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Cat6500 IOS: cdp neighbors on trunk without vlan 1

The question is: how can a Cat6506-IOS send through CDP protocol any of its configured IP addresses instead of its SPV loopback address?

The scenario is: a Cat6506 SPV2-MSFC2 with IOS version 12.2(17d)SXB10 connected through a WS-X6516A-GBIC interface to a Cisco 7200 equipped with C7200-I/O-GE+E, NPE400 and IOS version 12.2(27).

The information received by the 7200 router through the CDP protocol is the following:

Device ID: sw6506-1.mycompany.lan

Entry address(es):

IP address: 127.0.0.12

Platform: Cisco WS-C6506, Capabilities: Router Switch

[…]

The information received by the 6506 through the CDP protocol is the following:

Device ID: router7200.mycompany.lan

Entry address(es):

IP address: 172.16.0.31

Platform: Cisco 7204VXR, Capabilities: Router

[…]

Note: the IP address 172.16.0.31 is configured on the router as IP interface Looback 0 address.

The link is a trunk 802.1q, the 6506 interface is in switching mode and its detail is following:

[…]

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: On

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

[…]

Trunking VLANs Enabled: 3,10,21,541,860,890,891

[…]

Every VLAN configured on trunk has its corresponding Interface Vlan on the 6506 and a subinterface on the 7200 with their corresponding IP addresses.

Best regards.

  • Other Network Infrastructure Subjects
2 REPLIES

Re: Cat6500 IOS: cdp neighbors on trunk without vlan 1

Hi Friend,

CDP carry the ip information which is used as a management purpose on a device and the loopback address remains up till the time the device is up no matter even if any interface goes down loopback interface will stay up.

AFAIK you cannot change the ip information carried by CDP protocol.

Regards,

Ankur

New Member

Re: Cat6500 IOS: cdp neighbors on trunk without vlan 1

Thanks Ankur,

the 6500 CDP problem is regarding which IP is elected by the IOS as "management address" to distribute via CDP: I think that should the first Loopback interface address to be elected, and this is the behavior in the old 12.2(17d)SXB1 IOS version, presently deferred.

I understand that I cannot modify the CDP behavior, but CDP is for "human" management and 127.0.0.12 is a "machine" management address, so it is useless and is the same for every 6500 in the same state. Also “Topology services” of CiscoWorks has a faulty behavior for the same reason.

I have supposed that the odd behavior is the result of the Vlan1 removal, but the 6500 installed in the LAN have a mission critical role and I cannot experiment anything on them, so I ask to the forum a possible workaround.

Sincerely. Paolo.

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