Firmware 1.4.0.88 for SG300-52 appears to break DHCP Relay

[Jonathan Fisher]

My VLANs terminate at my switches, so I use DHCP relay with Option82 to hand out addresses for the VLAN subnet. After upgrading from 1.3.7.18 to 1.4.0.88, DHCP isn't being handed out on my VLANs. Anyone else having this problem?

[V K Moorthy]

Hi,

Boot code need to be upgraded for version  1.4.0.88.Kindly disable the DHCP realy and enable it again.

Kindly check in below URL :  Release notes(Check page no:13)

http://www.cisco.com/c/dam/en/us/td/docs/switches/lan/csbms/sf30x_sg30x/release_notes/R_1_4_RN.pdf

regards

Moorthy

[Jonathan Fisher]

Yes, the boot code was upgraded at the same time the switch firmware was.

I tried:

1. Disable DHCP relay

2. Save

3. Reboot

4. Enable DHCP relay

5. Save

6. Reboot

And it still does not appear to work...

[Aleksandra Dargiel]

Hi Jonathan,

I would recommend you to double check the configuration file. If the DHCP relay is actually present under correct interfaces and if so then another step would be packet capture on this interface to see if the bootp packets are leaving switch.

Regards,

Aleksandra

[Jonathan Fisher]

Right now the switch is running 1.3.7, but:

ip dhcp relay address 192.168.127.129
ip dhcp relay enable
ip dhcp information option

I did pcaps while running 1.4, they show the bootp packets leaving the switch but not entering. It's fairly trivial to reproduce this bug with an SG300 because it has dual firmware. Set to 1.3 as the active image, it works, set to 1.4, it doesn't work. You can flip back and forth between them without changing the config to reproduce the problem.

[Aleksandra Dargiel]

Hi Jonathan,

r u running any type of voice vlan? can you email me your config file via private message?

Aleksandra

[Jonathan Fisher]

No Auto Voice VLAN. 

config sent in pm.

[Aleksandra Dargiel]

You have to do it from your profile, it has change :-)

[Aleksandra Dargiel]

Hi Jonathan,

I have done the test with your configuration file as below:

port gi51 - Windows server 2008

port 1- phone SPA504G

show mac address-table indicates that server is in VLAN 1 while phone in VLAN 124.

I kept bootcode 1.3.5.06 and swap images 1.4.0.88 or 1.3.7.18

Results:

DHCP realy works as expected with both images. I cannot see any problem unless I choose wrong port for server as only 50 and 51 are ip dhcp snooping trusted in your configuration.

 Regards,

Aleksandra

[Jonathan Fisher]

Nuts. I have 4 switches with nearly the exact same configuration and this issue is reproducible on every single one of them.

Is your sg300 in L3 mode and is the DHCP server set to hand out the sg300 as the default gateway to anyone requesting something from vlan 124? 

[Aleksandra Dargiel]

Hi Jonathan,

I have your configuration added manually via CLI. Plugged in DHCP server to port 51 with IP 192.168.127.129/24 and DHCP pool 192.168.124.0/24 which is your VLAN 124 where all the ports are from 1-48. Packet capture shows DHCP Discovery unicast with scr IP 192.168.124.62 dst 192.168.127.129 and DHCP Offer with Client IP 192.168.124.1 and option 3 (router) 192.168.124.62.

all works with no changes in your configuration. To be precise I did not only copy you password settings.

Is your bootcode the same as mine?

Is your server connected to port gi51 or 52?

Aleksandra

[Jonathan Fisher]

Just checked... bootcode is 1.3.5.06, uplink is 51

Any other ideas? Could I try your config on mine?

[Jonathan Fisher]

Not that I think it'll make a difference, but DHCP hands out IP 192.168.124.0/26  with the lowest 192.168.124.1 reserved, and the highest:192.168.124.62 reserved (because that's the sg300's gateway address on VLAN 124)

[Jonathan Fisher]

wait how do I send you a private message? I clicked on your name and I don't see the option anywhere

[tferguso_us · Accepted solution]

I'm just setting up DHCP relay for the first time with my SG 300-28, firmware 1.4.0.88 and noticed that the DHCPDISCOVER promulgated by the relay had the same source and destination port (67), whereas the original DHCPDISCOVER used 67 & 68. Furthermore the 1.3.7.18 firmware doesn't swap these around:

Snippets from Wireshark:

1.4.088 -

Original DHCPDISCOVER from client:

User Datagram Protocol, Src Port: bootpc (68), Dst Port: bootps (67)

Relayed DHCPDISCOVER from SG300:

User Datagram Protocol, Src Port: bootps (67), Dst Port: bootps (67)

That looks a little suspicious to me

1.3.7.18

Original DHCPDISCOVER from client:

User Datagram Protocol, Src Port: bootpc (68), Dst Port: bootps (67)

Relayed DHCPDISCOVER from SG300:

User Datagram Protocol, Src Port: bootpc (68), Dst Port: bootps (67)

I'm not certain that that's your issue (it didn't fix my problem), but thought I'd point it out