Cisco NXOS Layer 3 Switch, DHCP Relay, Intervlan Routing - How to make it work

Chuntzu

Active Member
Jun 30, 2013
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After almost two days of trial and error (as well as a ton of reading) I am not any closer to solving this problem. I am hoping to get some assistance, in what think is just a fundemental missunderstanding of how intervlan routing, layer 3 functions in nx-os, and placement of router (if needed), trunk ports (for layer 2), and layer 3 switch ports.

End goal: to have 1 dhcp server (windows DHCP,DNS, and Domain Server) give out ip addresses for every vlan, ie vlan2=192.168.2.1/24, vlan3=192.168.3.1/4, etc... Along with that routing between subnets (192.168.1.1/24, 192.168.2.1/24, 192.168.3.1/24) and accessing those resources.

Equipment in question:
3 - lb4m - 48gbe & 2 sfp+
1 - cisco nx3064-x - 48 sfp+ & 4 qsfp+

Layer 3 question:
The first question is with this cisco switch since it is layer 3 I should not need to use a seperate router to ping connections on each subnets correct? I should be able to configure a "no switchport" assign it an ip address in the native vlan subnet (for me 192.168.1.1/24) and set up a dhcp relay (or dhcp ip helper address for ios guys) address pointing to my dhcp server set up the scopes and then volia?

Layer 2 question:
Once the layer 3 interface has been established then I set up svi interfaces, ie vlan 2, ip address 192.168.2.1/24, then when to the ports connecting to the switches and did the trunking commands and allowed all vlans on them. I went to the web interface for the lb4m switches I created and set the vlans for sfp+ ports to include and tab the vlans created on the the cisco switch. Finally I created an ip route of 0.0.0.0 0.0.0.0 192.168.1.1 (with this address being the layer 3 interface created earlier). Is this correct?

In the end I am just looking for 1 DHCP to give out ip addresses for each scope and for the routing to be handled by the 10gb switch and pass the vlans to the lb4m switches. Thank you for any guidance.
 

azev

Active Member
Jan 18, 2013
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I never worked with N3K but have plenty of other Nexus flavored switches at work. For what I can tell, even at the most basic level licensing static L3 is supported.
When you create multiple SVI on a switch, it will does all the routing you need between the SVI's.

For nexus, the dhcp relay command is : " ip dhcp relay address x.x.x.x" you want to add this command in each of the SVI.

I am not familiar with LB4M switch, but generally what you are trying to do is correct, maybe things aren't working because you have the wrong gateway IP ? (SVI = 192.168.2.1, static route pointed to 192.168.1.1) ??