Changing The Router Id - Foundry Networks Switch and Router Installation And Configuration Manual

Foundry Switch and Router Installation and Configuration Guide
Changing the Size of the Maximum Transmission Unit (MTU)
The Maximum Transmission Unit (MTU) is the maximum size an IP packet can be when encapsulated in a Layer
2 packet. If an IP packet is larger than the MTU allowed by the Layer 2 packet, the Layer 3 Switch fragments the
IP packet into multiple parts that will fit into the Layer 2 packets, and sends the parts of the fragmented IP packet
separately, in different Layer 2 packets. The device that receives the multiple fragments of the IP packet
reassembles the fragments into the original packet.
Since the MTU depends on the encapsulation type, and the encapsulation type can be configured on an individual
port basis, the MTU also can be configured on an individual port basis.
The default MTU for Ethernet II packets is 1500 bytes. The default for SNAP packets is 1492 bytes.
To change the MTU for a port, use either of the following methods.
USING THE CLI
To change the MTU for interface 1/5 to 1000, enter the following commands:
BigIron(config)# int e 1/5
BigIron(config-if-5)# ip mtu 1000
Syntax: ip mtu <num>
The <num> parameter specifies the MTU. Ethernet II packets can hold IP packets from 572 – 1500 bytes long.
Ethernet SNAP packets can hold IP packets from 572 – 1492 bytes long. The default MTU for Ethernet II packets
is 1500. The default MTU for SNAP packets is 1492.
USING THE WEB MANAGEMENT INTERFACE
1. Log on to the device using a valid user name and password for read-write access. The System configuration
panel is displayed.
2. Click on the plus sign next to Configure in the tree view to expand the list of configuration options.
3. Click on the plus sign next to IP in the tree view to expand the list of IP option links.
4. Click on the Interface link to display the interface table.
5. Click on the Modify button in the row for the port.
6. Enter an MTU value from 572 – 1492 if the interface is operating with Ethernet SNAP encapsulation. If the
interface is operating with Ethernet II, enter a value from 572 – 1500.
7. Click the Add button to save the change to the device's running-config file.
8. To configure settings for another port, select the port (and slot, if applicable) and go to step 6.
9. Select the Save link at the bottom of the dialog. Select Yes when prompted to save the configuration change
to the startup-config file on the device's flash memory.

Changing the Router ID

In most configurations, a Layer 3 Switch has multiple IP addresses, usually configured on different interfaces. As
a result, a Layer 3 Switch's identity to other devices varies depending on the interface to which the other device is
attached. Some routing protocols, including Open Shortest Path First (OSPF) and Border Gateway Protocol
version 4 (BGP4), identify a Layer 3 Switch by just one of the IP addresses configured on the Layer 3 Switch,
regardless of the interfaces that connect the Layer 3 Switches. This IP address is the router ID.
NOTE: Routing Information Protocol (RIP) does not use the router ID.
NOTE: If you change the router ID, all current BGP4 sessions are cleared.
By default, the router ID on a Foundry Layer 3 Switch is one of the following:
• If the router has loopback interfaces, the default router ID is the IP address configured on the lowest
numbered loopback interface configured on the Layer 3 Switch. For example, if you configure loopback
interfaces 1, 2, and 3 as follows, the default router ID is 9.9.9.9/24:
15 - 26 December 2000