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Author Topic: ARP issue with a stack of 4550T-PWR in SW5.6.1  (Read 2230 times)

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Offline Dorian

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ARP issue with a stack of 4550T-PWR in SW5.6.1
« on: August 21, 2014, 05:39:34 AM »
Hello, I have a strange behavior on one of my 4500T-PWR stack. It's a stack of 6 units running FW 5.3.0.3 and SW 5.6.1.

My stack is the core element of my agency. There is 4 vlan with routing between them. The stack is performing all routing operation. I made my test from a computer in the vlan 200. The test is quite simple I tried to ping the gateway (ie the stack) and observed a very weird ARP exchange between my computer and my stack. I made the test with another computer => same result.

my computer is in 10.128.199.220 my stack is in 10.128.196.1 (netmask is 255.255.252.0)
the exchange is the following:
- ARP request from my computer to ask who as 10.128.196.1
Address Resolution Protocol (request)
    Hardware type: Ethernet (1)
    Protocol type: IP (0x0800)
    Hardware size: 6
    Protocol size: 4
    Opcode: request (1)
    Sender MAC address: Hewlett-_97:9f:d7 (1c:c1:de:97:9f:d7)
    Sender IP address: 10.128.199.220 (10.128.199.220)
    Target MAC address: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Target IP address: 10.128.196.1 (10.128.196.1)
- ARP answer from the stack
Address Resolution Protocol (reply)
    Hardware type: Ethernet (1)
    Protocol type: IP (0x0800)
    Hardware size: 6
    Protocol size: 4
    Opcode: reply (2)
    Sender MAC address: Avaya_8b:c4:41 (70:52:c5:8b:c4:41)
    Sender IP address: 10.128.196.1 (10.128.196.1)
    Target MAC address: Hewlett-_97:9f:d7 (1c:c1:de:97:9f:d7)
    Target IP address: 10.128.199.220 (10.128.199.220)
First ping sent from my computer to the stack
Ethernet II, Src: Hewlett-_97:9f:d7 (1c:c1:de:97:9f:d7), Dst: Avaya_8b:c4:41 (70:52:c5:8b:c4:41)
Internet Protocol Version 4, Src: 10.128.199.220 (10.128.199.220), Dst: 10.128.196.1 (10.128.196.1)
Internet Control Message Protocol
    Type: 8 (Echo (ping) request)
    Code: 0
    Checksum: 0x4cab [correct]
    Identifier (BE): 1 (0x0001)
    Identifier (LE): 256 (0x0100)
    Sequence number (BE): 176 (0x00b0)
    Sequence number (LE): 45056 (0xb000)
    Data (32 bytes)

Until then everything is fine and works as expected. But after that, the weird behavior begins. First I have a new ARP request from my stack asking for the MAC address of my computer. It's strange because the previous packet should have updated correctly the ARP table of the stack
- ARP request from the stack
Address Resolution Protocol (request)
    Hardware type: Ethernet (1)
    Protocol type: IP (0x0800)
    Hardware size: 6
    Protocol size: 4
    Opcode: request (1)
    Sender MAC address: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Sender IP address: 10.128.196.1 (10.128.196.1)
    Target MAC address: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Target IP address: 10.128.199.220 (10.128.199.220)

In this request we can see that the Sender MAC address field of the request is filled with 0000. Which is not expected.

my computer updates its ARP table with this new strange MAC address and sends its answer
Ethernet II, Src: Hewlett-_97:9f:d7 (1c:c1:de:97:9f:d7), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Address Resolution Protocol (reply)
    Hardware type: Ethernet (1)
    Protocol type: IP (0x0800)
    Hardware size: 6
    Protocol size: 4
    Opcode: reply (2)
    Sender MAC address: Hewlett-_97:9f:d7 (1c:c1:de:97:9f:d7)
    Sender IP address: 10.128.199.220 (10.128.199.220)
    Target MAC address: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Target IP address: 10.128.196.1 (10.128.196.1)

and it sends another ping request with the updated mac dest mac address 00:00:00:00:00:00
Ethernet II, Src: Hewlett-_97:9f:d7 (1c:c1:de:97:9f:d7), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 10.128.199.220 (10.128.199.220), Dst: 10.128.196.1 (10.128.196.1)
Internet Control Message Protocol
    Type: 8 (Echo (ping) request)
    Code: 0
    Checksum: 0x4caa [correct]
    Identifier (BE): 1 (0x0001)
    Identifier (LE): 256 (0x0100)
    Sequence number (BE): 177 (0x00b1)
    Sequence number (LE): 45312 (0xb100)
    Data (32 bytes)

All other devices on the network segment have updated although their ARP table with this wrong mac address => everything is blocked for a few seconds until all devices updated their arp again...

Is this a known bug/normal behavior ?


Offline TankII

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  • Posts: 556
Re: ARP issue with a stack of 4550T-PWR in SW5.6.1
« Reply #1 on: August 28, 2014, 02:11:18 PM »
Are your bridge timers at default of 300 or did you change them to 21601?

TankII

Offline Michael McNamara

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  • Posts: 3842
    • michaelfmcnamara
    • Michael McNamara
Re: ARP issue with a stack of 4550T-PWR in SW5.6.1
« Reply #2 on: August 29, 2014, 08:16:01 AM »
Looks to me like you've definitely stumbled upon a software bug... I would open a support ticket with Avaya if you have a support contract.
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