of data-link connection identifiers (DLCIs) to 890. The following formula demonstrates how to determine
the maximum DLCIs for a configured interface MTU:
◦ Maximum DLCIs = (MTU bytes – 20)/(5 bytes per DLCI)
◦ Maximum DLCIs for the default MTU = (4470 – 20)/5 = 890 DLCIs per interface
Interface MTU Configuration Task
To modify the MTU size on an interface, use the following command in interface configuration mode:
PurposeCommand
Configures the maximum packet size for an interface,
where:
•
bytes— Specifies the maximum number of bytes
for a packet. The default is 4470 bytes.
Router(config-if)# mtu bytes
To return to the default MTU size, use the no form of the command.
Verifying the MTU Size
To verify the MTU size for an interface, use the show interfaces pos privileged EXEC command and observe
the value shown in the “MTU” field.
The following example shows an MTU size of 4470 bytes for interface port 0 (the first port) on the SPA
installed in subslot 1 of the SIP that is located in slot 2 of the Cisco ASR 1000 Series Routers:
Router# show interfaces pos 2/1/0
POS2/1/0 is up, line protocol is up
Hardware is Packet over Sonet
Internet address is 10.1.1.1/24
MTU 4470 bytes
, BW 155000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255.
Modifying the POS Framing
POS framing can be specified as SONET (Synchronous Optical Network) or SDH (Synchronous Digital
Hierarchy). SONET and SDH are a set of related standards for synchronous data transmission over fiber-
optic networks. SONET is the United States version of the standard published by the American National
Standards Institute (ANSI). SDH is the international version of the standard published by the International
Telecommunications Union (ITU).
To modify the POS framing, use the following command in interface configuration mode:
Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide, Cisco IOS XE
Everest 16.5
OL-14127-17 197
Configuring the POS SPAs
Modifying the POS Framing
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