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4500X not receiving CDP from C3850 Neighbours

d.kirkham
Level 1
Level 1

Hi,

I have a problem where a 4500X switch is not receiving CDP from all the interconnects C3850 switches. The network is strictly a star with the 4500X forming the core, and the 3850s the access layer. This part of the network is purely Layer 2 with VLANs and management is in-band through vlan 1100.

The 4500X is running 3.6.4E while the 3850s are running 3.7.1E.

The access 3850s are receiving and displaying CDP from the core switch and other connected devices (mostly access points and phones), but the problem is the 4500X is showing nothing:


core-4500#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID

Total cdp entries displayed : 0

core-4500# show cdp
Global CDP information:
        Sending CDP packets every 60 seconds
        Sending a holdtime value of 180 seconds
        Sending CDPv2 advertisements is  enabled

core-4500#show cdp traffic

CDP counters :
        Total packets output: 4963, Input: 0
        Hdr syntax: 0, Chksum error: 0, Encaps failed: 0
        No memory: 0, Invalid packet: 0,
        CDP version 1 advertisements output: 0, Input: 0
        CDP version 2 advertisements output: 4963, Input: 0

... and on the access switches:
access-3850#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone,
                  D - Remote, C - CVTA, M - Two-port Mac Relay

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID

core-4500.dcn    Ten 1/1/3         171             R S I  WS-C4500X Ten 1/31
... lots of other devices...

access-3850#show cdp traffic
CDP counters :
        Total packets output: 327660, Input: 128461
        Hdr syntax: 0, Chksum error: 0, Encaps failed: 0
        No memory: 0, Invalid packet: 0,
        CDP version 1 advertisements output: 0, Input: 0
        CDP version 2 advertisements output: 327660, Input: 128461

I suspect the problem has something to do with tagging of the CDP packets, and nothing being exposed to receive them, but it is unclear to me how I resolve this problem in this otherwise pure Layer 2 fabric.

I've included below a precis of the 4500X configuration. Any tips on how to get CDP showing the access switches would be appreciated.

Thanks,

Daniel

!
version 15.2

!
boot-start-marker
boot system flash bootflash:cat4500e-universalk9.SPA.03.06.04.E.152-2.E4.bin
boot-end-marker
!
!
vrf definition mgmtVrf
 !
 address-family ipv4
 exit-address-family
 !
 address-family ipv6
 exit-address-family
!

!
spanning-tree mode pvst
spanning-tree extend system-id
spanning-tree vlan 1-4094 priority 8192
!
vlan internal allocation policy ascending
!
vlan 2-1001,1006-4094
!
interface FastEthernet1
 vrf forwarding mgmtVrf
 no ip address
 speed auto
 duplex auto
!
interface TenGigabitEthernet1/1
 switchport mode trunk
 mtu 9198
!

!
interface TenGigabitEthernet1/32
 switchport mode trunk
 mtu 9198
!

!
interface TenGigabitEthernet2/1
 switchport mode trunk
 mtu 9198
!

!
interface TenGigabitEthernet2/8
 switchport mode trunk
 mtu 9198
!
interface Vlan1
 description - not used -
 no ip address
 shutdown
!
interface Vlan1100
 ip address 10.11.0.1 255.255.255.0
!

3 Replies 3

Mark Malone
VIP Alumni
VIP Alumni

Hi

There are a few bugs in these 4500x software versions , checking your release though its only got 1 known cdp bug , a quick way to rule it out though is try lldp , if lldp is working there may be an issue with the cdp feature on the current 4500x software version

CSCuu25770

IOSd crash triggered by certain CDP packet

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/release/note/OL_32142-01.html

Thanks Mark,

The 4500X is happily switching, no crashes, so it doesn't look like CSCuu25770.

I've enabled lldp, and I'm seeing the same behaviour as for CDP: the core 4500X is visible on the 3850s, but the 3850s aren't visible on the 4500X.

Unfortunately the switches are in production, so trying different versions of IOS will require out-of-hours downtime to be scheduled.

Daniel

Yes that's a pity even lldp doesn't work , cdp was broken in earlier releases as well but lldp still worked as a temporary resolve

https://supportforums.cisco.com/discussion/12947526/4500x-vss-no-cdp-neighbors

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