2017-10-23 // Experiences with Dell PowerConnect Switches
This blog post is going to be about my recent experiences with Broadcom FASTPATH based Dell PowerConnect M-Series M8024-k and M6348 switches. Especially with their various limitations and – in my opinion – sometimes buggy behaviour.
Recently i was given the opportunity to build a new and central storage and virtualization environment from ground up. This involved a set of hardware systems which – unfortunately – were chosen and purchased previously, before i came on board with the project.
System environment
Specifically those hardware components were:
Multiple Dell PowerEdge M1000e blade chassis
Multiple Dell PowerEdge M-Series blade servers, all equipped with Intel X520 network interfaces for LAN connectivity through fabric A of the blade chassis. Servers with additional central storage requirements were also equipped with QLogic QME/QMD8262 or QLogic/Broadcom BCM57810S iSCSI HBAs for SAN connectivity through fabric B of the blade chassis.
Multiple Dell PowerConnect M8024-k switches in fabric A of the blade chassis forming the LAN network. Those were configured and interconnected as a stack of switches. Each stack of switches had two uplinks, one to each of two carrier grade Cisco border routers. Since the network edge was between those two border routers on the one side and the stack of M8024-k switches on the other side, the switch stack was also used as a layer 3 device and was thus running the default gateways of the local network segments provided to the blade servers.
Multiple Dell PowerConnect M6348 switches, which were connected through aggregated links to the stack of M8024-k switches described above. These switches were exclusively used to provide a LAN connection for external, standalone servers and devices through their external 1 GBit ethernet interfaces. The M6348 switches were located in the slots belonging to fabric C of the blade chassis.
Multiple Dell PowerConnect M8024-k switches in fabric B of the blade chassis forming the SAN network. In contrast to the M8024-k LAN switches, the M8024-k SAN switches were configured and interconnected as individual switches. Since there as no need for outside SAN connectivity, the M8024-k switches in fabric B ran a flat layer 2 network without any layer 3 configuration.
Initially all PowerConnect switches – M8024-k both LAN and SAN and M6348 – ran the firmware version 5.1.8.2.
Multiple Dell EqualLogic PS Series storage systems, providing central block storage capacity for the PowerEdge M-Series blade servers via iSCSI over the SAN mentioned above. Some blade chassis based PS Series models (PS-M4110) were internally connected to the SAN formed by the M8024-k switches in fabric B. Other standalone PS Series models were connected to the same SAN utilizing the external ports of the M8024-k switches.
Multiple Dell EqualLogic FS Series file server appliances, providing central NFS and CIFS storage capacity over the LAN mentioned above. In the back-end those FS Series file server appliances also used the block storage capacity provided by the PS Series storage systems via iSCSI over the SAN mentioned above. Both LAN and SAN connections of the EqualLogic FS Series were made through the external ports of the M8024-k switches.
There were multiple locations with roughly the same setup composed of the hardware components described above. Each location had two daisy-chained Dell PowerEdge M1000e blade chassis systems. The layer 2 LAN and SAN networks stretched over the two blade chassis. The setup at each location is shown in the following schematic:
All in all not an ideal setup. Instead, i would have preferred a pair of capable – both functionality and performance-wise – central top-of-rack switches to which the individual M1000e blade chassis would have been connected. Preferrably a seperate pair for LAN an SAN connectivity. But again, the mentioned components were already preselected and pre-purchased.
During the implementation and later the operational phase several limitations and issues surfaced with regard to the Dell PowerConnect switches and the networks build with them. The following – probably not exhaustive – list of limitations and issues i've encountered is in no particular order with regard to their occurrence or severity.
Limitations
While the Dell PowerConnect switches support VRRP as a redundancy protocol for layer 3 instances, there is only support for VRRP version 2, described in RFC 3768. This limits the use of VRRP to IPv4 only. VRRP version 3 described in RFC 5798, which is needed for the implementation of redundant layer 3 instances for both IPv4 and IPv6, is not supported by Dell PowerConnect switches. Due to this limitation and the need for full IPv6 support in the whole environment, the design decision was made to run the Dell PowerConnect M8024-k switches for the LAN as a stack of switches.
Limited support of routing protocols. There is only support for the routing protocols OSPF and RIP v2 in Dell PowerConnect switches. In this specific setup and triggered by the design decision to run the LAN switches as layer 3 devices, BGP would have been a more suitable routing protocol. Unfortunately there were no plans to implement BGP on the Dell PowerConnect devices.
