IP helper with ACL on SVI

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
 ip access-group Voice in
 ip helper-address
 ip helper-address
 no ip redirects
 no ip unreachables
 standby 6 ip
 standby 6 timers 1 2
 standby 6 priority 110
 standby 6 preempt
ip access-list extended Voice
 permit ip host
 permit ip host
 permit ip
 permit ip any host


Etherchannel – suspended port state

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).


Passed R&S Written

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 🙂

IP helper

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.

Bridging / IRB

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.