VTP / HSRP Question

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Apr 27th, 2007
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Hi


We're planning to upgrade our network infrastructure to this design.


R1 is connected to r2 and R3

R4 is connected to R2 and R4 (wen applying this post the connection between R2 and R4 is not displayed correctly)


R1 ---- R2

| |

| |

R3 ---- R4


Router R1 and R3 are going to be configured in VTP domain 1, Router R2 and R4 is going to be in VTP Domain 2.


R1 and R3 configured OSPF area 0

R2 and R4 OSPF area 1


R1 and R3 are going to be redundant via HSRP, R2 and R4 also via HSRP.


Assume we are going to create the same vlan id in bot vtp domains, is it possible to create and HSRP group where the group members are R1 and R2 for a vlan configured with the same id in different vtp domains?


If no, how can we solve this...


According to me there will be no problem only if VTP is using internal numbers ( or internal ids) for its vlan instead of the configured ids)


Thanks


Jorg

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royalblues Fri, 04/27/2007 - 03:44
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Jorg,


As long as your VTP domain is seperate it should not matter.


One thing i would take care is the HSRP standby group for the VLANs. The Default HSRP MAC-Address will be 00-00-0c-07-ac-xx where XX will be the standby group number. If the standby groups are same then you end up with the same HSRP MAC-ID for both the groups which might create problems.


HTH, rate if it does

Narayan

jorgRamakers Fri, 04/27/2007 - 03:59
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Hi thanks for the reply,


Can we also create an hsrp group for, for examle vlan 10 which is on both sides. So both vlan can use the same virtual ip addresses.


r1 --- r2

| |

r3 --- r4

^ ^ vlan 10

Vlan 10


So the hsrp is going over the routed link between r3 and r4?


Best regards


Jorg Ramakers

royalblues Fri, 04/27/2007 - 04:09
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Jorg,

That shouldn't be a problem.


I didn't read the post properly first time and probably overlooked the L3 links in between. No problems in the setup with OSPF running between them.


HTH, rate if it does

Narayan

jorgRamakers Fri, 04/27/2007 - 04:17
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Thanks,


Is i thought hsrp is L3 so routing will be no problem.


You just told that the last digits of the hsrp mac-address is the vlan number, on my routers all mac-addresses looks the same, all 07.ac.00 on the end.



royalblues Fri, 04/27/2007 - 04:26
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Jorg,


HSRP is considered a Layer 2 gateway redundnacy protocol.


The HSRP Mac-address does have the following part as reserved 00-00-0c-07-ac-XX. The XX is the standby group (in Hex)you define on the configurations.


http://www.cisco.com/warp/public/cc/pd/iosw/iore/prodlit/768_pb.htm#wp15862


http://www.mcmcse.com/cisco/guides/hsrp_mac_address.shtml


HTH, rate if it does

Narayan

jorgRamakers Fri, 04/27/2007 - 05:36
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Ah,


I just saw the reason why it is showing the same mac-address. They configured the hsrp on the vlan interface and didn't specify the group id, so every hsrp address is using the same mac-address.


I don't think this can be a problem as hsrp is configured on vlan interface.

Do you see any problems dealing with this config/misconfig?

royalblues Fri, 04/27/2007 - 06:31
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it should not but it is always advisable to have vlans with different standby groups.


I had run into a problem once and i had changed the standby group number

you will generally a message

FastEthernet0/0 Grp 1 active routers virtual IP address x.x.x.x is different to the locally configured address y.y.y.y


The messages explain the new virtual IP address is not in the same subnet with the real IP addresses. This problem occurs because your stand by group is same with other HSRP group.


HTH, rate if it does

Narayan

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