$5$: When a host knows the IP address of the destination but not its physical address, Which protocol is used to find the physical address? In Question $4,$ consider router R$1$ with IP address $20\mathrm{.}15\mathrm{.}10\mathrm{.}17$ and Ethernet physical address $33445566.$ The router R$1$ has received a packet for the destination host H $.$ Let host H have IP address $20\mathrm{.}15.10\mathrm{.}18($it is in the same Subnet as the RI interface towards H$)$ and has the Ethernet physical address AA$66$BB$77.$ How router R$1$ will know the IP address of Host H$?$ and then the physical address of H $?[5]$