DHCP Options in VMware SD-WAN by VeloCloud Edges

Products

• VMware SD-WAN by VeloCloud

Issue/Introduction

The ideal way to configure DHCP Options, if Edge is serving as DHCP server, for a VLAN.

Environment

VMware SD-WAN by VeloCloud

Resolution

Below are the Default DHCP parameters returned in DHCP Offer Packet, for any DHCP Discover:

 

1 - Subnet Mask

3 - Default Router for this network (== the edge)

6 - The DNS server to use (usually us, unless overridden by Default option 6)

15 - The DNS domain to set on the client (usually 'lan', unless overridden by customer's option 15)

28 - Broadcast Address

53 - "ACK" (the response type, which is itself an "option")

54 - DHCP server identifier == address of server that is sending back the response

51 - IP Address Lease Time == seconds

58 - Renewal Time Value

59 - Rebinding Time Value

Along with the above DHCP parameters, we also have few “Pre-Defined” DHCP options which are configurable in the Orchestrator's UI under “VLAN Settings -> Edit”, as shown below.

• If it’s required to “pass / send” any other DHCP options other than the default or Pre-Defined Options, you need to configure Custom DHCP options, as highlighted in blue above.
• “Code” is the value of the DHCP option, as per IEEE standard. (Ex: “6 for DNS”, “132 for VLAN” & So on)
• By default, there are 2 “Data Type” ways to pass / Send, the “Custom Options” if any are configured i.e.

Text

If option that needs to be returned is “IP address” (or) Hexadecimal value, the Data Type should be “TEXT”

Example: For Voice VLAN’s, it’s required to send “Options 129 - Call server IP address”, this should be defined as Custom DHCP option and passed as Text (as it’s not listed in Predefined Options on UI), Value entered should be in same format like an IP address

• “dnsmasq” understands the value being passed is an IP address, but please ensure when Value is entered with “No Spaces or quotes” used.
• Secondly if value to be returned is a “Hexadecimal” value, for example “MITEL Phones” need’s Options “132 & 133 i.e (Vlan and QOS) values” to be returned in Hexadecimal, data type is again “TEXT”
•  Use Colon “ : ”, to separate the Hexadecimal value,  

Example: A customer's Phone service needs VLAN & QOS values sent by DHCP server, as Options “132 & 133” in Hexadecimal format, as shown below with Colon:

Number

-> If any end device requires the values to be returned as “Decimal”, then Data Type should be configured as “Number”

These options will only be returned if requested in “DHCP Discover” by the end Client in Option-55, as shown below, otherwise only the Default parameters would be returned,

Option 6, DNS servers

Use a single entry for option 6, if a primary/secondary DNS server are needed, enter both in option 6 separated by a comma.

Example:  8.8.8.8,8.8.4.4

If two separate Option 6 entries are used, the client will only be configured with one of them.