Limitation in the number of secondary interface addresses. Only one IPv4 secondary address is supported per interface on a layer 3 instance running on the Dell PowerConnect switches. Opposed to e.g. Cisco based layer 3 capable switches this was a limitation that caused, in this particular setup, the need for a lot more (VLAN) interfaces than would otherwise have been necessary.
No IPv6 secondary interface addresses. For IPv6 based layer 3 instances there is no support at all for secondary interface addresses. Although this might be a fundamental rather than product specific limitation.
For layer 3 instances in general there is no support for very small IPv4 subnets (e.g. /31 with 2 IPv4 addresses) which are usually used for transfer networks. In setups using private IPv4 address ranges this is no big issue. In this case though, official IPv4 addresses were used and in conjunction with the excessive need for VLAN interfaces this limitation caused a lot of wasted official IPv4 addresses.
The access control list (ACL) feature is very limited and rather rudimentary in Dell PowerConnect switches. There is no support for port ranges, no statefulness and each access list has a hard limit of 256 access list entries. All three – and possibly even more – limitations in combination make the ACL feature of Dell PowerConnect switches almost useless. Especially if there are seperate layer 3 networks on the system which are in need of fine-grained traffic control.
From the performance aspect of ACLs i have gotten the impression, that especially IPv6 ACLs are handled by the switches CPU. If IPv6 is used in conjunction with extensive ACLs, this would dramatically impact the network performance of IPv6-based traffic. Admittedly i have no hard proof to support this suspicion.
The out-of-band (OOB) management interface of the Dell PowerConnect switches does not provide a true out-of-band management. Instead it is integrated into the switch as just as another IP interface – although one with a special purpose. Due to this interaction of the OOB with the IP stack of the Dell PowerConnect switch there are side-effects when the switch is running at least one layer 3 instance. In this case, the standard IP routing table of the switch is not only used for routing decisions of the payload traffic, but instead it is also used to determine the destination of packets originating from the OOB interface. This behaviour can cause an asymmetric traffic flow when the systems connecting to the OOB are covered by an entry in the switches IP routing table. Far from ideal when it comes to true OOB management, not to mention the issuses arising when there are also stateful firewall rules involved.
I addressed this limitation with a support case at Dell and got the following statement back:
FASTPATH can learn a default gateway for the service port, the network port,
or a routing interface. The IP stack can only have a single default gateway.
(The stack may accept multiple default routes, but if we let that happen we may
end up with load balancing across the network and service port or some other
combination we don't want.) RTO may report an ECMP default route. We only give
the IP stack a single next hop in this case, since it's not likely we need to
additional capacity provided by load sharing for packets originating on the
box.
The precedence of default gateways is as follows:
- via routing interface
- via service port
- via network port
As per the above precedence, ip stack is having the default gateway which is
configured through RTO. When the customer is trying to ping the OOB from
different subnet , route table donesn't have the exact route so,it prefers the
default route and it is having the RTO default gateway as next hop ip. Due to
this, it egresses from the data port.
If we don't have the default route which is configured through RTO then IP
stack is having the OOB default gateway as next hop ip. So, it egresses from
the OOB IP only.In my opinion this just confirms how the OOB management of the Dell PowerConnect switches is severely broken by design.
Another issue with the out-of-band (OOB) management interface of the Dell PowerConnect switches is that they support only a very limited access control list (ACL) in order to protect the access to the switch. The management ACL only supports one IPv4 ACL entry. IPv6 support within the management ACL protecting the OOB interface is missing altogether.
The Dell PowerConnect have no support for Shortest Path Bridging (SPB) as defined in the IEEE 802.1aq standard. On layer 2 the traditional spanning-tree protocols STP (IEEE 802.1D), RSTP (IEEE 802.1w) or MSTP (IEEE 802.1s) have to be used. This is particularly a drawback in the SAN network shown in the schematic above, due to the protocol determined inactivity of one inter-switch link. With the use of SPB, all inter-switch links could be equally utilizied and a traffic interruption upon link failure and spanning-tree (re)convergence could be avoided.
Another SAN-specific limitation is the incomplete implementation of Data Center Bridging (DCB) in the Dell PowerConnect switches. Although the protocols Priority-based Flow Control (PFC) according to IEEE 802.1Qbb and Congestion Notification (CN) according to IEEE 802.1Qau are supportet, the third needed protocol Enhanced Transmission Selection (ETS) according to IEEE 802.1Qaz is missing in Dell PowerConnect switches. The Dell EqualLogic PS Series storage systems used in the setup shown above explicitly need ETS if DCB should be used on layer 2. Since ETS is not implemented in Dell PowerConnect switches, the traditional layer 2 protocols had to be used in the SAN.
