Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 46)

28 Brocade ICX 6650 Layer 3 Routing Configuration Guide
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Configuring IP parameters – Layer 3 Switches
Configuring packet parameters
You can configure the following packet parameters on Layer 3 Switches. These parameters control
how the Layer 3 Switch sends IP packets to other devices on an Ethernet network. The Layer 3
Switch always places IP packets into Ethernet packets to forward them on an Ethernet port.
• Encapsulation type – The format for the Layer 2 packets within which the Layer 3 Switch sends
IP packets.
• Maximum Transmission Unit (MTU) – The maximum length of IP packet that a Layer 2 packet
can contain. IP packets that are longer than the MTU are fragmented and sent in multiple
Layer 2 packets. You can change the MTU globally or an individual ports:
- Global MTU – The default MTU value depends on the encapsulation type on a port and is
1500 bytes for Ethernet II encapsulation and 1492 bytes for SNAP encapsulation.
- Port MTU – A port default MTU depends on the encapsulation type enabled on the port.
Changing the encapsulation type
The Layer 3 Switch encapsulates IP packets into Layer 2 packets, to send the IP packets on the
network. (A Layer 2 packet is also called a MAC layer packet or an Ethernet frame.) The source
address of a Layer 2 packet is the MAC address of the Layer 3 Switch interface sending the packet.
The destination address can be one of the following:
• The MAC address of the IP packet destination. In this case, the destination device is directly
connected to the Layer 3 Switch.
• The MAC address of the next-hop gateway toward the packet destination.
• An Ethernet broadcast address.
The entire IP packet, including the source and destination address and other control information
and the data, is placed in the data portion of the Layer 2 packet. Typically, an Ethernet network
uses one of two different formats of Layer 2 packet:
• Ethernet II
• Ethernet SNAP (also called IEEE 802.3)
The control portions of these packets differ slightly. All IP devices on an Ethernet network must use
the same format. Brocade Layer 3 Switches use Ethernet II by default. You can change the IP
encapsulation to Ethernet SNAP on individual ports if needed.
NOTE
All devices connected to the Layer 3 Switch port must use the same encapsulation type.
To change the IP encapsulation type on interface 5 to Ethernet SNAP, enter the following
commands.
Brocade(config)# interface ethernet 1/1/5
Brocade(config-if-e10000-1/1/5)# ip encapsulation snap
Syntax: ip encapsulation snap | ethernet_ii
Changing the MTU
The Maximum Transmission Unit (MTU) is the maximum length of IP packet that a Layer 2 packet
can contain. IP packets that are longer than the MTU are fragmented and sent in multiple Layer 2
packets. You can change the MTU globally or on individual ports.