Arp Learning Via Arp Request - Dell Force10 S4810P Configuration Manual

1. At time t=0 FTOS sends an ARP request for IP A.B.C.D
2. At time t=1 FTOS receives an ARP request for IP A.B.C.D
3. At time t=2 FTOS installs an ARP entry for A.B.C.D only on RP2.
Beginning with version 8.3.1.0, when a Gratuitous ARP is received, FTOS installs an ARP entry on all 3
CPUs.
Task
Enable ARP learning via gratuitous ARP.

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.
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.
Whether ARP Learning via Gratuitous ARP 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.
528
| IPv4 Routing
VLAN ID: 1.1.1.1
ARP Request
Target IP: 1.1.1.3
Host 1
IP: 1.1.1.2
MAC: AA
VLAN ID: 1.1.1.1
ARP Learning via Gratuitous ARP enabled
ARP Request
Target IP: 1.1.1.3
Host 1
IP: 1.1.1.2
MAC: AA
Command Syntax
arp learn-enable
X
Target IP is not the VLAN interface
IP. Update existing Host 1 entry.
Drop packet.
X
Target IP is not the VLAN interface
IP. Install new entry for Host 1, or
update existing Host 1 entry.
Drop packet.
Command Mode
CONFIGURATION
Host 2
IP: 1.1.1.3
MAC: BB
Host 2
IP: 1.1.1.3
MAC: BB