Cisco ASR 1000 Configuration Guide

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Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide
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Chapter 13 Configuring the POS SPAs
Configuration Tasks
• The Frame Relay Local Management Interface (LMI) protocol requires that all permanent virtual
circuit (PVC) status reports fit into a single packet. Using the default MTU of 4470 bytes, this limits
the number 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:
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).
Command Purpose
Router(config-if)# mtu bytes Configures the maximum packet size for an interface,
where:
• bytes—Specifies the maximum number of bytes for
a packet. The default is 4470 bytes.

Cisco ASR 1000 Specifications

General

Brand	Cisco
Model	ASR 1000
Category	Network Router
Language	English