DELL S50V User Manual

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IPv4 Addressing
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Beginning with version 8.3.1.0, when a Gratuitous ARP is received, FTOS installs an ARP entry on all 3 
CPUs.
ARP Learning via ARP Request
In FTOS versions prior to 8.3.1.0, FTOS learns via ARP Requests only if the Target IP specified in the 
packet matches the IP address of the receiving router interface. This is the case when a host is attempting to 
resolve the gateway address.
If the Target IP does not match the incoming interface, then the packet is dropped. If there is an existing 
entry for the requesting host, it is updated.
Figure 21-8.  Learning via Gratuitous ARP
Beginning with FTOS version 8.3.1.0, when ARP Learning via Gratuitous ARP is enabled, the system 
installs a new ARP entry, or updates an existing entry for all received ARP requests.
Figure 21-9.  Learning via Gratuitous ARP
Whether ARP Learning via Gratuitous ARP is is enabled or disabled, the system does not look up the 
Target IP. It only updates the ARP entry for the Layer 3 interface with the source IP of the request.
Task
Command Syntax
Command Mode
Enable ARP learning via gratuitous ARP.
arp learn-enable
CONFIGURATION
Host 1
IP: 1.1.1.2
MAC: AA
Host 2
IP: 1.1.1.3
MAC: BB
ARP Request
Target IP: 1.1.1.3
Target IP is not the VLAN interface
IP. Update existing Host 1 entry.
Drop packet.
VLAN ID: 1.1.1.1
X
Host 1
IP: 1.1.1.2
MAC: AA
Host 2
IP: 1.1.1.3
MAC: BB
ARP Request
Target IP: 1.1.1.3
Target IP is not the VLAN interface
IP. Install new entry for Host 1, or 
update existing Host 1 entry. 
Drop packet.
VLAN ID: 1.1.1.1
ARP Learning via Gratuitous ARP enabled
X