Issues
Not per se an issue, but the baseline CPU utilization on Dell PowerConnect M8024-k switches running layer 3 instances is significantly higher compared to those running only as layer 2 devices. The following CPU utilization graphs show a direct comparison of a layer 3 (upper graph) and a layer 2 (lower graph) device:
The CPU utilization is between 10 and 15% higher once the tasks of processing layer 3 traffic are involved. What kind of switch function or what type of traffic is causing this additional CPU utilization is completely intransparent. Documentation on such in-depth subjects or details on how the processing within the Dell PowerConnect switches works is very scarce. It would be very interesting to know what kind of traffic is sent to the switches CPU for processing instead of being handled by the hardware.
The very high CPU utilization plateau on the right hand side of the upper graph (approximately between 10:50 - 11:05) was due to a bug in processing of IPv6 traffic on Dell PowerConnect switches. This issue caused IPv6 packets to be sent to the switchs CPU for processing instead of doing the forwarding decision in the hardware. I narrowed down the issue by transferring a large file between two hosts via the SCP protocol. In the first case and determined by preferred name resolution via DNS a IPv6 connection was used:
user@host1:~$ scp testfile.dmp user@host2:/var/tmp/ testfile.dmp 8% 301MB 746.0KB/s 1:16:05 ETA
The CPU utilization on the switch stack during the transfer was monitored on the switches CLI:
stack1(config)# show process cpu Memory Utilization Report status bytes ------ ---------- free 170642152 alloc 298144904 CPU Utilization: PID Name 5 Secs 60 Secs 300 Secs ----------------------------------------------------------------- 41be030 tNet0 27.05% 30.44% 21.13% 41cbae0 tXbdService 2.60% 0.40% 0.09% 43d38d0 ipnetd 0.40% 0.11% 0.11% 43ee580 tIomEvtMon 0.40% 0.09% 0.22% 43f7d98 osapiTimer 2.00% 3.56% 3.13% 4608b68 bcmL2X.0 0.00% 0.08% 1.16% 462f3a8 bcmCNTR.0 1.00% 0.87% 1.04% 4682d40 bcmTX 4.20% 5.12% 3.83% 4d403a0 bcmRX 9.21% 12.64% 10.35% 4d60558 bcmNHOP 0.80% 0.21% 0.11% 4d72e10 bcmATP-TX 0.80% 0.24% 0.32% 4d7c310 bcmATP-RX 0.20% 0.12% 0.14% 53321e0 MAC Send Task 0.20% 0.19% 0.40% 533b6e0 MAC Age Task 0.00% 0.05% 0.09% 5d59520 bcmLINK.0 5.41% 2.75% 2.15% 84add18 tL7Timer0 0.00% 0.22% 0.23% 84ca140 osapiWdTask 0.00% 0.05% 0.05% 84d3640 osapiMonTask 0.00% 0.00% 0.01% 84d8b40 serialInput 0.00% 0.00% 0.01% 95e8a70 servPortMonTask 0.40% 0.09% 0.12% 975a370 portMonTask 0.00% 0.06% 0.09% 9783040 simPts_task 0.80% 0.73% 1.40% 9b70100 dtlTask 5.81% 7.52% 5.62% 9dc3da8 emWeb 0.40% 0.12% 0.09% a1c9400 hapiRxTask 4.00% 8.84% 6.46% a65ba38 hapiL3AsyncTask 1.60% 0.45% 0.37% abcd0c0 DHCP snoop 0.00% 0.00% 0.20% ac689d0 Dynamic ARP Inspect 0.40% 0.10% 0.05% ac7a6c0 SNMPTask 0.40% 0.19% 0.95% b8fa268 dot1s_timer_task 1.00% 0.78% 2.74% b9134c8 dot1s_task 0.20% 0.07% 0.04% bdb63e8 dot1xTimerTask 0.00% 0.03% 0.02% c520db8 radius_task 0.00% 0.02% 0.05% c52a0b0 radius_rx_task 0.00% 0.03% 0.03% c58a2e0 tacacs_rx_task 0.20% 0.06% 0.15% c59ce70 unitMgrTask 0.40% 0.10% 0.20% c5c7410 umWorkerTask 1.80% 0.27% 0.13% c77ef60 snoopTask 0.60% 0.25% 0.16% c8025a0 dot3ad_timer_task 1.00% 0.24% 0.61% ca2ab58 dot3ad_core_lac_tas 0.00% 0.02% 0.00% d1860b0 dhcpsPingTask 0.20% 0.13% 0.39% d18faa0 SNTP 0.00% 0.02% 0.01% d4dc3b0 sFlowTask 0.00% 0.00% 0.03% d6a4448 spmTask 0.00% 0.13% 0.14% d6b79c8 fftpTask 