Chapter 41 ARP Setup
GS2210 Series User’s Guide
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ARP r equest t o t he Sw it ch and t hen sends an I CMP r equest aft er get t ing t he ARP r eply fr om t he
Swit ch. The Swit ch finds no m at ched ent r y for host B in t he ARP t able and br oadcast s t he ARP
r equest t o all t he devices on t he LAN. When t he Sw it ch r eceives t he ARP r eply fr om host B, it
updat es it s ARP t able and also for war ds host A’s I CMP r equest t o host B. Aft er t he Sw it ch get s t he
I CMP r eply from host B, it sends out an ARP r equest t o get host A’s MAC addr ess and updat es t he
ARP t able wit h host A’s ARP r eply. The Sw it ch t hen can for war d host B’s I CMP r eply t o host A.
Gratuitous-ARP
A grat uit ous ARP is an ARP request in w hich bot h t he sour ce and dest inat ion I P addr ess fields ar e
set t o t he I P addr ess of t he device t hat sends t his r equest and t he dest inat ion MAC addr ess field is
set t o t he br oadcast address. Ther e w ill be no r eply t o a grat uit ous ARP r equest .
A device m ay send a grat uit ous ARP packet t o det ect I P collisions. I f a device r est ar t s or it s MAC
addr ess is changed, it can also use grat uit ous ARP t o infor m ot her devices in t he sam e net w or k t o
updat e t heir ARP t able w it h t he new m apping infor m at ion.
I n Grat uit ous- ARP lear ning m ode, t he Swit ch updat es it s ARP t able w it h eit her an ARP r eply or a
grat uit ous ARP r equest .
ARP-Request
When t he Sw it ch is in ARP- Request lear ning m ode, it updat es t he ARP t able w it h bot h ARP r eplies,
grat uit ous ARP r equest s and ARP r equest s.
A
B
ARP Re qu e st
ARP Re ply
I CM P Re qu e st
ARP Re qu e st
ARP Re ply
I CM P Re qu e st
I CM P Re ply
ARP Re qu e st
ARP Re ply
I CM P Re ply
