07-29-2008 10:10 AM - edited 03-06-2019 12:30 AM
I have discovered a problem with my newotk on one particular vlan. The problem started
with a dhcp issue. No clients whatsoever could get a ip address from vlan2 on the switch,
but there were no problems with the other vlans. The router itself acts as a dhcp server
for all vlans, including the one i have problems with. Vlan2 has the exact same configuration
as vlan3, and that one i have never had any issues with.
During troubleshooting i connected a client directly to a accessport on the 1812 router, and
voila! It recieved a ip address. This makes me believe that the configuration itself is good.
I have some sort of trunk issue, for the 1812 router and 2960 switch is conencted via a trunk.
Now i borrowed a 1841 router to act as a client. And i discovered a strange thing. First the setup:
Physical setup:
1812(fa2) ----- 2960(fa0/8)
2960(fa0/4) ----- 1841(fa0/0)
Configurations:
1812:
interface FastEthernet2
switchport mode trunk
2960:
interface FastEthernet0/4
switchport mode trunk
1841:
interface FastEthernet0/0
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.2
encapsulation dot1Q 2
ip address 10.100.2.250 255.255.255.0
!
interface FastEthernet0/0.3
encapsulation dot1Q 3
ip address 10.100.3.251 255.255.255.0
With this setup i can ping the vlan2 interface (10.100.2.252/24) on the switch from the 1841,
but not the default gateway on the 1812 router for vlan 2 (10.100.2.254/24). But i can however
ping the default gateway for vlan 3 on the router (10.100.3.254/24)!!!
If i connect the 1841 router with the same config, directly to the 1812 trunk interface, fa2,
everything works!
I have no clue whatsoever right now, i hope someone can help me.
07-29-2008 11:36 AM
Hello Frederik,
when using 802.1Q trunks a possible problem is a mismatch in the native vlan
check the C2960 ports with
sh interface fas0/4 switchport
sh interface fas0/8 switchport
verify encapsulation, native vlan, list of vlans permitted and in forwarding state
both vlan 2 and vlan 3 must be permitted on both trunks
on the router you can use debug vlan packets
+ term monitor
Hope to help
Giuseppe
07-29-2008 12:17 PM
Hi,
Thanks for your reply. The trunk port configuration on both the router and switch are as you can se in my first message simple, and exactly alike. The trunk works, but not for accessports on the switch. "sh ip int brie" shows up/up for vlan 2 for example.
//F
07-29-2008 12:47 PM
Hello Frederick
for access-ports
switchport mode access
switchport access vlan 2
the default is 1
Hope to help
Giuseppe
07-29-2008 01:11 PM
Hi,
Yeah, i know. But that is not the issue.
//F
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