCP |
1502 |
SONET path or TDM channel |
network |
— |
9208 |
SONET path or TDM channel |
access |
frame-relay |
1578 |
SONET path or TDM channel |
access |
atm |
1524 |
The default MTU for Ethernet ports other than Fast Ethernet is actually the lesser of 9212 and any MTU limitations imposed by hardware which is typically 16K.