Trunking is means of transporting multiple VLANs over a single link. This is done by the tagging the frames according to which VLAN they belong to at both ends of the trunk so they can be separated at the other end. If 10 VLANs are being trunked, how many need to be tagged? Just nine, because both ends agree that the untagged VLAN is the native VLAN. Since both ends believe that any untagged frames belong to the VLAN that is configured as the native VLAN, you can see this could cause some serious problems if different VLANs are configured as the native VLAN at each end of the trunk. Native VLAN mismatches can also cause some really nasty bridging loops in a large switched enviorment if you get multiple Spanning Tree negotiations going at the same time. Dave Swink -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Guest Sent: Tuesday, September 04, 2001 10:31 PM To: [EMAIL PROTECTED] Subject: what is the native vlan function in trunk? [7:18543] Hi all,in a trunk,both sides setting as : trunk mode:desirable encapsulation:isl i only try one side native vlan as 1 and the other is 2,except some error messages,everything is still working Console> (enable) 2001 Aug 25 20:29:03 %CDP-4-NVLANMISMATCH:Native vlan mismatch d etected on port 2/48 2001 Aug 25 20:29:05 %DTP-5-TRUNKPORTON:Port 2/48 has become isl trunk 2001 Aug 25 20:29:19 %PAGP-5-PORTTOSTP:Port 2/48 joined bridge port 2/48 Console> (enable) ping 10.0.0.1 10.0.0.1 is alive Console> (enable) show trunk 2/48 * - indicates vtp domain mismatch Port Mode Encapsulation Status Native vlan -------- ----------- ------------- ------------ ----------- 2/48 desirable isl runking 1 Port Vlans allowed on trunk -------- --------------------------------------------------------------------- 2/48 1-100 Port Vlans allowed and active in management domain -------- --------------------------------------------------------------------- 2/48 1-3 Port Vlans in spanning tree forwarding state and not pruned -------- --------------------------------------------------------------------- 2/48 1-3 when i am using the same configuration except the encapsulation is dot1q,the dtp can still construct the trunk,and some error messages displays as follows: Console> (enable) 2001 Sep 04 20:41:41 %CDP-4-NVLANMISMATCH:Native vlan mismatch detected on port 2/48 2001 Sep 04 20:41:43 %DTP-5-TRUNKPORTON:Port 2/48 has become dot1q trunk Console> (enable) 2001 Sep 04 20:41:55 %PAGP-5-PORTTOSTP:Port 2/48 joined bridge port 2/48 2001 Sep 04 20:41:58 %SPANTREE-2-RX_1QPVIDERR: Rcved pvid_inc?inconsistency) BPDU on 1Q port 2/48 vlan 2 2001 Sep 04 20:41:58 %SPANTREE-2-RX_BLKPORTPVID: Block 2/48 on rcving vlan 2 for inc peer vlan 1 2001 Sep 04 20:41:58 %SPANTREE-2-TX_BLKPORTPVID: Block 2/48 on xmtting vlan 1 for inc peer vlan now i cant ping the peer ip . what i want to know is what is the function of the native vlan,what payload it carries,during my testing ,cdp,vtp,dtp is not affected,just the stp.I read the trunk format,in isl,it contain the stp information,in dot1q,the stp info is transfer in native vlan. is that the reason. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=18557&t=18543 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
