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Cisco Bug: CSCvj02540 - SG300-10MPP - The DHCP-Server offers default-gateway IP from different vlan.

Last Modified

Aug 15, 2018

Products (1)

  • Cisco Small Business 500 Series Stackable Managed Switches

Known Affected Releases

1.4.8.6

Description (partial)

Symptom:
Inspected on: Cisco SG300-10MPP (VID: V03, FW: 1.4.8.6)
Overview:

* L3-Mode
* Acts as DHCP-Server on different VLANs
* Clients are connected to different VLANs via WLAN-APs on trunk ports
Problem:
The DHCP-Server on vlan12 offers a DHCP-lease from correct pool, but with a default-gateway IP from vlan11.
This is no bug on the client, since the wrong default-gateway information in the DHCP-Offer can be seen in a network trace.
Trimmed configuration:
interface vlan 11
ip address 172.17.0.1 255.255.248.0
interface vlan 12
ip address 172.17.8.1 255.255.248.0
exit
ip dhcp pool network dhcp-pool_vlan11
address low 172.17.0.32 high 172.17.7.254 255.255.248.0 default-router 172.17.0.1 exit ip dhcp pool network dhcp-pool_vlan12 address low 172.17.8.8 high 172.17.15.254 255.255.248.0 default-router 172.17.8.1

Conditions:
seen with having trunk connection to AP with multiple SSID where users easily move between SSID
2 customers reported but not able to replicate on demand

1. The wireshark-trace file has a timestamp of march 7, 2018 (2018-03-07, yyyy-mm-dd).
2. configuration backup archive for the switch, the last configuration backup (2017-10-31) has the following lines on the beginning:
	config-file-header
	sw01
	v1.4.8.6 / R800_NIK_1_4_202_008
	CLI v1.0
	set system mode router
=> according to this facts, 100% sure, that the firmware-version was 1.4.8.6 at the time of the bug occuring.

In the full trace, one can see the ARP requests from two other devices (two samsung android smartphones). Since they ask for the MAC of the same (wrong) default-gateway, one can see, that not only one windows system was affected by the bug.

Regarding Hardware-Version of the switch: SG300-10MPP-K9 V03, MAC: a0:f8:49:5c:d1:5b, S/N: PSZ21211CX9.
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