Nortel Networks 2300 manual Configuring and Managing IP Interfaces and Services, MTU Support

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Configuring and Managing IP Interfaces and Services

MTU Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Configuring and Managing IP Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Configuring the System IP Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Configuring and Managing IP Routes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Managing the Management Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Configuring and Managing DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Configuring and Managing Aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Configuring and Managing Time Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Managing the ARP Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Pinging Another Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 Logging In to a Remote Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Tracing a Route . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 IP Interfaces and Services Configuration Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . 152

MTU Support

WLAN 2300 System Software (WSS Software) supports standard maximum transmission units (MTUs) of 1514 bytes for standard Ethernet packets and 1518 bytes for Ethernet packets with an 802.1Q tag. WSS Software does not support changing of the MTU through software configuration, and WSS Software does not do path MTU discovery.

Communication between WSSes is supported over any path MTU, and the Mobility Domain itself can run over the minimum IP path MTU. However, tunnels between two WSS switches require a path MTU of at least 1448 bytes.

This minimum MTU path is required because Nortel devices use IP tunnels to transport user traffic between WSS switches and to transport user traffic and control traffic between switches and AP access ports. Encapsulation of the packets for tunneling adds an additional 44 bytes to the packet headers, so WSS Software does fragment and reassemble the packets if necessary to fit within the supported MTUs. However, WSS Software does not support defragmentation except at the receiving end of an IP tunnel, and only to reassemble fragments created by another Nortel device for tunneling.

If the path MTU between Nortel devices is less than 1448 bytes, a device in the path might further fragment or drop a tunneled packet. If the packet is further fragmented, the receiving WSS will not be able to reassemble the fragments, and the packet is dropped.

Nortel WLAN Security Switch 2300 Series Configuration Guide