0.40% 0.06% 0.01% d6dcdf0 tCkptSvc 0.00% 0.00% 0.01% d7babe8 ipMapForwardingTask 0.40% 0.18% 0.29% dba91b8 tArpCallback 0.00% 0.04% 0.04% defb340 ARP Timer 2.60% 0.92% 1.29% e1332f0 tRtrDiscProcessingT 0.00% 0.00% 0.11% 12cabe30 ip6MapLocalDataTask 0.00% 0.03% 0.01% 12cb5290 ip6MapExceptionData 11.42% 12.95% 9.41% 12e1a0d8 lldpTask 0.60% 0.17% 0.30% 12f8cd10 dnsTask 0.00% 0.00% 0.01% 140b4e18 dnsRxTask 0.00% 0.03% 0.03% 14176898 DHCPv4 Client Task 0.00% 0.01% 0.02% 1418a3f8 isdpTask 0.00% 0.00% 0.10% 14416738 RMONTask 0.00% 0.20% 0.42% 144287f8 boxs Req 0.20% 0.09% 0.21% 15c90a18 sshd 0.40% 0.07% 0.07% 15cde0e0 sshd[0] 0.20% 0.05% 0.02% ----------------------------------------------------------------- Total CPU Utilization 89.77% 92.50% 77.29%
In second case a IPv4 connection was deliberately choosen:
user@host1:~$ scp testfile.dmp user@10.0.0.1:/var/tmp/ testfile.dmp 100% 3627MB 31.8MB/s 01:54
Not only was the transfer rate of the SCP copy process significantly higher – and the transfer time subsequently much lower – in the second case using a IPv4 connection. But the CPU utilization on the switch stack during the transfer using a IPv4 connection was also much lower:
stack1(config)# show process cpu Memory Utilization Report status bytes ------ ---------- free 170642384 alloc 298144672 CPU Utilization: PID Name 5 Secs 60 Secs 300 Secs ----------------------------------------------------------------- 41be030 tNet0 0.80% 23.49% 21.10% 41cbae0 tXbdService 0.00% 0.17% 0.08% 43d38d0 ipnetd 0.20% 0.14% 0.12% 43ee580 tIomEvtMon 0.60% 0.26% 0.24% 43f7d98 osapiTimer 2.20% 3.10% 3.08% 4608b68 bcmL2X.0 4.20% 1.10% 1.22% 462f3a8 bcmCNTR.0 0.80% 0.80% 0.99% 4682d40 bcmTX 0.20% 3.35% 3.59% 4d403a0 bcmRX 4.80% 9.90% 10.06% 4d60558 bcmNHOP 0.00% 0.11% 0.10% 4d72e10 bcmATP-TX 1.00% 0.30% 0.32% 4d7c310 bcmATP-RX 0.00% 0.14% 0.15% 53321e0 MAC Send Task 0.80% 0.39% 0.42% 533b6e0 MAC Age Task 0.00% 0.12% 0.10% 5d59520 bcmLINK.0 1.80% 2.38% 2.14% 84add18 tL7Timer0 0.00% 0.11% 0.20% 84ca140 osapiWdTask 0.00% 0.05% 0.05% 84d3640 osapiMonTask 0.00% 0.00% 0.01% 84d8b40 serialInput 0.00% 0.00% 0.01% 95e8a70 servPortMonTask 0.20% 0.09% 0.11% 975a370 portMonTask 0.00% 0.06% 0.09% 9783040 simPts_task 3.20% 1.54% 1.49% 9b70100 dtlTask 0.20% 5.47% 5.45% 9dc3da8 emWeb 0.40% 0.13% 0.09% a1c9400 hapiRxTask 0.20% 6.46% 6.30% a65ba38 hapiL3AsyncTask 0.40% 0.37% 0.35% abcd0c0 DHCP snoop 0.00% 0.02% 0.18% ac689d0 Dynamic ARP Inspect 0.40% 0.15% 0.07% ac7a6c0 SNMPTask 0.00% 1.32% 1.12% b8fa268 dot1s_timer_task 7.21% 2.99% 2.97% b9134c8 dot1s_task 0.00% 0.03% 0.03% bdb63e8 dot1xTimerTask 0.00% 0.01% 0.02% c520db8 radius_task 0.00% 0.01% 0.04% c52a0b0 radius_rx_task 0.00% 0.03% 0.03% c58a2e0 tacacs_rx_task 0.20% 0.21% 0.17% c59ce70 unitMgrTask 0.60% 0.20% 0.21% c5c7410 umWorkerTask 0.20% 0.17% 0.12% c77ef60 snoopTask 0.20% 0.18% 0.15% c8025a0 dot3ad_timer_task 2.20% 0.80% 0.68% d1860b0 dhcpsPingTask 1.80% 0.58% 0.45% d18faa0 SNTP 0.00% 0.00% 0.01% d4dc3b0 sFlowTask 0.20% 0.03% 0.03% d6a4448 spmTask 0.20% 0.15% 0.14% d6b79c8 fftpTask 0.00% 0.02% 0.01% d6dcdf0 tCkptSvc 0.00% 0.00% 0.01% d7babe8 ipMapForwardingTask 0.20% 0.19% 0.28% dba91b8 tArpCallback 0.00% 0.06% 0.05% defb340 ARP Timer 4.60% 1.54% 1.36% e1332f0 tRtrDiscProcessingT 0.40% 0.14% 0.12% 12cabe30 ip6MapLocalDataTask 0.00% 0.01% 0.01% 12cb5290 ip6MapExceptionData 0.00% 8.60% 8.91% 12cbe790 ip6MapNbrDiscTask 0.00% 0.02% 0.00% 12e1a0d8 lldpTask 0.80% 0.24% 0.29% 12f8cd10 dnsTask 0.00% 0.00% 0.01% 140b4e18 dnsRxTask 0.40% 0.07% 0.04% 14176898 DHCPv4 Client Task 0.00% 0.00% 0.02% 1418a3f8 isdpTask 0.00% 0.00% 0.09% 14416738 RMONTask 1.00% 0.44% 0.44% 144287f8 boxs Req 0.40% 0.16% 0.21% 15c90a18 sshd 0.20% 0.06% 0.06% 15cde0e0 sshd[0] 0.00% 0.03% 0.02% ----------------------------------------------------------------- Total CPU Utilization 43.28% 78.79% 76.50%
