Errors on Router Lan Interface......

[norrie108]

I have a 1751 Router (Version 12.1(5)YB4) connected to a 2970 Switch (Version 12.2(25)SEB2), when I create a sub-inter face on the Router it accumulates errors (10% approx), the interfaces were configured with fixed speed and duplex settings and to trunk (dot1q), when I stripped back the sub-interface from the router and made the switch interface switchport access it works fine. This is not ideal as I do require the interfaces to be set to switchport mode trunk. Any ideas?

Thanks.

[lgijssel]

Just a few tips:

1: Did you use switchport nonegotiate on the 2970 trunk?

2: Were the vlans for which you had the subinterfaces defined also present on the 2970?

3: Are you able to upgrade the 1751 to a more recent release?

Hope this helps,

Regards,

Leo

[norrie108]

Hi Leo,

1) No I did not use switchport nonnegotiate, I stipulated switchport mode trunk.

2)Vlan was present on the 2970

3)Yes I can upgrade but I’m not so sure that this is the problem.

The only WAN Service that was affected was Exchange all other applications that users access via this WAN interface was operating ok?

Thanks

Norrie

[lgijssel]

Are you using the same vlan as native on both sides?

Is the native vlan set identically on both sides? (tagged or untagged)

Regards,

Leo

[norrie108]

The Vlan (at present) is only significant locally and is not asigned as native.

Regards

Norrie.

[lgijssel]

It seems as if you do not understand the point. There are two ways to transport packets between vlan capable devices. The most well known method is by using dot1Q encapsulation, the vlan-tag contains the vlan id. For compatability reasons the standard also involves the possible use of untagged traffic. This is done over the native vlan.

Problems can arise when one side is expecting untagged traffic but receives the traffic with a tag or vice versa. On switches, you can configure this by setting the native vlan on a port. On routers this is also the case, you are configuring the vlan id on the sub-if. The native vlan can be configured on the physical interface in which case it's traffic is not tagged. By not configuring this, you are tagging all vlans. On switches, you must configure the native vlan to be tagged if you want this. The default is: vlan 1 = native = untagged

Both sides must be set identical, no data can be exchanged otherwise.

Regards,

Leo

[nethelper]

Hello,

since you say that Exchange traffic is affected, there might be a problem with the MTU or MSS settings. Try and configure the following on your LAN (sub)interfaces and check if that makes a difference:

ip tcp adjust-mss 1350

Regards,

Nethelper