Posts Tagged ‘STP’

Automating VLAN Configuration on Dell FTOS Switches via GVRP

Saturday, February 22nd, 2014

GARP VLAN Registration Protocol (GVRP) is a standards-based protocol defined in the IEEE 802.1Q specification that provides for automatic VLAN configuration on switches. The Generic Attribute Registration Protocol (GARP) is used by switches supporting GVRP to register/de-register attribute values such as VLAN IDs between switches within the network. GVRP is the standards-based equivalent to Cisco’s Virtual Trunk Protocol (VTP). To read more about Cisco VTP, read my prior blog at For this blog, I utilize 2 x Dell S60s [FTOS ]and 1x Dell S50N [FTOS]. Below is the network diagram for this lab. (more…)


Distributed Core Network Architecture

Friday, January 18th, 2013

There is no doubt you have probably heard by now the importance of supporting ‘east-west’ traffic flow in large data center networks. So why is this and what does it mean? And when Gartner claims that 80 percent of data center network traffic now travels from server-to-server, just what impact does this have on network design/architecture? (more…)


Dell Force10 – Layer 2 Multipathing via Virtual Link Trunking (VLT)

Tuesday, December 18th, 2012

In this blog I use one Dell Force10 S50N [FTOS] and three Dell Force10 S4810 switches [FTOS] to demonstrate Dell Force10′s layer 2 mulipathing technology called Virtual Link Trunking (VLT). With VLT, you can create a LAG for a server, switch, or any device that supports LACP to two different upstream switches.

Traditionally, a LAG from an access switch or server could only connect to a single upstream switch. For redundanacy purposes, many users would implement stacking on the upstream switches and then use a port-channel/LAG up to the stacked switch now seen as one logical entity. However, stacking is not the preferred solution here. Two main reasons for this is that stacking provides a single control plane mechanism that is managed by the master switch; there is no hitless failover. Compare this to VLT which provides a dual control plane mechanism and is hitless in nature. Additionally, when upgrading the switch firmware, the entire stack would need to be brought down. With VLT, one switch can be upgraded at a time without bringing down the other switch.

Stacking is more seen at the ToR or access layer. The ToR switches are usually stacked and VLT is then used upstream to the aggregate and core switches. However, if the ToR switch supports VLT such as the S4810 does, VLT can also be used from the switch down to the server. 1 GbE switches like the Dell S50N and Dell S60 do not support VLT, so, in these cases, stacking can still be employed.

In the least recommended approach, if no VLT or stacking is used at the aggregate layer connecting to the ToR on a layer 2 network, spanning tree protocol (STP) would need to be employed to block redundant links. This would create link and switch level redundancy. The issue with this is that you lose half the ports/bandwidth on the switch. By leveraging VLT, you can have an active-active multi-path connection from an access server/switch to two upstream switches seen as one logical entity employing a dual control plane mechanism. No putting-up with STP or blocked ports! (more…)


Networking: Spanning Tree Protocol Basics [Video]

Sunday, April 15th, 2012

This video covers some of the basics of how Spanning Tree Protocol (STP) works in a network. To learn more about Spanning Tree Protocol see some of my prior blogs on STP. (more…)


Configuring PVST+ on Cisco Switches

Wednesday, February 1st, 2012

Per VLAN Spanning Tree Plus (PVST+) is a flavor of Spanning Tree Protocol (see prior blog, Default STP Behavior on Cisco Switches) which maintains a spanning tree instance for each VLAN in the network. This means certain VLAN trunks (using 802.1q) can be forwarded for some VLANs while being blocked for others. Further, changes in one STP domain will not effect other spanning tree instances on other VLANs. Additionally, since each VLAN is treated as a separate network, layer 2 load balancing can be accomplished by forwarding some VLANs on one trunk and other VLANs on another trunk. (more…)


Default STP Behavior on Cisco Switches

Tuesday, January 31st, 2012

In a prior blog, Functionality of Layer 2 Switches/Bridges, I discussed the core functionality of layer 2 switches. In this blog, I hit upon the Spanning Tree Protocol (STP) used on layer 2 switches to prevent loops. As mentioned before, loops can be created via layer 2 switches by using more than one link to connect to the same switches. This is often done for redundancy purposes but is not possible without STP. (more…)


Functionality of Layer 2 Switches/Bridges

Thursday, May 26th, 2011

Layer 2 Switching

Layer 2 Switching (STP Needed)

Layer 2 switches and bridges switch frames on a network while layer 3 routers route packets between networks. I once heard a network engineer being asked if a network can be made faster if the network is optimized to use more switches than routers. The network engineer answered that it shouldn’t matter. Of course, this is wrong. Think about it, if your network is just switching, the switches do not have to concern themselves with looking at the network layer; this significantly cuts down on the overhead since there is no need to decode the network header information at every stop like is done by a router. There are some concerns to keep in mind if your network starts to get too big which I discuss near the end of the blog. (more…)