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New Member

Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Hi all

I have a hp 8000m connected to a hp 2524. This does not support vlan and two mac addresses. We have a cisco 2811 router which is connected to our cisco 2950. The 2950 is uplinked into the hp. The router has an admin network and a curric network (two interfaces/cables).

My question is can we change the mac address of the router plugged into the 2950 so then the HP procurve will be happy as their are two different mac addresses for the gateway. I dont have access to the router (managed upstream) but can access the cisco 2950 to do changes.

I tried playing with the arp table and adding statics but did not have any luck. I even tried clearing the arp table many times and testing arp -a no luck.

HELP! Please

Thanks

Jon

10 REPLIES
Silver

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Hello Jon,

I am not shure how you could have a duplicate IP address of both a Cisco router and a HP 8000m.

The OUI (first 24 bits) part from Cisco and HP assigned addresses are unique. Can you give an example, and if possible create a simple diagram of your network.

--Leon

New Member

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Thanks for your help.

I have attached a visio 2003 network diagram.

Well the admin interface of the 2811 router has seperate IP's but the same MAC. This is because their is one module with 4 ports on the cisco 2811.

The hp 8000m and 2524 does not support two mac addresses the same as is confused only in VLAN so it sends packets to one mac address then changes to the other, this causes problems with the two clients connected on the admin vlan (red).

I am wondering if the cisco switch 2950 can somehow fix this situation by changing mac address of the router or arp table.

I cant manage the 2811 router as it is managed upstream, they are looking into this but I dont know how long it will take them to find a solution.

HP recommend vlan'ing the 8000m into the cisco 2811 with one cable so therefore there are not two mac addresses but this is not possible as it is not a "standard" setup with our providers.

Thanks

Silver

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Jon,

The Cisco 2811 has two fixed LAN ports. If you have a 4-port FastEthernet module each and every port (should) have a unique mac-address.

In case the destination address is on an other subnet you see for both router interface as the destination the SAME Layer 2 address in the ARP table. Please not that the ARP table is not the same as the MAC address table.

Please gather information from the MAC address table by issuing "show mac-address-table interface Fa0/N where "N" represents an interesting port.

When you ping both admin and curric interfaces from the C2950 issue "show arp" can you see differences from information gathered from the MAC address-table?

Thank you.

--Leon

New Member

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Thanks again

The cisco 2811 is using the 4 port module. You are probably right about the unique mac address but in the arp table it is appearing as the same.

I have tried int fastethernet 0/11 and mac-address to change mac address but this still does not seem to alter it when it is uplinked into the hp 8000m.

e.g

FastEthernet0/11 is up, line protocol is up (connected)

Hardware is Fast Ethernet, address is 0015.627f.3961 (bia 0014.1ccc.9f8b)

I changed it from 60 to 61 but still is shown on xp client:

On client:

Internet Address Physical Address Type

10.136.24.1 00-15-62-7f-39-60 dynamic

From curric acls are set on the 2811 router by our provider. curric goes out of curric interface of router and admin can talk to curric lan. curric cannot talk to admin. admin is on a different subnet to curric.

When I ping .1 from curric which is the router I find the mac address. When I use an admin workstation and do the same ping the admin ip .1 the arp is the same mac address.

The c2950 is only curric network. the vlan is only set in the hp 8000m to 2524 hp.

Silver

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Changing the MAC address of your switchport would not help as the devices share the same subnet. The frame from the router is received "unchanged".

Please re-read my previous post as I tried to explain that hosts behind the router are visible in the ARP table with the MAC address of the router associated to it. This is normal behaviour as the router is a boundary for Layer 2 information.

--Leon

New Member

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Thanks Leon.

as you said ->Please gather information from the MAC address table by issuing "show mac-address-table interface Fa0/N where "N" represents an interesting port.

This is what I see:

Mac Address Table

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

Vlan Mac Address Type Ports

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

1 0015.627f.3960 DYNAMIC Fa0/11

1 0015.6354.86ea DYNAMIC Fa0/11

Total Mac Addresses for this criterion: 2

-> When you ping both admin and curric interfaces from the C2950 issue "show arp" can you see differences from information gathered from the MAC address-table?

The c2950 does not see the red admin as it is not setup with vlan. It is a curric switch with the 2811 router into port 11.

This is show arp:

Protocol Address Age (min) Hardware Addr Type Interface

Internet 10.136.24.8 - 0014.1ccc.9f80 ARPA Vlan1

Internet 10.136.24.1 - 0001.627f.3960 ARPA

Internet 10.136.24.61 3 0011.5b95.a2ae ARPA Vlan1

Do you want me to setup vlan from the hp8000m to the c2950 then I could ping both admin and curric interfaces from vlan ?

