VLAN question

workfrom925workfrom925 Member Posts: 196
in CCNA & CCENT


I did Packet Tracer VLAN activiy 3.5.1. The instruction says to created VLAN 10, 20, 30 and 99 in all three switches. But I didn't create VLAN 10, 20 and 30 in S1， the ping between PCs inside each VLAN works anyway.

So is it necessary to create VLAN 10, 20 and 30 in S1? If not, why not?

Delete .doc from the Packet Tracer file name to run it. Login Pass: cisco. Thanks.



S1#show vlan br

VLAN Name Status Ports
----
1 default active Fa0/3, Fa0/4, Fa0/5, Fa0/6
Fa0/7, Fa0/8, Fa0/9, Fa0/10
Fa0/11, Fa0/12, Fa0/13, Fa0/14
Fa0/15, Fa0/16, Fa0/17, Fa0/18
Fa0/19, Fa0/20, Fa0/21, Fa0/22
Fa0/23, Fa0/24, Gig1/1, Gig1/2
99 Management&Native active
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
S1#
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Comments

  • krjaykrjay Member Posts: 290
    I couldn't open your attached document but are your F0/1 and F0/2 on SW1 set as trunk ports currently?
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  • workfrom925workfrom925 Member Posts: 196
    krjay wrote: »
    I couldn't open your attached document but are your F0/1 and F0/2 on SW1 set as trunk ports currently?

    S1>
    S1>ena
    S1#show int trun
    Port Mode Encapsulation Status Native vlan
    Fa0/1 on 802.1q trunking 99
    Fa0/2 on 802.1q trunking 99

    Port Vlans allowed on trunk
    Fa0/1 1-1005
    Fa0/2 1-1005

    Port Vlans allowed and active in management domain
    Fa0/1 1,99
    Fa0/2 1,99

    Port Vlans in spanning tree forwarding state and not pruned
    Fa0/1 none
    Fa0/2 none
    S1#
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  • WarpigWarpig Member Posts: 32 ■■□□□□□□□□
    I believe your answer is right here.


    Port Vlans allowed on trunk
    Fa0/1 1-1005
    Fa0/2 1-1005


    if your VLans are allowed on the trunk (looks like they are) and the Fa0/1 interfaces in S1 are in fact in trunking mode you should get that result. Where you will have a problem is if you try to hang a machine off of access mode ports on S1 and don't have the appropriate VLan listed in the VLan database.

    So if you don't want machines on VLans 10/20/30 to hang off of S1 no need but if you do, then there is.

    Nick
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  • workfrom925workfrom925 Member Posts: 196
    I see. Thanks. One more thing I learned about switching :)
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  • networker050184networker050184 Mod Posts: 11,962 Mod
    Warpig wrote: »
    I believe your answer is right here.


    Port Vlans allowed on trunk
    Fa0/1 1-1005
    Fa0/2 1-1005


    if your VLans are allowed on the trunk (looks like they are) and the Fa0/1 interfaces in S1 are in fact in trunking mode you should get that result. Where you will have a problem is if you try to hang a machine off of access mode ports on S1 and don't have the appropriate VLan listed in the VLan database.

    So if you don't want machines on VLans 10/20/30 to hang off of S1 no need but if you do, then there is.

    Nick

    That is not true. You need to have the VLAN defined on every switch in the forwarding path. I'm not sure how Packet Tracer works, but on real hardware you will need the VLAN.
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  • WarpigWarpig Member Posts: 32 ■■□□□□□□□□
    So when a switch receives a frame on a trunked interface that it cannot match the vlan id it reads inside the vlan header on the frame from the trunk to it's local vlan database is it supposed to drop the frame or pass it along the trunk anyhow? It sounds like you are saying that it will drop the frame out of the trunk and not pass it along to other switches. I very well may have missed this in my ICND2 reading thus far (I was reading for CCNA but am now focusing on my ICND1 after the announcement of the sept test deadline) :) If so, wouldn't that cause problems? What happens if you replace a switch in the middle of a trunk somewhere? Will it cause data that is attempted to be passed through any of it's trunked interfaces for VLan's other than VLan 1 to be dropped and not reach downstream switches until it has all of the appropriate VLans added to it's database either manually or by VTP? It could take up to 5 minutes for that switch to receive a VTP update from the VTP server no? that would be a LONG time to possibly be dropping ALLOT of data off the trunk. Would the new switch immediately request a VTP update to prevent this? What about VTP transparent mode or if VTP is not in use?

    Nick
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  • prtechprtech Member Posts: 163
    From cisco:
    "By default a trunk link carries all the VLANs that exist on the switch. This is because all VLANs are active on a trunk link; and as long as the VLAN is in the switch's local database, traffic for that VLAN is carried across the trunks."

    Most companies preconfigure the replacement prior to replacing a network device.
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  • WarpigWarpig Member Posts: 32 ■■□□□□□□□□
    prtech wrote: »
    From cisco:


    Most companies preconfigure the replacement prior to replacing a network device.

    Very good point. I suppose unless the switch to be replaced is completely down It would be pretty easy to copy config.text from flash to TFTP Server or better yet get your backup copy of config.text from wherever you save all of your config backups and then pull them via TFTP onto the replacement switch at the desktop. Rebuild your VLan database and minimize your downtime during install.

    "By default a trunk link carries all the VLANs that exist on the switch. This is because all VLANs are active on a trunk link; and as long as the VLAN is in the switch's local database, traffic for that VLAN is carried across the trunks."

    It's funny now that you point out this quote I distinctively remember reading something worded nearly identically to the first part of that statement in one of my books. But I don't remember reading the latter two thirds. lol Well hopefully i will be done with ICND1 soon and back to ICND2 (I find the ICND2 topics far more interesting anyway)

    Nick
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  • leonlimsgleonlimsg Member Posts: 10 ■□□□□□□□□□
    Is there Virtual Trunking Protocol aka VTP being configured on the swtiches?

    VTP can propagate VLAN information to all switches if the switches are in the same domain. Let's say you have VLAN 1 and VLAN 2 in Switch1, with VTP enabled in all switches, all switches will create VLAN 1 and VLAN 2 by themselves. In this way, you don't have to go to every switch to configure the VLANs.

    You can use the command show vtp status to check.

    Switch#sh vtp status
    VTP Version : 2
    Configuration Revision : 2
    Maximum VLANs supported locally : 255
    Number of existing VLANs : 7
    VTP Operating Mode : Server
    VTP Domain Name : MFA1
    VTP Pruning Mode : Disabled
    VTP V2 Mode : Disabled
    VTP Traps Generation : Disabled
    MD5 digest : 0x30 0x5A 0xB6 0x99 0xD5 0x3B 0xD3 0x33
    Configuration last modified by 0.0.0.0 at 3-1-93 00:02:14
    Local updater ID is 0.0.0.0 (no valid interface found)

    Please also note that the connection between the switches must be a trunk.
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