On 802.1Q Trunk, does CDP send its frame tagged with VLAN 1 info or untagged when native VLAN on a trunk is not 1?
My understanding is that if native VLAN on a trunk is 1, CDP will send its frame untageed. However, if native VLAN on a trunk is not 1, CDP will always send its frame tagged with VLAN 1 tag. To make sure, I did test on the Packet Tracer 7.1 and the lab was successful.
Recently I had a chance to ask some questions to the CCIE Routing&Switching holder. He said, "Since DTP and CDP packets do not get forwarded, there is no need to tag VLAN info. However, VTP packets do get forwarded and loop might be occurred. That's why VTP is always forwarded on trunks with a VLAN 1 tag unless the native VLAN on a trunk is 1." He indeed showed me that CDP always sends its frame untagged even if the native VLAN is changed to something else than 1 with EVE simulator.
So my questions are:
1. If you can understand him, could you please explain to me why loop might occur if VTP packets get forwarded untagged?
2. If you have real switches or VIRL, could you please test whether CDP sends its frame tagged with VLAN 1 tag or untagged when native VLAN on a trunk is not 1? I really love to test myself, but I don't have real switches and my computer is way behind from VIRL hardware requirements.
Inviting all network professionals in operations! We'd like to understand what would be valuable for you in a mobile application. Your response will help Cisco improve a product feature that could benefit you. Thanks!
Click here to take the sur...
Cisco’s software-defined wide area network (SD-WAN) solution allows user to quickly and seamlessly establish an overlay fabric to connect an enterprise’s data centers, branch and campus locations, as well as colocation facilities in order to imp...
1. Log into CLI of DNAC:
ssh maglev@< DNAC appliance IP> -p 2222
2. Run this curl command to get token to get member id:
curl -X POST -u admin:<admin user password> -H -V https://<CLUSTER-IP>/api/system/v1/identitymgmt/token
Enterprise Switching Business Unit is glad to announce Beta release 16.12.2 for all Catalyst 9200/9300/9400/9500/9600 and Catalyst 3650/3850 Platforms. This release is made available to allow users to test, evaluate and share fee...
Purpose of the document
This document describes the general recommendations or best practices when designing and deploying the Cisco SD-Access technology. The document assumes that the reader has a general overview of Cisco's SD-Access for Distributed C...