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Can I configure a switch to use a specific SVI or does the switch chooses it automatically?

Jacob Gwangwa
Beginner
Beginner

I have a 6509 VSS. This switch is configured with a Management VLAN called SWITCH_MANAGEMENT with this IP address 192.168.25.250 which i expect it to display in all neighbour switches when i do show cdp neighbour details.

VLAN Name                             Status    Ports

---- -------------------------------- --------- -------------------------------

5    SWITCH_MANAGEMENT                active    Gi1/2/26, Gi1/2/27, Gi1/5/1, Po21, Po22, Po24, Po25, Po26 - not complete.

However when i'm on a neighbour switch and do show cdp neighbour details it displays the below results which is not what i'm expecting;

Entry address(es):

IP address: 172.16.2.2

Platform: cisco WS-C6509-V-E,  Capabilities: Router Switch IGMP

Interface: GigabitEthernet2/3,  Port ID (outgoing port): GigabitEthernet2/2/2

Holdtime : 176 sec

Why cant this neighbour switch show this IP 192.168.25.250 as its purely configured for management? Instead it shows the IP of VLAN 2 see below config:

This IP 172.16.2.2 is configure for SVI VLAN 2;

interface Vlan2
description SERVER_VLAN_2
ip address 172.16.2.2 255.255.255.0

Any help in understanding this would be appreciated.

Thanks,

Jacob Gwangwa

1 Accepted Solution

Accepted Solutions

Edison Ortiz
Hall of Fame Mentor Hall of Fame Mentor
Hall of Fame Mentor

By default, CDP will use the IP address of the first available interface with an IP.

You can use the 'cdp source-interface' command to force which IP address is presented to the neighbors.

View solution in original post

9 Replies 9

Edison Ortiz
Hall of Fame Mentor Hall of Fame Mentor
Hall of Fame Mentor

By default, CDP will use the IP address of the first available interface with an IP.

You can use the 'cdp source-interface' command to force which IP address is presented to the neighbors.

Edison,

Do you have reference to this command?

I can't seem to find this command in IOS 15 running on a stack of 3750s.

There is hodltime, advertise-v2, timers, etc... but no source command.

Reza

Not supported under that platform. Only under 7600, 6500 and Cisco Routers.

Ok, thanks

Ok, I must retract my previous statement - my apologies.

This command is not available with the 6500 platform hence no use to the original poster.

The documentation I read was wrong.

I tried the command on a lab box and it was not available.

It is available on IOS routers, though.

This new documentation reflects the supported platforms:

http://www.cisco.com/en/US/docs/ios-xml/ios/cdp/command/cdp-cr-a1.html#GUID-BF50AA69-6AFE-4153-B2DE-1B9843B5A4B9

I was just about to go and run this command on a 6500.

Thanks for the update.

Thanks to all. You've really helped me figure out what I need to do. Probably I'll change the VLAN ID to be the least one for instance VLAN 5 (192.168.25.250-preferred) to VLAN 2 (172.16.2.2 - Not Prefered) & test the results.

This will be done when I return from my leave next January 20, 2013.

Thanks once again!

Hi Jacob,

If the answers and discussion was helpful to you, please rate and mark it as answered, so others can benefit from it.

Thanks

Hi Reza

The correct answer is this one by Edison where he said "

By default, CDP will use the IP address of the first available interface with an IP.

You can use the 'cdp source-interface' command to force which IP address is presented to the neighbors."

I did a simple test since i'm home using packet tracer specifically just for this matter i've raised.

I configure vlan 2 and gave it an IP 172.16.2.2 and also configured vlan 5 with IP 192.168.25.250 on a 3560 switch. I then connected 5 switches - 2960 x2 and 2950 x 3 and their ports are in auto. I configured 1 to 5 interface ports on the 3560 switch  to be trunk links and connected all 5 switches. On the neighobour switches when i do show cdp neighbour details. i can see the IP of VLAN 2 which is 172.16.2.2. I then deleted the vlan and their IPs and started afresh by giving VLAN 2 IP 192.168.25.250 and VLAN 5 172.16.2.2. I did the show cdp neighbour details on the neighbour switches and the IP  i can see is 192.168.25.250.

So the VLAN id number determines the IP the neighbour is going to use.

Thanks to all for your insightful knowledge.

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