Comparing the two above output samples by per process CPU utilization showed that the major share of the higher CPU utilization in the case of a IPv6 connection is allotted to the processes
tNet0,bcmTX,bcmRX,bcmLINK.0,dtlTask,hapiRxTaskandip6MapExceptionData. In a process by process comparison, those seven processes used 60.3% more CPU time in case of a IPv6 connection compared to the case using a IPv4 connection. Unfortunately the documentation on what the individual processes are exactly doing is very sparse or not available at all. In order to further analyze this issue a support case with the collected information was opened with Dell. A fix for the described issue was made availible with firmware version 5.1.9.3The LAN stack of several Dell PowerConnect M8024-k switches showed sometimes erratic behaviour. There were several occasions, where the switch stack would suddenly show a hugely increased latency in packet processing or where it would just stop passing certain types of traffic altogether. Usually a reload of the stack would restore its operation and the increased latency or the packet drops would disappear with the reload as suddenly as they had appeared. The root cause of this was unfortunately never really found. Maybe it was the combination of functions (layer 3, dual stack IPv4 and IPv6, extensive ACLs, etc.) that were running simultaneously on the stack in this setup.
During both planned and unplanned failovers of the master switch in the stack, there is a time period of up to 120 seconds where no packets are processed by the switch stack. This occurs even with continuous forwarding enabled. I've had a strong suspicion that this issue was related to the layer 3 instances running on the switch stack. A comparison between a pure layer 2 stack and a layer 3 enabled stack in a controlled test environment confirmed this. As soon as at least one layer 3 instance was added, the described delay occured on switch failovers. The fact that migrating layer 3 instances from the former master switch to the new one takes some time makes sense to me. What's unclear to me is why this seems to also affect the layer 2 traffic going over the stack.
There were several occasions where the hardware- and software MAC table of the Dell PowerConnect switches got out of sync. While the root cause (hardware defect, bit flip, power surge, cosmic radiation, etc.) of this issue is unknown, the effect was a sudden reboot of affected switch. Luckily we had console servers in place, which were storing a console output history from the time the issue occured. After raising a support case with Dell with the information from the console output, we got a firmware update (v5.1.9.4) in which the issue would not trigger a sudden reboot anymore, but instead log an appropriate message to the switches log. With this fix the out of sync MAC tables will still require a reboot of the affected switch, but this can now be done in a controlled fashion. Still, a solution requiring no reboot at all would have been much more preferrable.
