Comments on: Forwarding a DHCP Request using Cisco ip helper-address command

By: sashikanth

sashikanth — Tue, 03 May 2011 14:55:01 +0000

Hi Admin,
Excellent Blog for biggners. my question is i don’t have ASA. i have Forefront firewall and cisco 3560 L3 switch. i am able to communicate between the vlans but not to internet through ASA firewall.
how do i communicate to internet through Forefront TMG

By: Aedu

Aedu — Thu, 06 Jan 2011 12:51:47 +0000

> I guess the DHCP-Server does not recognize the relay agent and answers with a broadcast?
Makes no sense. The DHCP-Server must reply by unicast. BUT STILL What makes the Relay Agent forward packages back to the source network?

Aedu

By: Aedu

Aedu — Thu, 06 Jan 2011 12:31:40 +0000

Great article

I guess the DHCP-Server does not recognize the relay agent and answers with a broadcast?
What makes the relay agent forward the answer of the DHCP server (DHCPOFFER, DHCPACK) to its subnet (192.168.1.0/24)? Must the src-ip address in the ip header or the in option 54 (DHCP server identifier) match? or both?

Regards
Aedu

P.s. Please excuse my english. I’m not a native speaker…

By: Felix

Felix — Thu, 14 Oct 2010 15:55:11 +0000

i did create the layer 2 vlan but still no luck….

By: Felix

Felix — Thu, 14 Oct 2010 14:26:17 +0000

Ok, thanks a lot, i d just thought the config below was enough:i will create the vlans now. thanks once again

interface range FastEthernet0/1 – 24
description Link to PC
switchport access vlan 2
switchport mode access
switchport voice vlan 101
spanning-tree portfast

By: Blog Admin

Blog Admin — Thu, 14 Oct 2010 13:37:16 +0000

It means you have not created the Layer 2 vlans on each switch as I told you before.

See the following post:

http://www.networkstraining.com/how-to-configure-vlans-on-a-cisco-switch/

By: Felix

Felix — Thu, 14 Oct 2010 12:54:34 +0000

any assistance please? i am sorry for being such a nuisance

By: Felix

Felix — Thu, 14 Oct 2010 06:07:30 +0000

but there is no traffic on the trunk link between the two switches (one switch configured with vlan 1 and the other with vlan 2) but there is traffic when both switches are in vlan 1

By: Blog Admin

Blog Admin — Wed, 13 Oct 2010 18:23:56 +0000

For the 2960 the default trunk protocol is dot1q, so you do not need to put the “switchport trunk encapsulation dot1q” command.
So the way you have it is correct now.

By: Felix

Felix — Wed, 13 Oct 2010 17:02:20 +0000

as it stands now start config on the trunk is !
interface GigabitEthernet0/1
description Link to RA-SERVERFARM-S01
switchport mode trunk
speed 1000
duplex full

now, when i try to add the tagging config, this is what i get.

!RA-HQ4FLR-S01(config-if)#switchport trunk encapsulation dot1q
^
% Invalid input detected at ‘^’ marker.

//I TRIED ERASING THE START CONFIG AND RELOADING (RESTART) THE SWITCH AND DO THE CONFIG AGAIN BUT TO NO AVAIL. PLEASE ASSIST.