Category: IP helper

IP helper with ACL on SVI

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Just another short post about IP helpers:
It took me last week a few minutes to figure out why my new configured IP helpers were not working.
The starting config was like:

interface Vlan6
 description Voice VLAN
 ip address 192.168.1.251 255.255.255.0
 ip access-group Voice in
 ip helper-address 192.168.15.1
 ip helper-address 192.168.15.3
 no ip redirects
 no ip unreachables
 standby 6 ip 192.168.1.254
 standby 6 timers 1 2
 standby 6 priority 110
 standby 6 preempt
ip access-list extended Voice
 permit ip host 192.168.1.9 192.168.254.0 0.0.0.255
 permit ip host 192.168.1.2 192.168.254.0 0.0.0.255
 permit ip 192.168.1.0 0.0.0.255 192.168.15.0 0.0.0.255
 permit ip any host 224.0.0.2

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IP helper

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We all are familiar with the IP helper command to allow DHCP requests (broadcast) passthrough a router to get as a unicast packet to a DHCP server. Pretty easy and simple.. But the IP helper can do more!
When there is a network with multiple vlans and you need the use the good old “net send” command from Windows computers on all computers on all the VLAN’s, you have to configure the IP helper.
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