Can't add IP Helper-Address to VLAN & Why is RIP not available?

[cre8toruk]

Hi all,

after an afternoon of trawling I figured I'd jus ask and hope you bright lot can help me out.

I'm commissioning a new network for my company... I'm ok with most stuff and have built the network in Packet tracer all lovely.

Now when it comes to it I'm having some trouble with some basic stuff.

I have a pair of 350XG's stacked.. I'm trying to add an ip helper-address to my endpoint VLAN so they can go grab a DHCP ip address from our domain controller.

Endpoints on VLAN 200 (IP: 192.168.200.0) DHCP server on 192.168.10.101... So I do the following;

int vlan 200
ip helper 192.168.10.101
% missing mandatory parameter

This returns me the error above.... can anyone tell me what I'm doing wrong?

I also wondered why it was that I couldn't do the following;

router rip
version 2
network 192.168.10.0
network 192.168.200.0
network 192.168.254.0
redistribute connected
redistribute static

it seems rip isn't available on this switch?

Any ideas anyone?

thanks in advance,

Paul.

[Jaderson Pessoa · Accepted solution]

@cre8toruk Hello,

You can use a DHCP relay configuration as below;

ip dhcp relay enable
ip dhcp relay address 1.1.1.1
ip dhcp relay address 2.2.2.2

interface vlan 10
ip dhcp relay enable

interface vlan 20
ip dhcp relay enable

look more information here: https://www.cisco.com/c/pt_br/support/docs/smb/switches/cisco-small-business-300-series-managed-switches/smb5567-configure-dynamic-host-configuration-protocol-dhcp-relay-set.html

About RIP, this switch do not support this feature, look here: https://www.cisco.com/c/en/us/products/collateral/switches/small-business-smart-switches/data-sheet-c78-737359.html

[cre8toruk]

Thanks jaderson.. I'm hoping that it doesn't matter and the inter vlan routing will work anyway, is that your understanding ?

[cre8toruk]

Hi Jaderson, sorry just for my reference what is the missing mandatory parameter I'm err missing?

[Jaderson Pessoa]

Hello, on this platform "SG", you need use as i told to you... in cisco catalyst family, your old command will works :)

[Leo Laohoo]

How can you configure an IP Helper Address if the VLAN itself doesn't have an IP address?
Think about the logic:
1. How will the DHCP server know what subnet the request is coming from?
2. How will the DHCP server know WHERE to send the request to if the VLAN doesn't have an IP address?

[cre8toruk]

The vlan does have an ip address 192.168.10.254 and 192.168.200.254 for vlans 10 and 200 respectively

[cre8toruk]

Right, so I've discovered what I was doing wrong....

Apparently the syntax of the ip helper-address command requires a source and a destination and apparently you can also specify a UDP port for DHCP (68 I believe), however when I try that it tells me it's reserved.

e.g.

ip helper-address All 192.168.10.10
ip helper-address 192.168.200.0 192.168.10.10

both work...in that I don't get any errors :-)

In any case with Jaderson's help I hope that I won't need this to work. It would appear on the surface that it's been superseded by the ip dhcp relay command.

[Georg Pauwen]

Hello,

on a side note, I think RIP actually is available on the SG350X, you just cannot add it through the command line, but you have to use the GUI. Check page 396 (chapter 17) of the attached admin guide...

https://www.cisco.com/c/dam/en/us/td/docs/switches/lan/csbms/350xg/admin_guide/AG_Tesla_350_550.pdf

[cre8toruk]

Hi thanks for this... I've had a look but I can't see the RIP v2 option...

[cre8toruk]

Actually reading the page it specifies it's only available on the 550xg tcch!I suppose it really matters, so long as it routes stuff!

[Georg Pauwen]

My bad...sorry for the (mis)information...I should have read it better myself before posting the link...

[Jaderson Pessoa]

as i told to you.. this model doesnt support dynamic route protocol :)

[Jaderson Pessoa]

Sure, as i have suggested to you.. you wont need this under interface if you are using dhcp relay method applied at SG familly.

Regards