While querying the Dell PowerConnect switches with the SNMP protocol for monitoring purposes, obscure and confusing messages containing the string
MGMT_ACALwould reproducibly be logged into the switches log. See the article Check_MK Monitoring - Dell PowerConnect Switches - Global Status in this blog for the gory details.With a stack of Dell PowerConnect M8024-k switches the information provided via the SNMP protocol would occasionally get out of sync with the information available from the CLI. E.g. the temperature values from the stack
stack1of LAN switches compared to the standalone SAN switchesstandalone{1,2,3,4,5,6}:user@host:# for HST in stack1 standalone1 standalone2 standalone3 stack2 standalone4 standalone5 standalone6; do echo "$HST: "; for OID in 4 5; do echo -n " "; snmpbulkwalk -v2c -c [...] -m '' -M '' -Cc -OQ -OU -On -Ot $HST .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.${OID}; done; done stack1: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4 = No Such Object available on this agent at this OID .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5 = No Such Object available on this agent at this OID standalone1: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 0 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 40 standalone2: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 0 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 37 standalone3: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 0 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 32 stack2: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.2.0 = 0 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 42 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.2.0 = 41 standalone4: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 39 standalone5: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 39 standalone6: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 35
At the same time the CLI management interface of the switch stack showed the correct temperature values:
stack1# show system System Description: Dell Ethernet Switch System Up Time: 89 days, 01h:50m:11s System Name: stack1 Burned In MAC Address: F8B1.566E.4AFB System Object ID: 1.3.6.1.4.1.674.10895.3041 System Model ID: PCM8024-k Machine Type: PowerConnect M8024-k Temperature Sensors: Unit Description Temperature Status (Celsius) ---- ----------- ----------- ------ 1 System 39 Good 2 System 39 Good [...]
Only after a reboot of the switch stack, the information provided via the SNMP protocol:
user@host:# for HST in stack1 standalone1 standalone2 standalone3 stack2 standalone4 standalone5 standalone6; do echo "$HST: "; for OID in 4 5; do echo -n " "; snmpbulkwalk -v2c -c [...] -m '' -M '' -Cc -OQ -OU -On -Ot $HST .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.${OID}; done; done stack1: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.2.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 37 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.2.0 = 37 standalone1: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 0 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 39 standalone2: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 37 standalone3: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 32 stack2: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 0 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.2.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 41 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.2.0 = 41 standalone4: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 38 standalone5: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 38 standalone6: .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.4.1.0 = 1 .1.3.6.1.4.1.674.10895.5000.2.6132.1.1.43.1.8.1.5.1.0 = 34
would again be in sync with the information available from the CLI:
stack1# show system System Description: Dell Ethernet Switch System Up Time: 0 days, 00h:05m:32s System Name: stack1 Burned In MAC Address: F8B1.566E.4AFB System Object ID: 1.3.6.1.4.1.674.10895.3041 System Model ID: PCM8024-k Machine Type: PowerConnect M8024-k Temperature Sensors: Unit Description Temperature Status (Celsius) ---- ----------- ----------- ------ 1 System 37 Good 2 System 37 Good [...]
Conclusion
Although the setup build with the Dell PowerConnect switches and the other hardware components was working and providing its basic, intended functionality, there were some pretty big and annoying limitations associated with it. A lot of these limitations would have not been that significant to the entire setup if certain design descisions would have been made more carefully. For example if the layer 3 part of the LAN would have been implemented in external network components or if a proper fully meshed, fabric-based SAN would have been favored over what can only be described as a legacy technology. From the reliability, availability and serviceability (RAS) points of view, the setup is also far from ideal. By daisy-chaining the Dell PowerEdge M1000e blade chassis, stacking the LAN switches, stretching the LAN and SAN over both chassis and by connecting external devices through the external ports of the Dell PowerConnect switches, there are a lot of parts in the setup that are depending on each other. This makes normal operations difficult at best and can have disastrous effects in case of a failure.
In retrospect, either using pure pass-through network modules in the Dell PowerEdge M1000e blade chassis in conjunction with capcable 10GE top-of-rack switches or using the much more capable Dell Force10 MXL switches in the Dell PowerEdge M1000e blade chassis seem to be better solutions. The uptick for Dell Force10 MXL switches of about €2000 list price per device compared to the Dell PowerConnect switches seems negligible compared to the costs that arose through debugging, bugfixing and finding workarounds for the various limitations of the Dell PowerConnect switches. In either case a pair of capable, central layer 3 devices for gateway redundancy, routing and possibly fine-grained traffic control would be advisable.
