ZyXEL Communications GS2210-8 User Manual page 350

ARP request t o t he Swit ch and t hen sends an I CMP request aft er get t ing t he ARP reply from t he
Swit ch. The Swit ch finds no m at ched ent ry for host B in t he ARP t able and broadcast s t he ARP
request t o all t he devices on t he LAN. When t he Swit ch receives t he ARP reply from host B, it
updat es it s ARP t able and also forwards host A's I CMP request t o host B. Aft er t he Swit ch get s t he
I CMP reply from host B, it sends out an ARP request t o get host A's MAC address and updat es t he
ARP t able wit h host A's ARP reply. The Swit ch t hen can forward host B's I CMP reply t o host A.
A
ARP Re que st
ARP Re ply
I CM P Re qu e st
ARP Re que st
ARP Re ply
I CM P Re ply
Gratuitous-ARP
A grat uit ous ARP is an ARP request in which bot h t he source and dest inat ion I P address fields are
set t o t he I P address of t he device t hat sends t his request and t he dest inat ion MAC address field is
set t o t he broadcast address. There will be no reply t o a grat uit ous ARP request .
A device m ay send a grat uit ous ARP packet t o det ect I P collisions. I f a device rest art s or it s MAC
address is changed, it can also use grat uit ous ARP t o inform ot her devices in t he sam e net work t o
updat e t heir ARP t able wit h t he new m apping inform at ion.
I n Grat uit ous-ARP learning m ode, t he Swit ch updat es it s ARP t able wit h eit her an ARP reply or a
grat uit ous ARP request .
ARP-Request
When t he Swit ch is in ARP- Request learning m ode, it updat es t he ARP t able wit h bot h ARP replies,
grat uit ous ARP request s and ARP request s.
Chapter 41 ARP Setup
ARP Re que st
ARP Re ply
I CM P Re que st
I CM P Re ply
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