Vlan – Some question about the relationship between VLAN , DHCP and subnet

dhcpsubnetvlan

I am new here and very interested in computer networks. From a book, I have some questions, for which I need help.

question1: Can there be only one working DHCP server in one VLAN?

question2: Can there be only one subnet in one VLAN?

I know that a VLAN can have ports which belongs to several different subnets. So, why can't a VLAN have more than one DHCP server and more than one subnet?

Best Answer

You can have multiple DHCP servers serving a VLAN. The client will use OFFER that comes in first if receiving multiple.

ISC has support for DHCP redundancy while Microsoft was a bit lacking in this department. They have recommended split scopes in the past but it's not really a good solution.

You can have multiple subnets per VLAN. On a Cisco device you would use:

ip address x.x.x.x y.y.y.y secondary

Related Solutions

IPv4 Subnet vs VLAN – Understanding the Differences

If they are used interchangeably then they are used incorrectly.

Subnet refers to particular IP network, such as 192.0.2.0/28.

VLAN refers to 802.1Q standard, in which you can essentially give each port unique MAC address table, effectively separating them from each other.

VLAN may transport one or more subnet (but does not have to, it may be transporting something else than IP entirely). Subnet may be configured for VLAN, but does not have to be, it could be without 802.1Q or over some completely different L2 technology than ethernet.

VLAN and Subnet – Understanding Their Relationship

You can use secondary addressing to add another subnet onto a SVI, this is not recommended but can be used if you really need it.

Current configuration : 190 bytes
!
interface Vlan45
 ip address 2.3.4.5 255.255.255.0 secondary
 ip address 3.4.5.6 255.255.255.0 secondary
 ip address 4.5.6.7 255.255.255.0 secondary
 ip address 1.2.3.4 255.255.255.0
end

Best Answer

Related Solutions

IPv4 Subnet vs VLAN – Understanding the Differences

VLAN and Subnet – Understanding Their Relationship

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