For simpler setups, without some of the more special requirements of this particular setup, the Dell PowerConnect switches still offer a nice price-performance ratio. Especially with regard to their 10GE port density.
2015-08-15 // Dell EqualLogic PS Series - Security
An initial setup is always a good opportunity to take a more in-depth look at systems, while they are not yet in production. In this case i'm looking at one of the advertised security measures of Dell EqualLogic PS Series systems.
We're currently in the process of implementing iSCSI-based Dell EqualLogic PS Series systems. Specifically we're using PS-M4110E and PS-M4110X models in several Dell M1000e blade chassis. The EqualLogic storages and the hosts they provide storage space for are being connected with PowerConnect M8024-K switches. The switches are located in the slots B1 and B2 of the blade chassis and are dedicated for iSCSI traffic with 10 gigabit ethernet.
Although the separation of SAN and LAN could be considered enough security, i was really pleased to read in the Dell EqualLogic Group Manager Administrator's Manual - PS Series Firmware Version 7.0 (110-6152-EN-R1) that the folks at EqualLogic thought otherwise and added further security measures in order to protect the EqualLogic PS Series systems from unauthorized access to its management functions over the iSCSI network. A quote from page 76 of said document reads:
[…]
About Dedicated Management Networks
For increased security, or if your environment requires the separation of management traffic and iSCSI traffic, you can configure a dedicated management network (DMN) that is used only for administrative access to the group. The management network is separate from the network that handles iSCSI traffic to the group.
- Without a dedicated management network (the default configuration), administrators connect to the group IP address for both administrative access to the group and iSCSI initiator access to iSCSI targets (volumes and snapshots).
- With a dedicated management network, administrators do not use the group IP address for administrative access to the group. Instead, administrators connect to the management network address. All iSCSI traffic, including traffic by replication partners, and access to Dell EqualLogic Auto-Snapshot Manager/Linux Edition (ASM/LE), Dell EqualLogic Auto-Snapshot Manager/Microsoft Edition (ASM/ME), and Dell EqualLogic Virtual Storage Manager for VMware (formerly ASM/VE), continues to use the group IP address. SAN Headquarters can connect to the group using either the management network address or the iSCSI address.
[…]
And further on page 78 of the same document:
[…]
When you complete the management network configuration, administrators cannot log in to the group using the group IP address. Instead, administrators must use the new management IP address. Any open GUI or CLI sessions using the group IP address eventually time out and close.
After configuring a dedicated management network, you might need to:
- Inform administrators of the new management network IP address.
- If you run the Group manager GUI as a standalone application and have a shortcut on the computer's desktop, the group address in the shortcut is not updated with the new management address. You must uninstall and then reinstall the GUI application.
- If you are running SAN Headquarters, you must update the group IP address in the application to the dedicated management address. For more information, see the SAN Headquarters documentation.
[…]
Judging from those two sections it would appear that the EqualLogic PS Series systems have no or at least a very small attack surface on the – potentially untrustworthy – host-facing network dedicated to iSCSI traffic. In open systems this is usually achieved by binding the services which are necessary for the management function to a specific network interface, instead of letting them listen on all available interfaces.
Using a DMN and thus separating the management traffic from the iSCSI traffic resulted in our case in the following configuration example:
group1-grp(member_group1)> eth show Name ifType ifSpeed Mtu Ipaddress Status Errors DCB ---- --------------- ---------- ---- ----------------------------- ------ ------ ------ eth0 ethernet-csmacd 10 Gbps 9000 10.0.0.1 up 0 off eth1 ethernet-csmacd 100 Mbps 1500 123.123.123.123 up 0 off
group1-grp(member_group1)> eth select 0 show _______________________________ Eth Information _______________________________ Name: eth0 Status: up Changed: Mon Jul 20 12:23:15 2015 Type: ethernet-csmacd DesiredStatus: up Mtu: 9000 Speed: 10 Gbps HardwareAddress: B0:83:FE:CC:52:C1 IPAddress: 10.0.0.1 NetMask: 255.255.0.0 IPv6Address: Description: group1 iSCSI Interface SupportsManagement: no ManagementStatus: normal DCB: off
group1-grp(member_group1)> eth select 1 show _______________________________ Eth Information _______________________________ Name: eth1 Status: up Changed: Wed Jul 29 08:33:35 2015 Type: ethernet-csmacd DesiredStatus: up Mtu: 1500 Speed: 100 Mbps HardwareAddress: B0:83:FE:CC:52:C2 IPAddress: 123.123.123.123 NetMask: 255.255.255.0 IPv6Address: Description: group1 Management Interface SupportsManagement: only ManagementStatus: mgmt DCB: off
Here the lines with the SupportsManagement options could be construed in the way, that management access is not possible over the eth0 interface, which in this configuration is the connection to the host-facing iSCSI network.
