Tag: dhcp

Forwarding UDP broadcast traffic mechanisms

We will speak here about some basics about Forwarding UDP broadcast traffic. If you were wondering what Forwarding UDP broadcast traffic actually is I will try to explain it here in few words.

If you have more that one broadcast domains in your local network, let’s say that you have three VLANs. In normal networking theory it’s normal that broadcast initiated on host inside one VLAN will get to all host inside that VLAN but it will not get across to other VLAN. Typically the broadcast domain border is router or a Layer’s 3 switch VLAN interface. Although this is normal for most of broadcast traffic there needs to be a way to forward some kinds of broadcast traffic across that border. Why? Here’s a simple example. If you use DHCP, and you are, you will probably have hosts in different VLANs and all of them need to get the IP address from DHCP. If Forwarding UDP broadcast traffic didn’t exist it will be needed to have one DHCP server on every VLAN. Remember that DHCP works using broadcast traffic in some of the steps.

Simple DHCP address leasing:

Host that connects on the network will in the first step send broadcast DHCP discover message in order to find where the server is or if the server actually exist. After the HDCP replies with unicast DHCP offer host will one again use broadcast to send DHCP request to server. Server will then acknowledge the IP address leasing with unicast ACK message and that’s it.

 DHCP steps

Forwarding UDP broadcast traffic

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IPv6 – SLAAC EUI-64 Address Format

UPDATE on 22 Mar 2018:
Article is correctly describing what is SLAAC and why is needed and describes how SLAAC uses RFC 2373 to generate interface IPv6 address. The thing is that today RFC 7217 describes an enhanced new way of SLAAC algorithm to improve user security and protect hosts from attacks. Details are available here in my new article about SLAAC.

Stateless autoconfiguration or SLAAC

SLAAC is a method in which the host or router interface is assigned a 64-bit prefix, and then the last 64 bits of its address are derived by the host or router with help of EUI-64 process which is described in next few lines. SLAAC uses NDP protocol to work.ipv6

As the format of the EUI-64 format is seen quite frequently, covering its details seems important too.

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DHCP – Dynamic Host Configuration Protocol

DHCP – Dynamic Host Configuration Protocol is a configuration protocol for the host’s set of connections on the IP networks. Obviously, computers within IP networks should be configured to communicate with each other. But some other information is needed to understand the mechanical of online communication such as IP (internet protocol) addresses, default routes and prefixes. DHCP protocol will let you to get rid of manual handling of certain tasks with a network administrator’s help. A central database should be connected to a network, if this protocol incorporated into it so the chances relating duplicating resource assignments can be eliminated.

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