Default MTU Values

Table 1 shows the default MTU values which are dependent upon the (sub-) port type, mode, and encapsulation.

Table 1. MTU Default Values

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

Note:
  1. 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.