7705 SAR Interfaces
96
Interface Configuration Guide
3HE 11011 AAAC TQZZA Edition: 01
− the service MTU must be less than or equal to the access port (SAP) MTU
• When the allow-fragmentation command is enabled on an SDP, the current
MTU algorithm is overwritten with the configured path MTU. The administrative
MTU and operational MTU both show the specified MTU value. If the path MTU
is not configured or available, the operational MTU is set to 2000 bytes, and the
administrative MTU displays a value of 0. When allow-fragmentation is
disabled, the operational MTU reverts to the previous value.
For more information, refer to the “MTU Settings” section in the 7705 SAR Services
Guide. To configure various MTU points, use the following commands:
• port MTUs are set with the mtu command, under the config>port context,
where the port type can be Ethernet, DSL, GPON, TDM, serial, or SONET/SDH
• service MTUs are set in the appropriate config>service context
• path MTUs are set with the path-mtu command under the config>service>sdp
context
Figure 8 MTU Points on the 7705 SAR
Frame size configuration is supported for an Ethernet port configured as an access
or a network port.
For an Ethernet adapter card that does not support jumbo frames, all frames
received at an ingress network or access port are policed against 1576 bytes (1572
+ 4 bytes of FCS), regardless of the port MTU. Any frames longer than 1576 bytes
are discarded and the “Too Long Frame” and “Error Stats” counters in the port
statistics display are incremented. See Jumbo Frames for more information.
At network egress, Ethernet frames are policed against the configured port MTU. If
the frame exceeds the configured port MTU, the “Interface Out Discards” counter in
the port statistics is incremented.
19688
NP
SAP
NP
SDP
Access Port MTU
SAP MTU
Service MTU
3
Network Port MTU
5
Path MTU
4
1
2
Ingress Line
Card
Network Egress
Line Card
Fabric
Access Network
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