From previous lessons learned not to be overly trusty of lofty vendor promises, i decided to double check this with the simple use of the nmap network and port scanner. The results of the TCP and UDP port scans against both the member and the group IP address are shown below.
Member IP - TCP scan:
root@host:~$ nmap -sS -p 0-65535 10.0.0.1 Starting Nmap 6.00 ( http://nmap.org ) at 2015-07-15 11:14 CEST Nmap scan report for ******** (10.0.0.1) Host is up (0.000097s latency). Not shown: 9991 closed ports PORT STATE SERVICE 21/tcp open ftp 22/tcp open ssh 80/tcp open http 443/tcp open https 2606/tcp open netmon 3002/tcp open exlm-agent 3003/tcp open cgms 3260/tcp open iscsi 9876/tcp open sd 20002/tcp open commtact-http 20003/tcp open unknown 25555/tcp open unknown MAC Address: B0:83:FE:CC:52:C1 (Unknown) Nmap done: 1 IP address (1 host up) scanned in 107.66 seconds
Member IP - UDP scan:
root@host:~$ nmap -sU -p 0-65535 10.0.0.1 Starting Nmap 6.00 ( http://nmap.org ) at 2015-07-20 09:27 CEST Nmap scan report for ******** (10.0.0.1) Host is up (0.000086s latency). Not shown: 65532 closed ports PORT STATE SERVICE 0/udp open|filtered unknown 123/udp open ntp 161/udp open snmp 65519/udp open|filtered unknown MAC Address: B0:83:FE:CC:52:C1 (Unknown) Nmap done: 1 IP address (1 host up) scanned in 2.55 seconds
Group IP - TCP scan:
root@host:~$ nmap -sS -p 0-65535 10.0.0.2 Starting Nmap 6.00 ( http://nmap.org ) at 2015-07-15 11:17 CEST Nmap scan report for ******** (10.0.0.2) Host is up (0.00010s latency). Not shown: 9991 closed ports PORT STATE SERVICE 21/tcp open ftp 22/tcp open ssh 80/tcp open http 443/tcp open https 2606/tcp open netmon 3002/tcp open exlm-agent 3003/tcp open cgms 3260/tcp open iscsi 9876/tcp open sd 20002/tcp open commtact-http 20003/tcp open unknown 25555/tcp open unknown MAC Address: B0:83:FE:CC:52:C1 (Unknown) Nmap done: 1 IP address (1 host up) scanned in 103.71 seconds
Group IP - UDP scan:
root@host:~$ nmap -sU -p 0-65535 10.0.0.2 Starting Nmap 6.00 ( http://nmap.org ) at 2015-07-20 09:28 CEST Nmap scan report for ******** (10.0.0.2) Host is up (0.00013s latency). Not shown: 65532 closed ports PORT STATE SERVICE 0/udp open|filtered unknown 123/udp open ntp 161/udp open snmp 65519/udp open|filtered unknown MAC Address: B0:83:FE:CC:52:C1 (Unknown) Nmap done: 1 IP address (1 host up) scanned in 3.07 seconds
These scan results are pretty disappointing with regard to the expected additional security measures mentioned above.
An actual login test via SSH and FTP was successful and i guess a login via Telnet would have been successful too, if the protocol hadn't already been disabled in our configuration. This means there is also no filter on the application layer preventing access to the management functions, which wouldn't have been recognized by the simple port scan above.
As described earlier it shouldn't be too hard binding the services which are necessary for the management function to a specific network interface. I can't help but wonder why EqualLogic didn't follow through with this, especially since it's already described in the product manual. Maybe there were too many feature requests from the customer side or even technical requirements to better integrate the EqualLogic PS Series systems with certain host systems. Even then i wonder why EqualLogic didn't at least provide some means of selectively enabling or disabling the access to the management function from the iSCSI network with some kind of configuration parameter. In any case, the situation at hand – describing one thing and implementing another – seems to be the least favorable one to me.
