CRC Errors on Switch when using LAN subinterfaces

[#1]

Hi, I have configured a Fortigate 100A DMZ1 interface with 3 subinterfaces (VLANs 1, 20, 21) and when I attempt to configure the switch port (Cisco 3548 switch) as a dot1q trunk, I get nothing but input/crc errors. The strange thing is that this interface works ok when only the physical interface is in use (Vlan 1 on switch and configured as an access port) and it works ok on a different Fortigate unit that I have. The switch doesn' t have any special configurations - mainly ports associated with VLAN 1 and I created VLAN 20 and 21 in the vlan database and assigned the port to the FG100A as a trunk port! Yet when I put the physical port back in VLAN 1 it works fine! Any suggestions/ideas? Cheers, Michael

[mhe]

Seems to me like an MTU problem.... dot1q requires some bytes and vlan tagging too. had this problem once and didn' t find a solution (maybe setting the global mtu is a solution but we haven' t tested this...). martin

[#3]

It could well be - I' ll have a play around with the MTU settings and see if that makes a difference. Cheers Michael

[#4]

i' m having quite different situation but generated CRC and Input error. I do realise, when connecting fortigate with my 3com switch, i' ve set both peering port to static 100full and both interface work without any error. But connecting fortigate to cisco, i' ve to set both peering port to auto, then it work with full duplex port capability.