RVS4000 - No DHCP pass-through across VLANs?

Unanswered Question
Jan 26th, 2010

I built my own gigabit router using FreeBSD on an old PowerEdge 2400 with a few gigabit cards and IPF.  My bosses want a more "turnkey" solution, presumably something they can manage "if I get hit by a truck".  So, I bought the RVS4000 thinking, "gigabit router, should work..".  I come to find out that not only can it not handle multiple IP addresses on the WAN port, but it refuses to allow DHCP to pass through the VLANs, at least in the way I have it set up.

Can anybody give me some tips as to how to get all of my VLANs to talk to the same DHCP server?  Is this thing only designed to be used by "small business owners with no IT training" and thus incapable of more advanced functions?

Thanks!

I have this problem too.
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alissitz Tue, 01/26/2010 - 20:18

Hello and good evening Nate.  I hope you are doing well.

DHCP requests are broadcast and by default will not pass a L3 / vlan boundary.

On the RVS4000 you can set up DHCP relay to relay packets to your DHCP server.  Have you tried this yet?  Have you also configured the vlans?

Here is a link to the user guide:

http://www.cisco.com/en/US/docs/routers/csbr/rvs4000/administration/guide/RVS4000_V10_UG_B_web.pdf

Nate - you mentioned some advanced features.  What additional configs, applications, redundancy etc ... are you all looking for?

Do please let me know if this helps.  Kindest regards,

Andrew

nate.schoolfield Wed, 01/27/2010 - 08:56

Nope, the option for DHCP pass through is greyed out when you specify a VLAN for an interface.

It also doesn't work experimentally, either

As far as advanced features, if you're taking requests (some of these might exist, I haven't had time to fully explore the device):

Commandline interface

IPF-style firewall rules

More robust WAN interface

  • Multiple IP support
  • One-To-One NAT
  • Traffic statistics

I'm using a SonicWall TZ170 for most of these features, but of course it's only 100mb so I can't use it as my internal router (wouldn't want to, anyway).

I mean, I know this is only a $100 router, and all of these features exist on the $5000+ routers Cisco sells, but dangit, I'm not gonna spend $5000 for a router I can build myself for $50 - especially in a small business situation (i.e., no budget).

David Hornstein Fri, 01/29/2010 - 08:34

Hi Nate,

Not that i'm going to debug your dhcpd.conf file, but it would be interesting to see that file, can you please post it ?

I will set up my RVS4000 in the mean time to  so that I and  the wider community can also understand it's functionality.

regards Dave

nate.schoolfield Fri, 01/29/2010 - 09:01

I'm assuming you mean the dhcpd.conf from my FreeBSD box.  I'm using FreeBSD as the router/IDS, but not the DHCP server.  For that I'm using MS Server 2003.

David Hornstein Sat, 01/30/2010 - 21:29

Hi Nate.

DHCP relay works according to the release notes on this software version.

What follows is the results from my ipconfig /all from my XP PC. 

Please note Nate, the default  gateway IP address  is VLAN 1 ip address of  my RVS4000.

The 192.168.1.100 is the IP address of my microsoft small business server, which is providing DHCP services for VLAN1.

        Connection-specific DNS Suffix  . : cisco.com
        Description . . . . . . . . . . . : Intel(R) PRO/1000 PL Network
        Physical Address. . . . . . . . . : 00-1A-6B-67-6C-3D
        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 192.168.1.10
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        IP Address. . . . . . . . . . . . : fe80::21a:6bff:fe67:6c3d%5
        Default Gateway . . . . . . . . . : 192.168.1.1
        DHCP Server . . . . . . . . . . . : 192.168.1.100
        DNS Servers . . . . . . . . . . . : 24.25.5.147
                                            fec0:0:0:ffff::1%1

The following is a screen capture from my RVS4000;

rvs4000.jpeg

Lastly, for the last few releases, the release notes have  stated  that;

DHCP Relay is not supported when  multiple VLANs are created..

(http://www.cisco.com/en/US/docs/routers/csbr/rvs4000/release/notes/Release_Notes_for_Cisco_RVS4000_Version_1.3.0.5.pdf)

I'm guessing this has to be the case because the RVS4000 will not pass VLAN infomation with the DHCP request, so how can a DHCP server provide services for multiple VLAN.

Anyway,  I set up two vlans on my RVS4000, I set a Microsoft small business server to provide DHCP services on VLAN1 at IP address 192.168.100.

I then allowed the RVS4000 to provide DHCP services  to VLAN2.

                                                         All worked ok

I figured that DHCP relay will work on one VLAN, but you have to use the RVS4000 to provide DHCP services to subsequent VLANs.

I do hope this answers your questions.

regards Dave

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