Do not enable IP routing on Switch 3.Verfy that SW3 learns its gateway from R3 via IRDP
Configure R3 to advertise its own IP address on the link between R3 and SW3 as a gateway via multicast
Set minimum and maximum interval s to 20 seconds
Set preference to 100
Answer
R3
Interface Fast 0/0
Ip address 172.16.30.3 255.255.255.128
Ip irdp
Ip irdp multicast
Ip irdp maxadvertinterval 20
Ip irdp minadvertinterval 20
Ip irdp holdtime 60
Ip irdp preference 100
R3# debug ip icmp
Aug 12 14:48:35.403: ICMP: src=172.16.30.3, dst=224.0.0.1, irdp advertisement sent
Aug 12 14:48:35.403: IRDP: entries=1, size=2, lifetime=60, bytes=36
Aug 12 14:48:35.403: IRDP: address=172.16.30.3 preference=100
Sw3
SW3(config)#ip gdp irdp
Interface Fast 0/20
Ip address 172.16.30.10 255.255.255.128
Ip irdp
Ip irdp multicast
SW3#debug ip icmp
*Mar ۱ ۰۰:۲۷:۳۶٫۳۴۷: ICMP: rdp advert rcvd type 9, code 0, from 172.16.30.3
SW3#sh ip route
Gateway Using Interval Priority Interface
۱۷۲٫۱۶٫۳۰٫۳ IRDP ۲۶ ۱۰۰ FastEthernet0/20
Default gateway is 172.16.30.3