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HSRP mac address

Hi,

Does someone know  HSRP 's mac address used when we have two physicals routers connected to a LAN ?

i.e: fa0/0 of router 1 is connected to SW1

      fa0/0 of router 2 is connected to SW1

when we ping the logical HSRP addess we will se witch address mac in the arp and mac-address-table ? router1'mac or router2's mac or another one ?

Kind regards,

2 ACCEPTED SOLUTIONS

Accepted Solutions
New Member

Re: HSRP mac address

The MAC address 00-00-0c-07-ac-xx is reserved for HSRP, and xx is the HSRP group number in hexadecimal.  so make sure you're comfortable with hex conversions. The group number is 5, which is expressed as 05 with a two-bit hex character. If the group number had been 17, we'd see 11 at the end of the MAC address - one unit of 16, one unit of 1.

Regards.

Thinakaraj.M

Re: HSRP mac address

thank you ganeshh, but what is the argument to change to strainght cable ? i will gain in performance ? i'm connected in half-duplex but with 100 MB.

to switch to full duplex it will add something ?

Thanks.

Half-duplex is used to describe communication where only one side can talk at a time. Once one side has finished transmitting its data, the other side can respond. Only one node can talk at a time. If both try to talk at the same time, a collision will occur on the network.

As you can understand, this method of communication is not very efficient and requires more time to send/receive larger amounts of data.

On the other hand, full-duplex is used to describe communication where both sides are able to send and receive data at the same time. In these cases, there is no danger of a collision and therefore the transfer of data is completed much faster.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

8 REPLIES
New Member

Re: HSRP mac address

The MAC address 00-00-0c-07-ac-xx is reserved for HSRP, and xx is the HSRP group number in hexadecimal.  so make sure you're comfortable with hex conversions. The group number is 5, which is expressed as 05 with a two-bit hex character. If the group number had been 17, we'd see 11 at the end of the MAC address - one unit of 16, one unit of 1.

Regards.

Thinakaraj.M

New Member

Re: HSRP mac address

Thanks for your reply. In this case, the mac used is neither router1's mac nor router2's mac ?

it's a special value , is it right ?

I have also another question if you can help : my two routers are connected two the LAN using crossover cables.

it's this a good solution as i see that interface are connected in half-duplex ? routers are using their high performance with crossover cables ?

should i change to straight trough cables in order to have the full duplex ?

Thanks,

AA

Re: HSRP mac address

Thanks for your reply. In this case, the mac used is neither router1's mac nor router2's mac ?

it's a special value , is it right ?

I have also another question if you can help : my two routers are connected two the LAN using crossover cables.

it's this a good solution as i see that interface are connected in half-duplex ? routers are using their high performance with crossover cables ?

should i change to straight trough cables in order to have the full duplex ?

Thanks,

AA

Mac address  00-00-0c-07-ac-xx used by HSRP where xx is the  group number in hexadecimal.To have better results you should have full duplex configuration from router to switch,You can use staright cable is router are connected with switch with interafce configuation as full and speed 1000Mbps.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

New Member

Re: HSRP mac address

thank you ganeshh, but what is the argument to change to strainght cable ? i will gain in performance ? i'm connected in half-duplex but with 100 MB.

to switch to full duplex it will add something ?

Thanks.

Re: HSRP mac address

thank you ganeshh, but what is the argument to change to strainght cable ? i will gain in performance ? i'm connected in half-duplex but with 100 MB.

to switch to full duplex it will add something ?

Thanks.

Half-duplex is used to describe communication where only one side can talk at a time. Once one side has finished transmitting its data, the other side can respond. Only one node can talk at a time. If both try to talk at the same time, a collision will occur on the network.

As you can understand, this method of communication is not very efficient and requires more time to send/receive larger amounts of data.

On the other hand, full-duplex is used to describe communication where both sides are able to send and receive data at the same time. In these cases, there is no danger of a collision and therefore the transfer of data is completed much faster.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

Re: HSRP mac address

Hi,

Does someone know  HSRP 's mac address used when we have two physicals routers connected to a LAN ?

i.e: fa0/0 of router 1 is connected to SW1

      fa0/0 of router 2 is connected to SW1

when we ping the logical HSRP addess we will se witch address mac in the arp and mac-address-table ? router1'mac or router2's mac or another one ?

Kind regards,

Hi,

When a router/switch becomes active, it broadcasts a gratuitous ARP packet with the HSRP virtual MAC address to the affected LAN segment. If the segment uses an Ethernet switch, this allows the switch to change the location of the virtual MAC address so that packets go to the new router instead of the one that is no longer active.

when you issue show standby command on both active and passive device who can the virtual mac is associted with the active router.As told The MAC address 00-00-0c-07-ac-xx is reserved for HSRP, and xx is the  group number in hexadecimal.

On rare occasions, you may have to change the MAC address assigned to  the virtual router. This is done with the standby mac-address command.

London(config-if)#standby 5 mac-address 0000.1111.2222

Hope to help !!

Ganesh.H

Remember to rate the helpful post

Re: HSRP mac address

Hi,

You should see the active HSRP mac-address on the Arp table. although there is avirtual mac created but this mac is actually created for local communication between HSRP groups. The last 1 byte of the virtual mac address of the HSRP determines the group number in hex.

However, as I mentioned, you will always see the mac-address of the active HSRP when you ping the virtual HSRP address, and the host arp request will be directed to it.

HTH

Mohamed

New Member

Re: HSRP mac address

hi

i would like to add something...

in the HSRP the active mac is the same allways.

only the active routere or switch is going to change bec. network fail.

to know the active interface or active rotuter... just tel net the HSRP ip ...

you will find the device which is acitve.

Regards,

Thinakaraj.M

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