Generally, when the ping operation fails, check ARP entries to determine whether Layer 3 forwarding is correct, and check MAC address entries to determine whether Layer 2 forwarding is correct.
The MAC address table stores information about the MAC addresses learned by the switch. When forwarding an Ethernet frame, the switch searches the MAC address table for the outbound interface according to the destination MAC address and VLAN ID in the Ethernet frame.
Ø A MAC address entry contains four fields: MAC Address, VLAN/VSI, Learned-From, and Type.
Ø The preceding MAC address entry indicates that an interface forwards the frame with the MAC address of 0000-0001-0203 and VLAN ID of 2 through GE0/0/7.
1. Format
display mac-address [ dynamic | blackhole | static ]
2. Function
The display mac-address command displays all MAC address entries on the device.
The display mac-address dynamic command displays MAC address entries that are dynamically learned.
The display mac-address blackhole command displays blackhole MAC address entries that are manually configured.
The display mac-address static command displays static MAC address entries that are manually configured.
Check MAC address entries to determine whether the switch exchanges data with the connected device. Then you can determine whether Layer 2 forwarding is correct.
Format and Function
l The display mac-address vlan vlan-id command displays MAC address entries in a VLAN.
l The display mac-address interface-name command displays MAC address entries on an interface.
l You can run the display mac-address mac-address [ vlan-id ] command to check whether a specified MAC address exists.
To determine whether a MAC address entry on a PC or another device is the MAC address entry of the connected switch, interface, or VLANIF interface, run any of the following commands to obtain the MAC address of the switch, interface, or VLANIF interface.
Format and Function
l The display bridge mac-address command displays the MAC address of the device.
l The display interface interface-name command displays the MAC address of a specified interface. In the command output, the value of Hardware address is the MAC address of the interface.
l The display interface vlanif vlan-id command displays the MAC address of a specified VLANIF interface. In the command output, the value of Hardware address is the MAC address of the VLANIF interface.
Interfaces on a switch are Layer 2 interfaces by default. The MAC address of a Layer 2 interface is the same as the MAC address of the switch. You can check the MAC address of a Layer 2 interface to obtain the MAC address of the device.
The network administrator can query ARP entries on the gateway to learn the IP address of the downstream device, MAC address, interface number, and other information. For example, if the IP address of a user device is known, to learn the MAC address of the user device, query the corresponding ARP entry.
Ø An ARP entry contains six fields: IP ADDRESS, MAC ADDRESS, EXPIRE, TYPE, VLAN/CEVLAN, and INTERFACE.
Ø The last ARP entry indicates that an interface forwards the packet with the MAC address of 0000-0001-0203, IP address of 2.2.2.3, and VLAN ID of 2 through GE0/0/7.
1. Format
display arp [ all | dynamic| static ]
2. Function
The display arp and display arp all commands display all ARP entries on the device.
The display arp dynamic command displays ARP entries that are dynamically learned.
The display arp static command displays ARP entries that are manually configured.
Format
l The display arp network net-number [ net-mask | mask-length ] command displays ARP entries on a specified network segment. l The display arp interface interface-name command displays ARP entries on a specified interface.
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