duplex mis-match 4500 router

[wzschirnt]

We started logging errors and saw a bunch of "Duplex Mis-Match" errors coming from our 4500 router. It has an Ethernet NIC - not a Fast-Ethernet - so I see no way to change the Duplex parameter.

What's causing this and how to correct?

Thanks.

 

[ADB100]

The chances are this is a result of CDP and a Layer-2 Multicast CDP message from probably a switch is being seen by the 4500 router. What is the physical layer-2 connectivity from the 4500 Ethernet interface? (i.e. is it connected to a hub and then maybe a switch etc?)

Andy

 

[wzschirnt]

The Ethernet port on the router connects to a PacketShaper machine (for filtering and monitoring activity) and then to a 3Com 3300 switch. The PacketShaper shows (by lights) 10mb in and 100mb out (can't tell what duplex right off-hand) to the switch. The port on the switch for this connection from the PacketShaper is 100mb FD.

The Duplex Mis-match says that the Ethernet on the 4500 router is "half-duplex". I can't see that info in any of the router configs and don't see any commands to change the duplex setting (old IOS or the fact that it is an "Ethernet" port and not a "Fast Ethernet"?).

Ideas how to fix this?

Thanks for your time on this.
Walt Z.

 

[ADB100]

Can you post the output from 'show cdp neigbors' - see if there are any other Cisco devices connected to the 3Com switch?

Andy

 

[wzschirnt]

Here's the output.

GrandPrairie#sh cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater

Device ID Local Intrfce Holdtme Capability Platform Port ID
WRSFOT01.alldata.Eth 0 127 R 1720 Fas 0
SFFT Ser 0.4 161 R 2620XM Ser 0/0.1
PPIOKC Ser 0.10 156 R 2500 Ser 0.1
SFOT Ser 1 128 R 2500 Ser 1
SFMW Ser 0.13 166 R 2500 Ser 0.13
EV_SEATTLE Ser 0.26 147 R 2500 Ser 0.1
SFGA Ser 0.8 143 R 2500 Ser 0.1
SFNO Ser 0.28 121 R 1760 Ser 0/0.1
SFMA Ser 0.6 144 R 2500 Ser 1.1
SFOG Ser 0.3 164 R 2500 Ser 0.1
SFNE Ser 0.17 122 R 2500 Ser 0.1
gFRLaronde Ser 0.27 170 R 1720 Ser 0.11
Reino_Aventura Ser 0.25 157 R T 2500 Ser 0.1
Switch Eth 0 167 T S WS-C2924-XFas 0/1
PPIDL Ser 0.16 123 R 2500 Ser 0.1
SFGRA Ser 0.7 166 R 2500 Ser 0.1
PPIAM Ser 0.15 150 R 2500 Ser 0.1
SFAW_core Ser 0.2 164 R 2610 Ser 0/0.1
PPIKK Ser 0.12 178 R 2500 Ser 0.12
SFLAB_POS Eth 0 171 R S I 1841 Fas 0/0
PPIGE Ser 0.19 146 R 1720 Ser 0.1
PPIEG Ser 0.11 130 R 2500 Ser 0.11
PPIWL Ser 0.21 129 R 1602 Ser 0.1
PPINY Ser 0.18 177 R 1602 Ser 0.1
GrandPrairie#
---------------------------------

The WRSFOT01 and the SFLAB_POS are the ones reporting the duplex mis-matches.

Not sure this is the way to post output like this. If there is another way, let me know.

Thanks for your help.
Walt Z.

 

[ADB100]

That pretty much explains it then. The WRSFOT01 is a 1720 router with a Fast Ethernet interface and the SFLAP_POS is a 1721 with a Fast Ethernet interface, these must be connected to the 3Com switch but running at 100Mb/Full-Duplex. What is happening is the Multicast CDP messages are being passed through the 3Com switch and are reaching the 4500, the 1720 and the 1721 Ethernet Interfaces, but you have a duplex mismatch as far as the Cisco devices are concerned. Within the CDP messages are information about the connected interface - 100Mb/Full-Duplex and 10Mb/Half-Duplex, hence the error message you are seeing.

To workaround this disable CDP on the 4500 Ethernet Interface. If you replace the 3Com switch with a Cisco one the CDP messages will be terminated at the Cisco interface they are received on. The 3Com switch forwards the CDP Multicasts (actually floods them to all ports in the VLAN) so you 'see' multiple Cisco devices on the Ethernet.

HTH

Andy

 

[wzschirnt]

I put in a "no enable cdp" on the Ethernet port and the errors stopped.

Thanks for your help.