Which vlan does cdp use

If this sub-if was disabled advertisements were not processed and show neighbors displayed nothing. There are multiple sub-ifs in the up up state, but know of these sub-ifs would process the cdp advertisement. Only the dot1q native sub-if will. The question s are Will cdp only send an advertisement encapsulated in non tagged Ethernet frames? Does cdp require native vlans to be configured on every device?

CDP frames can be sent tagged or untagged. I think it is better for you to read directly from the linked CIsco tech note that explains the behavior pretty well and is specifically written for your scenario - a switch sending traffic to a router using sub-interfaces.

The Cisco document linked above is for general purpose routers and switches running IOS. Whether it is tagged depends on configuration on either devices. The switch will receive the CDP packets from the router but because you disabled the router's VLAN 1 sub-interface, the router will drop the incoming CDP packets since the interface it sends all untagged frames to is shut down. The router will receive the untagged CDP packets coming from the switch though, since there is now a configured sub-interface in the up state that is set as the native VLAN.

From a Security standpoint you would not want to change the native VLAN on a router to be a sub-interface used for data traffic. In your case it is because someone created a sub-interface on the router for VLAN 1 and shut it down, probably because they though it would make the network more secure - it doesn't. You should always have a manually configured VLAN allowed list on a switch trunk port when the connected device is a router without the native VLAN 1 in that allowed list.

CDP will be sent as untagged only and it will be recieved by the physical interface not by sub interfaces so in all cases it will be recieved. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Learn more. Normally that would make sense yes but CDP is a strange animal. I keep hearing and reading about Native vlan for over many years so far but till now and honestly speaking Im not able to understand one thing. What is the benefit or the reason for being Native Vlan in the first place? I read your lesson about Vlan Hopping which is really good with no doubt but still I need to know what is Native Vlan used for in the first place.

In plain English , what is the job of Native Vlan? For many of my locations, users have a single network connection to their desk.

Both of these devices use the single network connection. The connection goes to the VOIP phone, and the computer plugs into another port on the phone. The reason for this is because the VOIP phone can read and understand By configuring the Native vlan as the PC Data vlan, this means the PC gets an untagged frame, so it knows what to do with it.

Thanks for your very nice article. I think,I have find the right one and thats you. So, Is there any use of Default vlan like Native??? Many Thanks. In other words, is it okay to disable, or filter out VLAN 1? The answer to this is it is okay to do this.

In fact, for security purposes, most people avoid using VLAN 1 entirely. How can you capture the frames passing through the trunk by using Wireshark? As far as I know, the capturing tool Wireshark is supposed to be installed in a server. CDP Version-2 CDPv2 is the most recent release of the protocol and provides more intelligent device tracking features.

These features include a reporting mechanism which allows for more rapid error tracking, thereby reducing costly downtime. VLAN Trunking Protocol VTP is a discovery technique deployed by switches where each switch advertises its management domain on its trunk ports, its configuration revision number, and its known VLANs and their specific parameters.

A switch can be configured to be in only one VTP domain. CDP is enabled on Cisco routers by default. If you prefer not to use the CDP capability, disable it with the no cdp run command. In order to reenable CDP, use the cdp run command in global configuration mode. You can verify whether CDP is enabled or disabled on your Cisco device using the show cdp neighbors command. This command output indicates that CDP is enabled on the device, but no neighbor devices are discovered or connected to this device.

The show cdp neighbors detail and show cdp entry commands displays additional information about the neighboring devices that include network-layer protocol information and version. When CDP is enabled globally using the cdp run command, it is enabled by default on all supported interfaces except for Frame Relay multipoint subinterfaces to send and receive CDP information.

Disable CDP on the Serial 1 interface and verify if the neighbor device is discovered on the serial 1 interface, as this output shows:.