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DHCP Offer is unicasted to the old MAC on the ARP cache

Hi,

DHCP Offer is unicasted to the old MAC on the ARP cache. This behaviour is happening as soon as we are connecting 2 or more IP phones in the network with DHCP settings. Avaya support persons have verified all configurations are intact(option 176 etc).

I have checked sniffers for this & it shows that Phone-1 boots in following sequence

1. DHCP Discover in Data Vlan

2. DHCP Offer (IP from Data Vlan 172.16.1.1)

3. ARP Verification

4. DHCP Request (for Data Vlan IP address)

5. DHCP ACK

6. ARP Verification

7. G-ARP.

8. Phone reloads again to get IP in Voice Vlan

9. DHCP Discover in Voice Vlan

10. DHCP Offer (IP from Voice Vlan)

11. ARP Verification

12. DHCP Request (for Voice Vlan IP address)

13. DHCP ACK

14. ARP Verification

15. G-ARP.

When Phone-2 boots

1. DHCP Discover in Data Vlan

2. DHCP Offer (IP from Data Vlan 172.16.1.1 b/c this IP was released by phone-1)

At this stage sniffers clearly show that DHCP-Offer goes to Phone-1's MAC address(172.16.1.1----Phone-1 MAC)....When we see show ip arp on router it shows 172.16.1.1 mapped to phone-1's MAC, after clear this arp entry phone-2 is reloaded & it registers properly using sequence(1-15).

I am wondering why this IP-MAC entry is not getting out when Phone-1 releases the IP to DHCP. It seems to me a bug which might be hitting.

I have tested DHCP stuff by connecting PC in both Data & Voice(by changing it to access vlan) Vlans they are properly getting IP addresses from DHCP, it seems that DHCP relay is also working properly.

Would appreciate if someone is having insight of this.....

Router IOS is c2800nm-advsecurityk9-mz.124-22.T.bin

Regards,

Akhtar

3 REPLIES
Hall of Fame Super Silver

Re: DHCP Offer is unicasted to the old MAC on the ARP cache

Hello Aktar,

I've found an existing bug with same description

CSCsu67864 Bug Details Bug #35 of 47 | < Previous | Next >

DHCP Offer is unicasted to the old MAC on the ARP cache

your IOS image is among affected versions:

>>>12.4(22)T                
12.4(22)T1                
12.4(22)T2                
12.4(22)T3                
12.4(22)T4 

you need to upgrade to 12.4(24)T

Hope to help

Giuseppe

New Member

Re: DHCP Offer is unicasted to the old MAC on the ARP cache

Thanks Giuseppe. Will upgrade the image & check the behaviour.

Regards,

Akhtar

New Member

Re: DHCP Offer is unicasted to the old MAC on the ARP cache

got rid of the bug after upgrade. Thanks

Regards,

Akhtar

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