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:
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 220.127.116.11
I’ve seen a few suspended ports in etherchannels lately. Not everyone is familiar with this port status. So let’s take a minute to talk about this:
There is one important rule when configuring etherchannels: All interfaces in the etherchannel need the same speed and duplex settings, trunking encapsulation (dot1q/isl) or the same access VLAN in case of an access port, same STP cost and last but not least: no etherchannel port can be configured in a monitor session (SPAN port).
I’ve passed the R&S Written exam last week!
So, study phase 1 is done. It’s time to start studying for the LAB exam.
Please expect a bit more blogging in the upcoming months, I will share my study experiences 🙂
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.
This is just a summary about the bridging and IRB functions in Cisco routers and switches. The configuration on routers and switches is identical, but only the interfaces are different (real interfaces on routers, vlan interfaces on switches).
If you have a network and a router splits this network, you’ll need the bridging functionality.