The following commands configure UDP flooding on Router A. Because this configuration does not specify a lower path cost than the default and because the configuration of Router B specifies a lower cost than the default with regard to UDP flooding, Router A acts as a backup to Router B. Because this configuration specifies an IRDP preference of 100 and because Router B specifies a IRDP preference of 90 (ip irdp preference 90), Router A forwards unicast traffic from the trader networks, and Router B is the backup for unicast traffic forwarding.
!Router A: ip forward-protocol spanning-tree ip forward-protocol udp 111 ip forward-protocol udp 3001 ip forward-protocol udp 3002 ip forward-protocol udp 3003 ip forward-protocol udp 3004 ip forward-protocol udp 3005 ip forward-protocol udp 3006 ip forward-protocol udp 5020 ip forward-protocol udp 5021 ip forward-protocol udp 5030 ip forward-protocol udp 5002 ip forward-protocol udp 1027 ip forward-protocol udp 657 ! interface ethernet 0 ip address 200.200.200.61 255.255.255.0 ip broadcast-address 200.200.200.255 no mop enabled ! interface ethernet 1 ip address 164.53.7.61 255.255.255.192 ip broadcast-address 164.53.7.63 ip irdp ip irdp maxadvertinterval 60 ip irdp minadvertinterval 45 ip irdp holdtime 60 ip irdp preference 100 bridge-group 1 bridge-group 1 input-type-list 201 no mop enabled ! interface ethernet 2 ip address 164.53.8.61 255.255.255.192 ip broadcast-address 164.53.8.63 ip irdp ip irdp maxadvertinterval 60 ip irdp minadvertinterval 45 ip irdp holdtime 60 ip irdp preference 100 bridge-group 1 bridge-group 1 input-type-list 201 no mop enabled ! interface ethernet 3 ip address 164.53.9.61 255.255.255.192 ip broadcast-address 164.53.9.63 ip irdp ip irdp maxadvertinterval 60 ip irdp minadvertinterval 45 ip irdp holdtime 60 ip irdp preference 100 bridge-group 1 bridge-group 1 input-type-list 201 no mop enabled ! interface ethernet 4 ip address 164.53.10.61 255.255.255.192 ip broadcast-address 164.53.10.63 ip irdp ip irdp maxadvertinterval 60 ip irdp minadvertinterval 45 ip irdp holdtime 60 ip irdp preference 100 bridge-group 1 bridge-group 1 input-type-list 201 no mop enabled ! router igrp 1 network 164.53.0.0 ! ip name-server 255.255.255.255 snmp-server community public RW snmp-server host 164.53.7.15 public bridge 1 protocol dec bridge 1 priority 255 access-list 201 deny 0xFFFF 0x0000
The following commands configure UDP flooding on Router B. Because this configuration specifies a lower path cost than the default (bridge-group 1 path-cost 50) and because the configuration of Router A accepts the default, Router B forwards UDP packets. Because this configuration specifies an IRDP preference of 90 (ip irdp preference 90) and because Router A specifies a IRDP preference of 100, Router B acts as the backup for Router A for forwarding unicast traffic from the trader networks.
!Router B ip forward-protocol spanning-tree ip forward-protocol udp 111 ip forward-protocol udp 3001 ip forward-protocol udp 3002 ip forward-protocol udp 3003 ip forward-protocol udp 3004 ip forward-protocol udp 3005 ip forward-protocol udp 3006 ip forward-protocol udp 5020 ip forward-protocol udp 5021 ip forward-protocol udp 5030 ip forward-protocol udp 5002 ip forward-protocol udp 1027 ip forward-protocol udp 657 ! interface ethernet 0 ip address 200.200.200.62 255.255.255.0 ip broadcast-address 200.200.200.255 no mop enabled ! interface ethernet 1 ip address 164.53.7.62 255.255.255.192 ip broadcast-address 164.53.7.63 ip irdp ip irdp maxadvertinterval 60 ip irdp minadvertinterval 45 ip irdp holdtime 60 ip irdp preference 90 bridge-group 1 bridge-group 1 path-cost 50 bridge-group 1 input-type-list 201 no mop enabled ! interface ethernet 2 ip address 164.53.8.62 255.255.255.192 ip broadcast-address 164.53.8.63 ip irdp ip irdp maxadvertinterval 60 ip irdp minadvertinterval 45 ip irdp holdtime 60 ip irdp preference 90 bridge-group 1 bridge-group 1 path-cost 50 bridge-group 1 input-type-list 201 no mop enabled ! interface ethernet 3 ip address 164.53.9.62 255.255.255.192 ip broadcast-address 164.53.9.63 ip irdp ip irdp maxadvertinterval 60 ip irdp minadvertinterval 45 ip irdp holdtime 60 ip irdp preference 90 bridge-group 1 bridge-group 1 path-cost 50 bridge-group 1 input-type-list 201 no mop enabled ! interface ethernet 4 ip address 164.53.10.62 255.255.255.192 ip broadcast-address 164.53.10.63 ip irdp ip irdp maxadvertinterval 60 ip irdp minadvertinterval 45 ip irdp holdtime 60 ip irdp preference 90 bridge-group 1 bridge-group 1 path-cost 50 bridge-group 1 input-type-list 201 no mop enabled ! router igrp 1 network 164.53.0.0 ! ip name-server 255.255.255.255 snmp-server community public RW snmp-server host 164.53.7.15 public bridge 1 protocol dec bridge 1 priority 255 access-list 201 deny 0xFFFF 0x0000
Although IP helper addressing is useful in networks that do not require redundancy, when configured in networks that feature redundancy, IP helper addressing results in packet duplication that severely reduces router and network performance.
By configuring UDP flooding, one router forwards UDP traffic without burdening the second router with duplicate packets. By dedicating one router to the task of forwarding UDP traffic, the second router becomes available for forwarding unicast traffic. At the same time, because each router is configured as the backup for the other router, redundancy is maintained; if either router fails, the other router can assume the work of the failed router without intervention from an operator. When compared with IP helper addressing, UDP flooding makes the most efficient use of router resources.