802.3ah OAM
Page 88 7210 SAS M, T, X, R6, R12, Mxp Interface Configu-
ration Guide
→ The service MTU must be less than or equal to the SDP path MTU.
→ The service MTU must be less than or equal to the access port (SAP) MTU.
Default MTU Values
Table 14 displays the default MTU values which are dependent upon the (sub-) port type, mode,
and encapsulation.
*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.
Notes:
1. The no service-mtu-check command disables service mtu check. Disabling the service
MTU check allows packets to pass to the egress if the packet length is less than or equal
to the MTU configured on the port. The length of the packet sent from a SAP is limited
only by the access port MTU. In case of a pseudowire, the length of the packet is limited
by the network port MTU (including the MPLS encapsulation).
2. In 7210 SAS, length of the SAP tag (or service-delimiting tag, for a packet received over
a pseudowire) is included in the computation of the packet length before comparing it
with the service-MTU configured for the service.
Packet length= Length of IP packet + L2 header + length of SAP tag
For example, if the IP packet received over a dot1q SAP is 1500 and the service-MTU
configured is 1514, the service MTU validation check fails as:
Packet length=1500 (Length of IP packet) +14 (L2 header) +4 (length of SAP tag) =1518.
The packet is dropped as packet length is greater than the service MTU configured.
Note: Please check the 7210 platform release notes for other restrictions with regards to MTU
checking and processing on each of the platforms.
Table 14: MTU Default Values
Port Type Mode Encap Type Default
(bytes)
Ethernet access null 1514
Ethernet access dot1q 1518
Port mode access qinq 1522
Fast Ethernet network — 1514
Other Ethernet network — 9212*
Ethernet hybrid — 9212
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