Thanks for your help it is much appreciated

Silver

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Jon,

I see two paths to the 2811 from the perspective of the HP ProCurve 8000m. One through the Cisco 2950 and one through the 3Com 4228G.

The 3Com resides on another IP subnet. Can you reach the admin interface of the 2811 from the 3Com switch? If so your best bet is to create a VLAN interface on the 8000m and place it into the same IP subnet as the 3Com.

HP ProCurve

vlan 109

ip address 161.x.x.x 255.255.x.x

int A1

untag 109

HTH

--Leon

* Please rate posts.

New Member

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

-> I see two paths to the 2811 from the perspective of the HP ProCurve 8000m. One through the Cisco 2950 and one through the 3Com 4228G.

This is correct.

-> The 3Com resides on another IP subnet. Can you reach the admin interface of the 2811 from the 3Com switch? If so your best bet is to create a VLAN interface on the 8000m and place it into the same IP subnet as the 3Com.

Yes 3com is plugged into admin interface of 2811 and c2950 is plugged into curric interface of 2811 router.

The procurve 8000m is already setup with blue (curric) and red (admin) vlan.

VLAN | IP Config IP Address Subnet Mask Gateway

------------ + ---------- --------------- --------------- ---------------

DEFAULT_VLAN | Disabled

RED | Manual 10.161.154.3 255.255.255.0 10.161.154.1

BLUE | Manual 10.136.24.3 255.255.252.0 10.136.24.1

Name 802.1Q VLAN ID

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

DEFAULT_VLAN 1

BLUE 111

RED 222

port a8 (plugged into 3com) red: untag blue: no

everything else red: no blue: untag

i1 j1 j2 j3 fibre ports red: tagged blue: untag

Problem is hp 8000m is confused with two mac addresses. it switches back and forth, one minute giving the admin vlan full access through router then changes and does not let it through. HP procurve 8000m does not support vlan and two mac address scenario.

001562-7f3960 A8

001563-5486e9 A8

001562-7f3960 D8

Here is more: not sure if this makes sense:

port a8 -> vlan admin to 3com switch from hp 8000m

MAC Address

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

000c76-8c3ea6

000c76-8c3ead

000e6a-558229

001563-5486e9 <- router??

00c09f-37dfa4

00c0ee-201dcf

00c0f0-3c9247

--

port d8 -> to c2950 from hp 8000m

MAC Address

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

000347-3273d1

000ae4-0bad93

000bbe-961574

00115b-95a2ae

001319-05dfa5

001319-05dfba

001319-05e025

001319-05e051

00141c-cc9f80

00141c-cc9f98

001563-5486ea <- router?

-

port d8 changes after a minute to this:

MAC Address

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

000347-3273d1

000ae4-0bad93

00115b-95a2ae

001319-05dfa5

001319-05dfba

001319-05e025

001319-05e051

00141c-cc9f80

00141c-cc9f98

001562-7f3960 <- router?

009027-0daeaa

I recv this from my provider: He telneted into the router 2811

FastEthernet0/0/0 is up, line protocol is up

Hardware is Fast Ethernet, address is 0015.6354.86e9 (bia 0015.6354.86e9)

Description: Admin LAN.

sh int f0/0/1

FastEthernet0/0/1 is up, line protocol is up

Hardware is Fast Ethernet, address is 0015.6354.86ea (bia 0015.6354.86ea)

Description: Curriculum LAN.

that explains the 86ea curric and 86e9 admin

Am I reading your post wrong? Does the above help?

Silver

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Hi Jon,

To resolve this issue you need to re-design your network. The current setup fails to meet your reachability requirements. The redundant paths between HP ProCurve 8000 and Cisco Catalyst 2950 can cause loops and upredicatable forwarding behaviour.

All the components have are capable of segmenting IP subnets by using VLANs.

I recommend that you setup the HP ProCurve 8000 as your default router. This will give you control over the routing of traffic between Admin and Curriculum VLANs.

From the HP ProCurve 8000 switch you can set a default route for traffic to the Internet. The Admin network is reachable because it is directly connected to the HP ProCurve 8000 switch.

I hope this helps you resolving your problem.

Best regards,

Leon

New Member

Re: Cisco 2950 HP 8000m and 2524 vlan duplicate mac address

Unfortunately, I think I will need to buy new switches or fibre converters a create a seperate fibre connection and switch to seperate the admin lan and not use the vlan.

As long as the hp 8000 or 2524 uses vlan and it see's 2 mac address gateway's it is not going to work.

Do you mean to set the two admin workstations to the gateway of the procurve? I think the hp's will still have problems as said above?

You have been a great help though and I have learnt a bit more about cisco 2950's in the meantime.

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