HSRP Virtual MAC Format

[chlee_softbank]

Hi, everyone.

Recently customers insisted that ping failed (for a while) from their own NMS system to host. And Cisco HSRP are working in the middle of their cloud.

Question) 00:00:0c:9f:f7:6e can be HSRP Virtual MAC?? In my understanding, 0000.0c07.ac0a is HSRP Virtual MAC though.

0000.0c (Vendor Code)

07.ac    (Well-known HSRP Code)

0a         (HSRP Group number 10 in hex)

Information related to HSRP(version2, IPv4 group 1902) by capture.

[1] Active IP : 33.136.2.2 (Cisco_9f:f6:62). Cisco=54:75:d0

[2] Standby IP : 33.136.2.3 (Cisco_ae:27:99) Cisco=54:75:d0

[3] Virtual IP : 33.136.2.1 (All hosts' Gateway IP address)

By capture, host received ping request and can't response for a while and keep responding.

During no responding, there are ARP reply between Cisco and host.

-->> Cisco_9f:f7:6e (source)  Somevend_b3:83:00 ARP  33.136.2.1 at 00:00:0c:9f:f7:6e

-->> Cisco_9f:f7:6e = 00:00:0c:9f:f7:6e.

Small Question) Ping from NMS and ping from local server have different source. Is it possible?

Ping from NMS has source Active(HSRP) 54:75:d0:9f:f6:62

Ping from local server has source Standby(HSRP)  54:75:d0:ae:27:99

Many Thanks!!!

Jeff D. LEE

[David Lucas]

Hello!

What kind of devices are these and what is the version of code they are running?

Dave

[SelamsewAmha]

problem solved!

Thank you

the problem was there was a VACL on one of the distribution switches which was there for long before we introduced these new set of VLAN ranges.

vlan access-map PTS-STUDENT VLan-list 14-15

as soon as i removed this, the hsrp communication resumed

thank you again all!

[Peter Paluch · Accepted solution]

Hello,

Question) 00:00:0c:9f:f7:6e can be HSRP Virtual MAC??

Yes. The HSRP Version 2 uses a new MAC address range 0000.0C9F.F000 to 0000.0C9F.FFFF. Your MAC address corresponds to the standby group number 0x76e = 1902. For more information, see:

http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gthsrpv2.pdf

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_q_and_a_item09186a00800a9679.shtml#q34

http://www.cisco.com/en/US/docs/ios-xml/ios/ipapp_fhrp/configuration/15-mt/fhp-hsrp.html#GUID-B0BBD2FE-41B4-4339-BF89-CD394685F7FB

In my understanding, 0000.0c07.ac0a is HSRP Virtual MAC though

This is true for HSRP Version 1. Version 2 uses a different MAC address prefix as noted above.

Small Question) Ping from NMS and ping from local server have different source. Is it possible?
Ping from NMS has source Active(HSRP) 54:75:d0:9f:f6:62
Ping from local server has source Standby(HSRP)  54:75:d0:ae:27:99

I apologize, I do not understand this. Neither of mentioned MAC addresses corresponds to HSRP MAC address. Perhaps you could clarify this with a picture of your topology.

Best regards,

Peter

[chlee_softbank]

Hi, Peter

Really thanks! It helps alot.

Jeff