Router on the stick configuration problem

Discussion in 'Cisco' started by Guan Foo Wah, Oct 23, 2005.

  1. Guan Foo Wah

    Guan Foo Wah Guest

    Hi all,

    I have some problem configuring router on the stick. Basically, here is the
    configuration on my router 2612 router running on 12.2(31) IP Plus. This
    router is attached to a Cat 2950 and its attached port is configured as
    "switchport mode trunk"

    interface ethernet0/0
    no ip address
    half-duplex
    interface ethernet0/0.1
    encapsulation dot1Q 1 native
    ip address 10.0.0.41 255.255.0.0
    interface ethernet 0/0.2
    encapsulation dot1Q 2
    ip address 10.16.0.41 255.255.0.0

    Members in vlan 2 can ping 10.16.0.41 but members in vlan 1 cannot ping
    10.0.0.41. If I change the configuration to this....
    interface ethernet0/0
    ip address 10.0.0.41 255.255.0.0
    half-duplex
    interface ethernet 0/0.2
    encapsulation dot1Q 2
    ip address 10.16.0.41 255.255.0.0

    Members in vlan 1 have no problem pinging to 10.0.0.41 and members in vlan 2
    have no problem pinging 10.16.0.41. Any idea on what is happening? Both
    configuration are supposed to be valid and workable and but apparently the
    upper configuration is not working all all. Thanks in advance.
     
    Guan Foo Wah, Oct 23, 2005
    #1
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  2. Guan Foo Wah

    Cen Guest

    Most likely you have encountered a Cisco bug (Bug ID CSCds42715). Refer to
    http://www.cisco.com/warp/public/473/50.shtml for more info.




    "Guan Foo Wah" <> wrote in message
    news:435ba5ed$...
    > Hi all,
    >
    > I have some problem configuring router on the stick. Basically, here is
    > the configuration on my router 2612 router running on 12.2(31) IP Plus.
    > This router is attached to a Cat 2950 and its attached port is configured
    > as "switchport mode trunk"
    >
    > interface ethernet0/0
    > no ip address
    > half-duplex
    > interface ethernet0/0.1
    > encapsulation dot1Q 1 native
    > ip address 10.0.0.41 255.255.0.0
    > interface ethernet 0/0.2
    > encapsulation dot1Q 2
    > ip address 10.16.0.41 255.255.0.0
    >
    > Members in vlan 2 can ping 10.16.0.41 but members in vlan 1 cannot ping
    > 10.0.0.41. If I change the configuration to this....
    > interface ethernet0/0
    > ip address 10.0.0.41 255.255.0.0
    > half-duplex
    > interface ethernet 0/0.2
    > encapsulation dot1Q 2
    > ip address 10.16.0.41 255.255.0.0
    >
    > Members in vlan 1 have no problem pinging to 10.0.0.41 and members in vlan
    > 2 have no problem pinging 10.16.0.41. Any idea on what is happening? Both
    > configuration are supposed to be valid and workable and but apparently the
    > upper configuration is not working all all. Thanks in advance.
    >
    >
    >
    >
    >
     
    Cen, Oct 24, 2005
    #2
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  3. Guan Foo Wah

    Surfraz

    Joined:
    Jan 5, 2010
    Messages:
    1
    Why did you configure "half duplex"...

    This may be the reason of why only one vlan can ping in the trunk, as its using shared wire

    If you configure full duplex on the subinterface, it should work
     
    Surfraz, Jan 5, 2010
    #3
  4. Guan Foo Wah

    donjohnston

    Joined:
    Jun 28, 2008
    Messages:
    38
    I have had more problems trying to trunk an ethernet (10m) port than not.

    My opinion is, use a fastethernet interface.
     
    donjohnston, Jan 15, 2010
    #4
  5. Guan Foo Wah

    joshstout

    Joined:
    Nov 7, 2010
    Messages:
    1
    The reason for this behavior is that 2950 switches do not tag the native vlan as they use DOT1q by default.

    If you issue a "debug arp" on the router in this scenario while pinging from the router to a device on the switch in vlan 1... you can see that the router responds with a message stating it did in fact recieve an arp reply but filtered it as it came in on the main interface instead of the sub-interface.

    This again, is because the switch did not tag the arp reply and thus it arrives on the physical interface.

    While all of this may make sense, I am confused as to why the router doesn't logically route the untagged traffic into its interface tagged with the "native" keyword.

    Hope this helps,
     
    joshstout, Nov 7, 2010
    #5
  6. Guan Foo Wah

    nover

    Joined:
    Nov 15, 2010
    Messages:
    5
    thanks for useful information...
     
    nover, Nov 15, 2010
    #6
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